U.S. patent application number 15/686012 was filed with the patent office on 2018-11-22 for rank indicator adaptation based on downlink error rate.
The applicant listed for this patent is T-Mobile USA, Inc.. Invention is credited to Jeff Ahmet, Ming Shan Kwok.
Application Number | 20180337764 15/686012 |
Document ID | / |
Family ID | 64272223 |
Filed Date | 2018-11-22 |
United States Patent
Application |
20180337764 |
Kind Code |
A1 |
Kwok; Ming Shan ; et
al. |
November 22, 2018 |
Rank Indicator Adaptation Based on Downlink Error Rate
Abstract
A method of inducing increased throughput to a telecommunication
device, in which the telecommunication device sets a rank indicator
(RI) based on a number of multiple-input multiple-output (MIMO)
data streams received and decoded from a base station, determines
an error rate of the decoded MIMO data streams, and increases the
RI when it is less than a maximum RI and the error rate is less
than an RI increase threshold. The RI is reported from the
telecommunication device to the base station, which uses the
increased RI to increase the number of MIMO data streams it sends
to the telecommunication device.
Inventors: |
Kwok; Ming Shan; (Seattle,
WA) ; Ahmet; Jeff; (Issaquah, WA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
T-Mobile USA, Inc. |
Bellevue |
WA |
US |
|
|
Family ID: |
64272223 |
Appl. No.: |
15/686012 |
Filed: |
August 24, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62507006 |
May 16, 2017 |
|
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|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04B 7/0632 20130101;
H04L 1/0003 20130101; H04L 1/1812 20130101; H04W 72/08 20130101;
H04L 5/0057 20130101; H04L 1/0026 20130101; H04B 7/063 20130101;
H04B 7/0486 20130101; H04L 1/0009 20130101; H04W 72/0413 20130101;
H04L 1/203 20130101; H04W 72/0473 20130101; H04W 72/06
20130101 |
International
Class: |
H04L 5/00 20060101
H04L005/00; H04W 72/04 20060101 H04W072/04; H04L 1/18 20060101
H04L001/18; H04W 72/08 20060101 H04W072/08 |
Claims
1. A method of inducing increased throughput to a telecommunication
device, comprising: receiving and decoding, by the
telecommunication device, one or more multiple-input
multiple-output (MIMO) data streams from a base station via a
plurality of receiver antennas of the telecommunication device;
setting, by the telecommunication device, a rank indicator (RI) to
the number of decoded MIMO data streams; determining, by the
telecommunication device, an error rate of the decoded MIMO data
streams; increasing, by the telecommunication device, the RI when
the RI is less than a maximum RI and the error rate is less than an
RI increase threshold, wherein the RI is increased to a value less
than or equal to the maximum RI; and sending, by the
telecommunication device, a report including the RI from the
telecommunication device to the base station, such that the base
station uses the RI to increase the number of MIMO data streams it
sends to the telecommunication device.
2. The method of claim 1, wherein the maximum RI is the lowest
number between the number of receiver antennas at the
telecommunication device and the number of transmitter antennas at
the base station.
3. The method of claim 2, wherein in a 4.times.4 MIMO configuration
the number of receiver antennas at the telecommunication device is
four, the number of transmitter antennas at the base station is
four, and the maximum RI is four.
4. The method of claim 1, wherein the error rate is a downlink
block error rate (DL BLER).
5. The method of claim 1, further comprising: determining a Channel
Quality Indicator (CQI) by the telecommunication device based on
the error rate; and including, by the telecommunication device, the
CQI in the report.
6. The method of claim 5, wherein the CQI is determined by the
telecommunication device by identifying a modulation and coding
scheme (MCS) associated with the CQI that is expected to lead to
the error rate staying below a predefined acceptable error rate
when the MIMO data signals are sent by the base station using the
MCS.
7. The method of claim 1, further comprising: monitoring, by the
telecommunication device, the error rate of subsequent MIMO data
streams received from the base station following sending the
report; and reducing, by the telecommunication device, the RI from
the increased level in a subsequent report sent to the base station
when the error rate goes above a predefined acceptable error
rate.
8. A telecommunication device, comprising: a plurality of receiving
antennas configured to receive multiple-input multiple-output
(MIMO) data streams from a base station; at least one transmitter
antenna; a radio interface configured to decode the MIMO data
streams; and one or more processors configured to: set a rank
indicator (RI) to the number of decoded MIMO data streams;
determine an error rate of the decoded MIMO data streams;
increasing the RI device when the RI is less than a maximum RI and
the error rate is less than an RI increase threshold, wherein the
RI is increased to a value less than or equal to the maximum RI;
and send a report including the RI via the at least one transmitter
antenna to the base station, such that the base station is induced
to use the RI to increase the number of MIMO data streams it sends
to the plurality of receiving antennas.
9. The telecommunication device of claim 8, wherein the maximum RI
is the lowest number between the number of the plurality of
receiver antennas and a number of transmitter antennas at the base
station.
10. The telecommunication device of claim 8, wherein in a 4.times.4
MIMO configuration the number of the plurality of receiver antennas
is four, the number of transmitter antennas at the base station is
four, and the maximum RI is four.
11. The telecommunication device of claim 8, wherein the error rate
is a downlink block error rate (DL BLER).
12. The telecommunication device of claim 8, wherein the one or
more processors are further configured to: determine a Channel
Quality Indicator (CQI) based on the error rate; and include the
CQI in the report.
13. The telecommunication device of claim 12, wherein the CQI is
determined by identifying a modulation and coding scheme (MCS)
associated with the CQI that is expected to lead to the error rate
staying below a predefined acceptable error rate when the MIMO data
streams are sent by the base station using the MCS.
14. The telecommunication device of claim 8, wherein the one or
more processors are further configured to: monitor the error rate
of subsequent MIMO data streams received from the base station
following sending the report; and reduce the RI from the increased
level in a subsequent report sent to the base station when the
error rate goes above a predefined acceptable error rate.
15. One or more non-transitory computer-readable media storing
computer-executable instructions that, when executed by a
telecommunication device, cause the telecommunication device to
perform operations comprising: setting a rank indicator (RI) to a
number of multiple-input multiple-output (MIMO) data streams that
were received from a base station and decoded at the
telecommunication device via a plurality of receiver antennas;
determining an error rate of the decoded MIMO data streams;
increasing the RI when the RI is less than a maximum RI and the
error rate is less than an RI increase threshold, wherein the RI is
increased to a value less than or equal to the maximum RI; and
sending a report including the RI to the base station, such that
the base station is induced to use the RI to increase the number of
MIMO data streams it sends to the telecommunication device.
16. The one or more non-transitory computer-readable media of claim
15, wherein the maximum RI is the lowest number between the number
of receiver antennas at the telecommunication device and the number
of transmitter antennas at the base station.
17. The one or more non-transitory computer-readable media of claim
15, wherein in a 4.times.4 MIMO configuration the number of
receiver antennas at the telecommunication device is four, the
number of transmitter antennas at the base station is four, and the
maximum RI is four.
18. The one or more non-transitory computer-readable media of claim
15, wherein the error rate is a downlink block error rate (DL
BLER).
19. The one or more non-transitory computer-readable media of claim
15, wherein the operations further comprise: determining a Channel
Quality Indicator (CQI) based on the error rate; and including the
CQI in the report.
20. The one or more non-transitory computer-readable media of claim
15, wherein the CQI is determined by identifying a modulation and
coding scheme (MCS) associated with the CQI that is expected to
lead to the error rate staying below a predefined acceptable error
rate when the MIMO data signals are sent by the base station using
the MCS.
Description
RELATED APPLICATIONS
[0001] This U.S. patent application claims priority to provisional
U.S. Patent Application No. 62/507,006, filed May 16, 2017, the
entirety of which is incorporated herein by reference.
BACKGROUND
[0002] Wireless communication devices are commonly used to browse
the Internet, transmit files, stream music and video, and perform
other tasks that involve wirelessly receiving data from a network.
The user experience is improved when such data transmissions occur
quickly, and thus network operators and device manufacturers strive
to improve data throughput.
[0003] One technique for improving data throughput between devices
uses multiple-input multiple-output (MIMO) technology. In a MIMO
configuration, devices can have multiple transmitting antennas
and/or multiple receiving antennas, such that multiple data streams
can be sent between the multiple antennas over the same radio
channel. As each data stream can have substantially the same
capacity for transmitting data, increasing the number of data
streams can accordingly increase the amount of data that can be
transmitted, thereby improving throughput. However, there is a risk
that some of the MIMO data streams may not be properly decoded at
the receiving device due to interference, noise, or other
issues.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] The detailed description is set forth with reference to the
accompanying figures. In the figures, the left-most digit(s) of a
reference number identifies the figure in which the reference
number first appears. The use of the same reference numbers in
different figures indicates similar or identical items or
features.
[0005] FIG. 1 depicts a telecommunication device in wireless
communication with a network base station via multiple data streams
using multiple-input multiple-output (MIMO) techniques.
[0006] FIG. 2 depicts a graph in which a measured error rate can be
compared to a predefined acceptable error rate and/or an RI
increase threshold.
[0007] FIG. 3 depicts an example system architecture for a
telecommunication device.
[0008] FIG. 4 depicts a flow chart of a method for increasing
throughput to a telecommunication device by inducing a base station
to transmit additional data streams using MIMO techniques.
DETAILED DESCRIPTION
Introduction
[0009] In a radio access network (RAN), a network base station can
wirelessly transmit data to a telecommunication device. The data
throughput to the telecommunication device can depend, at least in
part, on a Modulation and Coding Scheme (MCS) used by the base
station, as well as the number of multiple-input multiple-output
(MIMO) data streams sent by the base station to the
telecommunication device.
[0010] An MCS can indicate a particular modulation scheme used by a
base station, such as a quadrature amplitude modulation (QAM)
scheme that increases throughput by combining multiple modulated
signals into a single channel. The amount of the throughput
increase can depend on the particular QAM scheme. For example, an
MCS that uses 256-QAM can lead to a higher throughput that an MCS
that uses 64-QAM, because 256-QAM can carry 8 bits per symbol while
64-QAM can carry 6 bits per symbol.
[0011] MIMO techniques can also be used to increase throughput to
the telecommunication device when the telecommunication device and
base station have multiple transmitting and/or receiving antennas.
For example, the base station can transmit multiple MIMO data
streams using different antennas, and the telecommunication device
can receive the transmitted signals and decode them back into the
original data streams. Each MIMO data stream can have substantially
the same data capacity, and accordingly increasing the number of
MIMO data streams sent by the base station can increase throughput
to the telecommunication device.
[0012] A base station can combine MIMO techniques and modulation
schemes defined by an MCS to adjust the throughput to a
telecommunication device. For example, in some situations peak data
throughput of over 1 Gigabit per second (Gbps) can be achieved when
four data streams can be sent and received in a 4.times.4 MIMO
system using a 256-QAM MCS.
[0013] However, sending the maximum number of data streams using
the best MCS is not always possible. Due to the multipath
propagation of the MIMO data streams, interference, noise, and/or
other issues can make it difficult to decode each of the originally
sent data streams. Accordingly, the telecommunication device can
report information to the base station about the signals it is
receiving, such that the base station can adjust how it is sending
signals to the telecommunication device based on current radio
conditions.
[0014] The report sent by the telecommunication device can include
a Rank Indicator (RI) and a Channel Quality Indicator (CQI). The RI
indicates a MIMO layer associated with a number of MIMO data
streams decoded by the telecommunication device. The CQI indicates
the quality of signals received by the telecommunication device, in
some examples and can be based on an error rate measured by the
telecommunication device, such as a downlink Block Error Rate (DL
BLER). For example, a telecommunication device can determine the DL
BLER of received signals, and report a CQI value to the base
station that is associated with an MCS expected to lead to a DL
BLER under a predefined acceptable BLER, such as a BLER of 10%. In
some examples the telecommunication device's report can include the
measured error rate instead of, or in addition to, the CQI.
[0015] After receiving reported RI and CQI values from the
telecommunication device, the base station can select the number of
MIMO data streams to send based on the reported RI and the MCS to
use based on the reported CQI. For example, if the
telecommunication device reports an RI value of "3" and a
particular CQI value, the base station can follow that information
to transmit three MIMO data streams using an MCS associated with
the reported CQI value.
[0016] However, test results have shown that telecommunications
devices prioritize sending a CQI value linked to a higher MCS over
sending a higher RI value. For example, in tests in which the
maximum RI value was four and an acceptable error rate threshold
was set at a DL BLER of 10%, when telecommunication devices
measured a DL BLER of only 2% or another percentage well below the
10% acceptable BLER threshold, they often reported a high CQI but a
lower than maximum RI value of "3." The difference between the
measured error rates and the acceptable error rate threshold in
these tests indicates that, as will be discussed below, in some
cases the telecommunication device can handle one or more
additional MIMO data streams without the measured error rate going
over the acceptable error rate threshold. Sending additional MIMO
data streams when such capacity exists would lead to increased
throughput to the telecommunication device.
[0017] This disclosure describes various systems and processes that
can be implemented at telecommunication device to adaptively induce
a base station to send one or more additional MIMO data streams in
certain situations, in order to increase the data throughput to the
telecommunication device. As described herein, when the
telecommunication device measures an RI value that is less than a
maximum RI, but it measures an error rate below an acceptable error
rate threshold, it can report an inflated RI value to the base
station that is higher than the measured RI value. The base station
can then follow the reported inflated RI value to send an increased
number of MIMO data streams to the telecommunication device.
Example Environment
[0018] FIG. 1 depicts a telecommunication device 102 in wireless
communication with a network base station 104 via multiple data
streams 106 using multiple-input multiple-output (MIMO) techniques.
As will be described below, the base station 104 can determine the
number of data streams 106 to transmit to the telecommunication
device 102 based on a report 108 sent from the telecommunication
device 102 to the base station 104 about previous transmissions it
has received from the base station 104. The report 108 can include
a Rank Indicator (RI) 110 and/or a Channel Quality Indicator (CQI)
112.
[0019] A telecommunication device 102 can be any device that
wirelessly connects to a base station 104, such as a smart phone, a
cellular phone, a personal digital assistant (PDA), a personal
computer (PC), a laptop, a desktop, a workstation, a media player,
a tablet, an electronic book device, a gaming device, a television,
a media center, a smart watch, or any other type of computing or
communication device. An example telecommunication device 102 is
illustrated in greater detail in FIG. 3 and is described in detail
below with reference to that figure.
[0020] A base station 104 can be a node or other access point that
provides a connected telecommunication device 102 with access to a
telecommunications network through a wireless access technology,
such as Long Term Evolution (LTE)/LTE Advanced technology,
High-Speed Data Packet Access (HSDPA)/Evolved High-Speed Packet
Access (HSPA+) technology, Universal Mobile Telecommunications
System (UMTS) technology, Code Division Multiple Access (CDMA)
technology, Global System for Mobile Communications (GSM)
technology, WiMax.RTM. technology, and/or WiFi.RTM. technology. For
example, in an LTE network a base station 104 can be an eNode
B.
[0021] A telecommunication device 102 and base station 104 can each
have multiple antennas 114 for transmitting and/or receiving data,
such that they can use MIMO techniques to send and/or receive
different data streams 106 with different antennas 114. In general,
the arrangement of transmitter antennas 114 and receiver antennas
114 in a MIMO system can be expressed as N.times.M, with N
indicating the number of transmitter antennas 114 and M indicating
the number of receiver antennas 114. For example, devices in a
2.times.2 MIMO system can have two transmitter antennas 114 and two
receiver antennas 114, while devices in a 4.times.4 MIMO system can
have four transmitter antennas 114 and four receiver antennas 114.
While in some examples N can be equal to M, in other examples N and
M can be different.
[0022] Using MIMO, the base station 104 can split data to be
transmitted to the telecommunication device 102 into multiple data
streams 106 using multiplexing, such as open-loop or closed-loop
spatial multiplexing. The base station 104 can transmit each of the
multiple data streams 106 with a different transmitting antenna 114
over the same radio channel. The signals transmitted from each
transmitting antenna 114 can take different paths to the
telecommunication device 102. Accordingly, parts of some or all of
the different signals from the different transmitting antennas 114
can be received at multiple receiving antennas 114 at the
telecommunication device 102. The telecommunication device 102 can
decode the received signals and reconstruct the original data
streams 106.
[0023] Each data stream 106 can have substantially the same data
capacity. Accordingly, each additional data stream 106 that can be
transmitted from the base station 104 and be received and decoded
by the telecommunication device 102 using MIMO techniques can
correspondingly increase the data throughput to the
telecommunication device 102.
[0024] The base station 104 can also transmit the data streams 106
to the telecommunication device 102 using a Modulation and Coding
Scheme (MCS). An MCS can define a modulation scheme, code rate,
and/or other attributes that the base station 104 can use when
sending data transmissions to the telecommunication device 102,
such as a quadrature amplitude modulation (QAM) scheme that can
increase throughput by combining multiple modulated signals into a
single channel. For example, an MCS can identify a particular
modulation scheme, such as 256-QAM, 64-QAM, 16-QAM, or any other
modulation scheme. The number prefacing "QAM" in these schemes can
indicate the number of bits that can be carried per symbol in that
scheme. For instance, 256-QAM can carry 8 bits per symbol, while
64-QAM can carry 6 bits per symbol.
[0025] As mentioned above, the telecommunication device 102 can
send back a report 108 to the base station 104 about how the data
streams 106 are being received, including RI 110 and/or CQI 112
values. In various examples, the telecommunication device 102 can
send a report 108 periodically at regular intervals, at irregular
intervals or predefined times, upon request by the base station
104, or upon the occurrence of a reporting event.
[0026] The RI 110 in the report 108 can indicate a number of data
streams 106 that the telecommunication device 102 is requesting
from the base station 104. The telecommunication device 102 can
determine the value of the RI 110 based at least in part on the
number of data streams 106 it decoded within signals received from
the base station 104. Selection of the RI 110 value will be
discussed in more detail below.
[0027] The reported RI 110 can be less than or equal to a maximum
RI associated with the MIMO configurations of the telecommunication
device 102 and the base station 104. The maximum RI can be the
maximum number of MIMO data streams 106 that could be transmitted
from the base station 104 to the receiver antennas 114 of the
telecommunication device 102, as limited by the number of
transmitter antennas 114 in the base station 104 and the number of
receiver antennas 114 in the telecommunication device 102. As such,
when the base station 104 has X transmitter antennas 114 and the
telecommunication device 102 has Y receiver antennas 114, the
maximum RI can be at most the lower of X and Y.
[0028] For example, if the telecommunication device 102 has four
receiver antennas 114 and a base station 104 is capable of sending
four data streams 106 to those four receiving antennas 114 in a
4.times.4 MIMO configuration, the maximum RI can be set to four. In
other examples the maximum RI can be set to a higher or lower value
determined by the number of receiver antennas 114 in the
telecommunication device 102 and/or a maximum number of data
streams 106 a base station 104 can send to those receiving antennas
114 using MIMO techniques. For instance, in an 8.times.8 MIMO
configuration, the maximum RI can be set to eight.
[0029] The CQI 112 in the report 108 can be based on an error rate
200 measured by the telecommunication device. FIG. 2 depicts a
graph in which a measured error rate 200 can be compared to a
predefined acceptable error rate 202 and/or an RI increase
threshold 204 as will be discussed further below. In some examples
the telecommunication device 102 can include the measured error
rate 200 in the report 108 in addition to, or in place of, the CQI
112.
[0030] In some examples an error rate 200 can be a downlink Block
Error Rate (DL BLER) determined by the telecommunication device.
The telecommunication device 102 can use an error detection
technique, such as analyzing a cyclic redundancy check (CRC) code
in a received data block, to determine when a received data block
contains an error. The DL BLER can be the percentage of the total
number of data blocks that are found to have an error. The
telecommunication device 102 can thus determine the DL BLER of
received signals, and include a CQI 112 in the report 108 that is
associated with an MCS expected to lead to a DL BLER under a
predefined acceptable error rate 202, such as a DL BLER of 10%. In
other examples the error rate 200 can be measured as a bit error
rate (BER), signal to noise ratio (SNR), or any other measure of
errors within received data.
[0031] When the base station 104 receives a report 108 including an
RI 110 and a CQI 112 values from the telecommunication device 102,
it can use those reported values to adjust or select the number of
data streams 106 to send to the telecommunication device 102 using
MIMO, and/or the MCS to use when sending those data streams 106.
For example, when the reported RI 110 is "3" and the reported CQI
112 is associated with an MCS, the base station 104 can send the
telecommunication device 102 three MIMO data streams 106 using that
MCS. While the base station 104 may choose to adjust the MCS, it
does not attempt to override the reported RI 110.
[0032] As will be discussed below, in some situations the
telecommunication device 102 can change the data in the report 108
from what it would otherwise include, in order to adaptively induce
the base station 104 to increase the number of data streams 106 it
sends to the telecommunication device 102 using MIMO. By inducing
the base station 104 to transmit an increased number of data
streams 106 in these situations, data throughput to the
telecommunication device 102 can be increased.
Example Architecture
[0033] FIG. 3 depicts an example system architecture for a
telecommunication device 102, in accordance with various examples.
As shown, in addition to the antennas 114 discussed above, a
telecommunication device 102 can also include a memory 302 that
stores modules and data 304, processor(s) 306, radio interfaces
308, a display 310, output devices 312, input devices 314, and/or a
drive unit 316 including a machine readable medium 318.
[0034] In various examples, memory 302 generally includes both
volatile memory and non-volatile memory, such as RAM, ROM, EEPROM,
Flash Memory, a hard drive, a memory card, optical storage,
magnetic cassettes, magnetic tape, magnetic disk storage or other
magnetic storage devices, or any other medium. In some examples
memory 302 can also include a SIM (subscriber identity module)
card, which is a removable memory card used to identify a user of
the telecommunication device 102 to a telecommunication network.
Memory 302 can also be described as computer storage media and may
include volatile and nonvolatile, removable and non-removable media
implemented in any method or technology for storage of information,
such as computer readable instructions, data structures, program
modules, or other data.
[0035] The modules and data 304 can be utilized by the
telecommunication device 102 to perform or enable performing any
action taken by the telecommunication device 102. The modules and
data 304 can include a telecommunication device platform and
applications, and data utilized by the platform and
applications.
[0036] In some examples, the processor(s) 306 is a central
processing unit (CPU), a graphics processing unit (GPU), or both
CPU and GPU, or any other sort of processing unit.
[0037] The radio interfaces 308 can include transceivers, modems,
interfaces, and/or other components that perform or assist in
exchanging radio frequency (RF) communications with a base station
104 via transmitter and receiver antennas 114. By way of a
non-limiting example, a telecommunication device's radio interfaces
308 can include an RF Front End (RFFE) that receives RF signals via
four receiving antennas 114 in a 4.times.4 MIMO configuration, an
RFIC (RF Integrated Chip) that decodes the RF signals into four
data streams 106, and a modem that performs other processing
operations on the data streams 106. In other examples a processor
306, other modules and data 304, and/or other components of the
telecommunication device 102 can perform or assist in transmitting
and/or receiving data via the antennas 114, and/or pre-processing
or post-processing of such data.
[0038] In various examples, the display 310 is a liquid crystal
display or any other type of display commonly used in
telecommunication devices 102. For example, display 310 may be a
touch-sensitive display screen, and can then also act as an input
device or keypad, such as for providing a soft-key keyboard,
navigation buttons, or any other type of input.
[0039] In some examples, the output devices 312 can include any
sort of output devices known in the art, such as a display 310,
speakers, a vibrating mechanism, and/or a tactile feedback
mechanism. Output devices 312 can also include ports for one or
more peripheral devices, such as headphones, peripheral speakers,
and/or a peripheral display.
[0040] In various embodiments, input devices 314 can include any
sort of input devices known in the art. For example, input devices
314 can include a microphone, a keyboard/keypad, and/or a
touch-sensitive display, such as the touch-sensitive display screen
described above. A keyboard/keypad can be a push button numeric
dialing pad, a multi-key keyboard, or one or more other types of
keys or buttons, and can also include a joystick-like controller,
designated navigation buttons, or any other type of input
mechanism.
[0041] The machine readable medium 318 can store one or more sets
of instructions, such as software or firmware, that embodies any
one or more of the methodologies or functions described herein. The
instructions can also reside, completely or at least partially,
within the memory 302, processor(s) 306, and/or radio interface(s)
308 during execution thereof by the telecommunication device 102.
The memory 302 and the processor(s) 306 also can constitute machine
readable media 322.
Example Operations
[0042] FIG. 4 depicts a flow chart of a method for increasing
throughput to a telecommunication device by inducing a base station
104 to transmit additional data streams 106 using MIMO
techniques.
[0043] At block 400, the telecommunication device 102 can receive
RF signals from the base station 104 using multiple receiver
antennas 114.
[0044] At block 402, the telecommunication device 102 can decode
the received RF signals into one or more data streams 106. For
example, the telecommunication device 102 can de-multiplex the
received RF signals to distinguish different data streams 106 sent
over the same radio channel. In some cases the telecommunication
device 102 may not be able to successfully decode all of the data
streams 106 sent by the base station 104, such as when there is
noise or interference due to multipath propagation of the MIMO
signals, or other issues that affect the signals received by the
telecommunication device. During or following decoding, the
telecommunication device 102 can also determine an error rate 200
of the decoded data. For example, the error rate 200 can be
measured as a downlink Block Error Rate (DL BLER), the percentage
of the total number of data blocks that CRC codes indicate have an
error.
[0045] At block 404, the telecommunication device 102 can count the
number of data streams 106 that were decoded during block 402. The
telecommunication device 102 can then determine whether the number
of different data streams 106 decoded from the received RF signals
is equal to a maximum RI for the MIMO arrangement of the
telecommunication device 102 and base station 104. As discussed
above, the maximum RI can be the maximum number of data streams 106
that could be transmitted from the base station 104 to the
telecommunication device 102, as limited by the number of
transmitter antennas 114 in the base station 104 and/or the number
of receiver antennas 114 in the telecommunication device 102.
[0046] For example, if the telecommunication device 102 has four
receiver antennas 114 and a base station 104 is capable of sending
four data streams 106 to those four receiver antennas 114 in a
4.times.4 MIMO configuration, the maximum RI can be set to four and
the telecommunication device 102 can determine at block 404 whether
or not it decoded four data streams 106 from the received RF
signals. In other examples the maximum RI can be set to any other
value limited by the number of antennas 114 at the
telecommunication device 102 and/or base station 104, and the
telecommunication device 102 can check at block 404 if it decoded a
number of data streams 106 equal to that maximum RI.
[0047] If the telecommunication device 102 determines at block 404
that it decoded a number of data streams 106 equal to the maximum
RI, it can set the value of an RI 110 to the maximum RI at block
406. For example, if the maximum RI is four and the
telecommunication device 102 decoded four data streams 106, it can
set the RI to "4." The RI 110 can be reported to the base station
104 at block 414, as will be discussed below.
[0048] However, if the telecommunication device 102 determines that
it decoded a number of data streams 106 that is less than the
maximum RI, at block 408 it can set the value of the RI 110 to the
number of decoded data streams 106 and then move to block 410. For
example, if the maximum RI is four, but the telecommunication
device 102 decoded only three data streams, it can set the RI 110
to "3."
[0049] If the telecommunication device 102 did not set the RI 110
to the maximum RI, at block 410 the telecommunication device 102
can determine if the error rate 200 of the decoded data is below an
RI increase threshold 204. As shown in FIG. 2, the RI increase
threshold 204 can be less than or equal to the acceptable error
rate 202. For example, when the acceptable error rate 202 is set to
a DL BLER of 10%, the RI increase threshold 204 can be set to a DL
BLER of 10%, or to any lower percentage, such as 8%.
[0050] If the error rate 200 of the decoded data is found during
block 410 to be above the RI increase threshold 204, the
telecommunication device 102 can maintain the value of the RI 110
set during block 408 and move to block 414 to report the RI 110 to
the base station 104. For example, if the acceptable error rate 202
is a BLER of 10% and the RI increase threshold 204 is set to a BLER
of 6%, when the error rate 200 is found to be a BLER of 9% the
original RI 110 value can be maintained even though the error rate
200 is below the acceptable error rate 202.
[0051] However, if the error rate 200 of the decoded data is found
during block 410 to be at or below the RI increase threshold 204,
the telecommunication device 102 can increase the value of the RI
110 from the value set during block 408. The RI 110 can be
increased by any desired amount, up to the maximum RI. For example,
if the maximum RI is four but the RI 110 was set to "3" during
block 408 because only three data streams were decoded, when the
error rate 200 is below the RI increase threshold 204 the RI 110
can be increased to "4" at block 412. The telecommunication device
102 can then report this increased RI 110 to the base station 104
at block 414.
[0052] At block 414, the telecommunication device 102 can send a
report 108 to the base station 104 that includes the RI 110 set
using the process of FIG. 4. In some examples the telecommunication
device 102 can also include a CQI 112 in the report 108. As
described above, the telecommunication device 102 can use the
measured error rate 200 to also determine the CQI 112. For example,
the telecommunication device 102 can determine the DL BLER in
received data and then report a CQI 112 value associated with an
MCS that is expected to lead to a DL BLER under a predefined
acceptable error rate 202, such as a BLER of 10%. In some examples
the report 108 can include the measured error rate 200 in place of,
or in addition to, the CQI 112.
[0053] After the base station 104 receives the report 108, the base
station 104 can use the reported RI 110 to determine the number of
data streams 106 to transmit to the telecommunication device 102
using MIMO techniques during future transmissions. The base station
104 can also use the reported CQI 112 and/or error rate 200 to
determine an MCS to use when sending data during future
transmissions.
[0054] In situations in which the telecommunication device inflated
the reported RI 110 beyond what it otherwise would have reported,
because the error rate 200 was found during block 410 to be lower
than an RI increase threshold 204, the base station 104 can follow
the reported RI 110 and next attempt to send a corresponding number
of data streams using MIMO techniques. The telecommunication device
102 can thus adaptively induce the base station 104 to send a
higher number of data streams 106 than would otherwise be sent,
thereby increasing the data throughput to the telecommunication
device 102.
[0055] For example, when the base station 104 had been sending
three data streams 106 but the telecommunication device 102 sends
an RI 110 of "4" because the error rate 200 was found to be lower
than the RI increase threshold 204 during block 410, the reported
RI 110 can trigger the base station 104 to begin sending in
4.times.4 MIMO mode, thereby increasing throughput to the
telecommunication device 102.
[0056] Because the error rate 200 would also be lower than the
acceptable error rate 202 in this example, the telecommunication
device 110 can also report a high CQI 112 associated with a good
MCS that can also increase throughput to the telecommunication
device 102. For example, when the reported RI 110 is "4" and the
reported CQI 112 is high and associated with an MCS that uses
256-QAM, the report 108 can induce the base station 104 to begin
sending in 4.times.4 MIMO mode using 256-QAM, both of which can
increase throughput to the telecommunication device 102.
[0057] Inducing the base station 104 to send additional data
streams 106 may result in an increase in the measured error rate
200. However, in many situations the additional data stream 106 can
be received and decoded by the telecommunication device 102 without
the error rate 200 going over the acceptable error rate 202. For
example, when the measured error rate 200 is a DL BLER of 2% and
the acceptable error rate 202 is a DL BLER of 10%, increasing the
RI 110 to induce the base station 104 to send an additional data
stream 106 might result in the error rate 200 increasing to a DL
BLER of 8% or other percentage that is still below the acceptable
error rate 202.
[0058] Following sending a report 108 with an increased RI 110, the
telecommunication device 102 can monitor the error rate 200, and
then drop the RI 110 back to non-increased levels if the error rate
200 goes over the acceptable error rate 202. For example, following
sending a report 108 with an increased RI 110 at block 414, the
telecommunication device 102 can return to block 400. If the
telecommunication device 102 cannot decode a number of data streams
106 equal to the increased RI 110 at block 404, the RI 110 can be
set to the number of decodable data streams 106 at block 408.
Because the error rate 200 exceeded the RI increase threshold 204
in this example, the telecommunication device 102 would not move to
block 412 to increase the RI 110 again, and the lower RI 110 would
be reported at block 414.
CONCLUSION
[0059] Although the subject matter has been described in language
specific to structural features and/or methodological acts, it is
to be understood that the subject matter is not necessarily limited
to the specific features or acts described above. Rather, the
specific features and acts described above are disclosed as example
embodiments.
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