U.S. patent application number 16/265036 was filed with the patent office on 2020-08-06 for self-optimizing network for narrowband internet-of-things in-band deployment modes.
The applicant listed for this patent is Cisco Technology, Inc.. Invention is credited to Mark Grayson, Santosh Ramrao Patil, Gangadharan Byju Pularikkal, Akram Ismail Sheriff.
Application Number | 20200252809 16/265036 |
Document ID | 20200252809 / US20200252809 |
Family ID | 1000003896228 |
Filed Date | 2020-08-06 |
Patent Application | download [pdf] |
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United States Patent
Application |
20200252809 |
Kind Code |
A1 |
Patil; Santosh Ramrao ; et
al. |
August 6, 2020 |
SELF-OPTIMIZING NETWORK FOR NARROWBAND INTERNET-OF-THINGS IN-BAND
DEPLOYMENT MODES
Abstract
Techniques for optimizing performance of narrowband
Internet-of-Things (NB-IoT) devices in a wireless wide area network
(WWAN) are described. In one embodiment, a method includes
providing a NB-IoT base station in an in-band deployment mode to
operate within a WWAN. The NB-IoT base station is configured to use
a physical resource block of the WWAN for communicating with a
plurality of NB-IoT devices. The method includes causing a
reduction of a power level for a transmission from an initial power
level to a first reduced power level. The method includes obtaining
parameters associated with performance and throughput for the WWAN
and comparing the parameters to a quality threshold. Based on the
comparison of the parameters to the threshold, the method includes
determining whether or not to reduce the power level for the
physical resource block from the first reduced power level to a
second reduced power level.
Inventors: |
Patil; Santosh Ramrao;
(Santa Clara, CA) ; Grayson; Mark; (Berkshire,
GB) ; Pularikkal; Gangadharan Byju; (San Jose,
CA) ; Sheriff; Akram Ismail; (San Jose, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Cisco Technology, Inc. |
San Jose |
CA |
US |
|
|
Family ID: |
1000003896228 |
Appl. No.: |
16/265036 |
Filed: |
February 1, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04W 24/02 20130101;
H04W 52/36 20130101; H04W 16/14 20130101; H04W 52/265 20130101;
H04W 72/121 20130101; H04W 52/247 20130101 |
International
Class: |
H04W 24/02 20060101
H04W024/02; H04W 16/14 20060101 H04W016/14; H04W 52/36 20060101
H04W052/36; H04W 52/24 20060101 H04W052/24; H04W 52/26 20060101
H04W052/26; H04W 72/12 20060101 H04W072/12 |
Claims
1. A method comprising: providing a narrowband Internet-of-Things
(NB-IoT) base station in an in-band deployment mode to operate
within a wide area wireless network (WWAN), wherein the NB-IoT base
station is configured to use a physical resource block of the WWAN
for communicating with a plurality of NB-IoT devices, wherein the
plurality of NB-IoT devices are identified based on at least a
detected repetition rate on a physical random access channel of a
transmission made by a device of the plurality of NB-IoT devices,
and wherein the plurality of NB-IoT devices are grouped to the
physical resource block of the WWAN; causing, by the NB-IoT base
station, a reduction of a power level of the NB-IoT base station
for a transmission using the physical resource block from an
initial power level to a first reduced power level; obtaining, by
the NB-IoT base station, parameters associated with performance and
throughput for the WWAN and for the NB-IoT base station; comparing,
by the NB-IoT base station, the parameters to a quality threshold;
and based on the comparing of the parameters to the quality
threshold, determining, by the NB-IoT base station, whether or not
to reduce the power level for the physical resource block from the
first reduced power level to a second reduced power level.
2. The method of claim 1, wherein causing the reduction of the
power level for the physical resource block is performed in one or
more step decreases of a predetermined amount.
3. The method of claim 1, further comprising: upon determining to
reduce the power level from the first reduced power level to the
second reduced power level, obtaining, by the NB-IoT base station,
updated parameters associated with performance and throughput for
the WWAN based on the second reduced power level; and comparing, by
the NB-IoT base station, the updated parameters to the quality
threshold.
4. The method of claim 1, wherein upon determining that the
parameters are below the quality threshold, changing, by the NB-IoT
base station, the power level for the physical resource block from
the first reduced power level back to the initial power level.
5. (canceled)
6. The method of claim 1, wherein identifying the plurality of
NB-IoT devices includes monitoring Signal-Information Blocks in the
transmission made by an NB-IoT device of the plurality of NB-IoT
devices.
7. The method of claim 1, wherein the NB-IoT base station shares
resources with a base station for the WWAN.
8. One or more non-transitory computer readable storage media
encoded with instructions that, when executed by a processor of a
narrowband Internet-of-Things (NB-IoT) base station operating in an
in-band deployment mode within a wide area wireless network (WWAN),
cause the processor to: reduce a power level of the NB-IoT base
station for a physical resource block of the WWAN used for
communicating with a plurality of NB-IoT devices from an initial
power level to a first reduced power level, wherein the plurality
of NB-IoT devices are identified based on at least a detected
repetition rate on a physical random access channel of a
transmission made by a device of the plurality of NB-IoT devices,
and wherein the plurality of NB-IoT devices are grouped to the
physical resource block of the WWAN; obtain parameters associated
with performance and throughput for the WWAN and for the NB-IoT
base station; compare the parameters to a quality threshold; and
based on the compare of the parameters to the quality threshold,
determine whether or not to reduce the power level for the physical
resource block from the first reduced power level to a second
reduced power level.
9. The one or more non-transitory computer readable storage media
of claim 8, wherein reducing the power level for the physical
resource block is performed in one or more step decreases of a
predetermined amount.
10. The one or more non-transitory computer readable storage media
of claim 8, wherein the instructions further cause the processor
to: upon determining to reduce the power level from the first
reduced power level to the second reduced power level, obtain
updated parameters associated with performance and throughput for
the WWAN based on the second reduced power level; and compare the
updated parameters to the quality threshold.
11. The one or more non-transitory computer readable storage media
of claim 8, wherein the instructions further cause the processor
to: upon determining that the parameters are below the quality
threshold, change the power level for the physical resource block
from the first reduced power level back to the initial power
level.
12. (canceled)
13. The one or more non-transitory computer readable storage media
of claim 8, wherein identifying the plurality of NB-IoT devices
includes monitoring Signal-Information Blocks in the transmission
made by an NB-IoT device of the plurality of NB-IoT devices.
14. The one or more non-transitory computer readable storage media
of claim 8, wherein the NB-IoT base station shares resources with a
base station for the WWAN.
15. An apparatus comprising: a transceiver configured to transmit
and receive signals in a wireless wide area network (WWAN); a modem
coupled to the transceiver and configured to modulate signals and
demodulate signals; a processor coupled to the modem and to the
transceiver, wherein the processor is configured to: reduce a power
level of the transceiver for a physical resource block of the WWAN
used for communicating with a plurality of NB-IoT devices from an
initial power level to a first reduced power level, wherein the
plurality of NB-IoT devices are identified based on at least a
detected repetition rate on a physical random access channel of a
transmission made by a device of the plurality of NB-IoT devices,
and wherein the plurality of NB-IoT devices are grouped to the
physical resource block of the WWAN; obtain parameters associated
with performance and throughput for the WWAN and for the apparatus;
compare the parameters to a quality threshold; and based on the
compare of the parameters to the quality threshold, determine
whether or not to reduce the power level for the physical resource
block from the first reduced power level to a second reduced power
level.
16. The apparatus of claim 15, wherein reducing the power level for
the physical resource block is performed in one or more step
decreases of a predetermined amount.
17. The apparatus of claim 15, wherein the processor is further
configured to: upon determining to reduce the power level from the
first reduced power level to the second reduced power level, obtain
updated parameters associated with performance and throughput for
the WWAN based on the second reduced power level; and compare the
updated parameters to the quality threshold.
18. The apparatus of claim 15, wherein the processor is further
configured to: upon determining that the parameters are below the
quality threshold, change the power level for the physical resource
block from the first reduced power level back to the initial power
level.
19. (canceled)
20. The apparatus of claim 15, wherein the apparatus shares
resources with a base station for the WWAN.
21. The apparatus of claim 15, wherein identifying the plurality of
NB-IoT devices includes monitoring Signal-Information Blocks in the
transmission made by an NB-IoT device of the plurality of NB-IoT
devices.
Description
TECHNICAL FIELD
[0001] This disclosure relates to wireless communication
networks.
BACKGROUND
[0002] The Internet of Things (IoT) generally refers to the devices
and machines embedded with electronics and software enabling these
devices and machines to exchange data over a network (e.g., the
Internet). Narrowband IoT (NB-IoT) is a Low Power Wide Area Network
(LPWAN) radio technology standard developed by 3.sup.rd Generation
Partnership Project (3GPP). NB-IoT has been designed to address use
cases requiring low-throughput, high-delay tolerance, and low-power
transmissions from a large number of deployed NB-IoT devices,
including some battery powered NB-IoT devices. NB-IoT uses a subset
of the frequency spectrum allocated to Long-Term Evolution (LTE),
but is limited to a narrowband of 200 kHz.
[0003] NB-IoT may be implemented in three deployment modes,
including a guard band mode, an in-band mode, and a standalone
mode. Guard band mode uses bandwidth that is reserved in the guard
band of an existing LTE network frequency spectrum. In-band mode
uses a physical resource block in the LTE carrier of an existing
LTE network frequency spectrum. Standalone mode uses a separate 200
kHz carrier outside of the existing LTE network frequency
spectrum.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] FIG. 1 is a diagram illustrating a NB-IoT in-band deployment
mode in a wireless wide area network, according to an example
embodiment.
[0005] FIG. 2A is a flowchart illustrating a technique for a power
boost step down optimization for NB-IoT devices configured in an
in-band deployment mode in a wireless wide area network, according
to an example embodiment.
[0006] FIG. 2B is a diagram depicting a modified HARQ
retransmission process according to an example embodiment.
[0007] FIG. 3 is a diagram illustrating identification of NB-IoT
devices in a wireless wide area network, according to an example
embodiment.
[0008] FIG. 4 is a block diagram illustrating a NB-IoT base station
associated with a wireless wide area network base station,
according to an example embodiment.
[0009] FIG. 5 is a diagram illustrating assignment of groups of
NB-IoT devices in a wireless wide area network based on repetition
rates, according to an example embodiment.
[0010] FIG. 6 is a diagram illustrating assignment of coverage
enhancement levels to groups of NB-IoT devices, according to an
example embodiment.
[0011] FIG. 7 is a diagram illustrating an updated assignment of
coverage enhancement levels to groups of NB-IoT devices, according
to an example embodiment.
[0012] FIG. 8A is a flowchart of a method for dynamic selection of
coverage enhancement level for NB-IoT devices, according to an
example embodiment.
[0013] FIG. 8B is a diagram depicting NB-IoT device detection using
repetition trend count, according to an example embodiment.
[0014] FIG. 9 is a diagram illustrating techniques for physical
resource block selection for NB-IoT devices to optimize
interference in a wireless wide area network, according to an
example embodiment.
[0015] FIG. 10 is a flowchart of a method for selection of a
physical resource block in a wireless wide area network for
optimizing interference from NB-IoT devices, according to an
example embodiment.
[0016] FIG. 11 is a diagram illustrating a roaming scenario for a
NB-IoT device traveling between coverage areas of two different
NB-IoT base stations, according to an example embodiment.
[0017] FIG. 12 is a diagram illustrating a roaming NB-IoT device
traveling to a new NB-IoT base station, according to an example
embodiment.
[0018] FIG. 13 is a flowchart of a method for using a relative
narrowband transmit power information element to optimize power for
a roaming NB-IoT device, according to an example embodiment.
[0019] FIG. 14 is a diagram is a diagram showing a power
consumption transition pattern during a connection phase of a
NB-IoT device, according to an example embodiment.
DESCRIPTION OF EXAMPLE EMBODIMENTS
Overview
[0020] Presented herein are techniques for optimizing performance
of NB-IoT devices configured in an in-band deployment mode in a
wireless wide area network. In an example embodiment, a method
includes providing a NB-IoT base station in an in-band deployment
mode to operate within a wide area wireless network (WWAN). The
NB-IoT base station is configured to use a physical resource block
of the WWAN for communicating with a plurality of NB-IoT devices.
The method also includes causing, by the NB-IoT base station, a
reduction of a power level for a transmission using the physical
resource block from an initial power level to a first reduced power
level. The method includes obtaining, by the NB-IoT base station,
parameters associated with performance and throughput for the WWAN
and comparing, by the NB-IoT base station, the parameters to a
quality threshold. Based on the comparison of the parameters to the
threshold, the method further includes determining, by the NB-IoT
base station, whether or not to reduce the power level for the
physical resource block from the first reduced power level to a
second reduced power level.
Example Embodiments
[0021] Due to the unique characteristics of NB-IoT, there is a need
for specially designed self-optimizing networks (SON) for NB-IoT
deployment optimizations. The techniques described herein provide
SON enhancements for optimizing performance of NB-IoT devices
configured in an in-band deployment mode in a wireless wide area
network.
[0022] 3GPP LTE Release 14 specifications were developed to deliver
enhanced user experience in selected areas through the addition of
features such as increased positioning accuracy, increased peak
data rates, the introduction of a lower device power class,
improved non-anchor carrier operation, multicast, and authorization
of coverage enhancements. However, several problems remain to be
addressed. For example, user equipment (UE) in power saving mode is
not available or immediately reachable for mobile terminating
services. There are many NB-IoT sensors and devices that go into
power saving mode in parking use cases and/or if they are not able
to terminate an IoT service with a mobile NB-IoT base station.
Additionally, radio resource management and optimization for NB-IoT
devices in a SON for different types of UEs with different coverage
enhancement levels are not covered by the 3GPP Release 14
specifications.
[0023] The techniques of the example embodiments described herein
provide several benefits for NB-IoT device deployments, including
providing mobility support for no connected mode, less signaling
traffic and overhead, power save mode during device transmit,
receive, and idle mode operations, and leverage the use of
Narrowband Physical Random Access Channel (NPRACH) for NB-IoT
devices.
[0024] The main challenge in radio resource management and/or SON
for LTE and NB-IoT deployments is that the information used to
control the LTE radio frequency link performance and coverage is
spread across all of the protocol layers, from Signal-Information
Blocks (SIB) in layer 3 (e.g., radio resource control) to the
downlink control information (DCI) content in layer 1 (i.e., the
physical layer) of the LTE stack. To decode and collect this
information from all three of these layers takes processing time
for a 5G high density IoT deployment.
[0025] Existing SON solutions for 3G and LTE networks takes a
snapshot of the network, performs baselining of the network, and
then takes action for optimization of the network. These existing
solutions also typically have a closed loop feedback mechanism to
check the result of the applied action and make decisions whether
to commit to the action and move on, or to revert the changes.
[0026] However, these existing SON optimization solutions are
insufficient for a dense 5G IoT deployment with many NB-IoT devices
and/or sensors that are spread out and competing for radio
resources. Such NB-IoT-based use cases would benefit from a new
approach for SON to handle dense NB-IoT deployments. The
embodiments described herein provide techniques for optimizing
performance of NB-IoT devices configured in an in-band deployment
mode in a wireless wide area network.
[0027] According to the techniques of the present embodiments, a
SON-based radio resource management solution for 5G NB-IoT
deployments may provide several optimizations for NB-IoT-based use
cases, including, but not limited to: power optimization with power
boost step down, coverage enhancement level based optimization,
physical resource block optimization for interference mitigation,
and/or leveraging relative narrowband transmit power (RNTP)
information element (IE) for power optimization for roaming NB-IoT
devices.
[0028] According to the principles of the example embodiments
described herein, techniques for using self-optimizing networks in
a wireless communication network for optimizing NB-IoT in-band
deployment modes scenarios are presented.
[0029] Power Boost Step Down Optimization
[0030] Referring now to FIGS. 1-4, techniques for power
optimization with power boost step down are illustrated, according
to an example embodiment. In a NB-IoT in-band deployment mode
scenario, a NB-IoT base station is anchored in a parent LTE cell
and borrows power from that parent LTE cell to serve all of the
NB-IoT devices. In such in-band deployment mode scenarios, a blind
increase in signal power value results in excess power being
provided to the NB-IoT physical resource block at the expense of
power for the rest of the parent LTE band. This reduction in power
can adversely affect performance of the parent LTE cell where LTE
devices, such as smart phones or mobile clients/devices, are
served, which are already in a connected mode, thereby resulting in
a reduction of throughput at the parent LTE cell edge.
[0031] FIG. 1 is a diagram illustrating an environment 100 in which
techniques for power optimization with power boost step down may be
implemented according to an example embodiment. In one embodiment,
environment 100 includes a plurality of user devices, including one
or more wireless user devices and one or more NB-IoT devices.
Examples of plurality of user devices may include, but are not
limited to: mobile devices, cell phones, tablets, printers,
computers, consumer electronics, NB-IoT devices, IoT devices, as
well as other devices that include equipment to establish a
connection with a WWAN. In this embodiment, the one or more
wireless user devices include at least a first wireless user device
101, a second wireless user device 102, and a third wireless user
device 103. The one or more NB-IoT devices include at least a first
NB-IoT device 104, a second NB-IoT device 105, and a third NB-IoT
device 106. It should be understood that environment 100 may
include additional user devices, including additional wireless user
devices and/or NB-IoT devices.
[0032] In this embodiment, environment 100 includes a wireless wide
area network base station 110 for a wireless wide area network
(WWAN). In some embodiments, the WWAN may be configured in
compliance with 4.sup.th generation (4G), Long-Term Evolution
(LTE), and/or 5.sup.th generation (5G) wireless wide area network
specifications. Additionally, environment 100 includes a NB-IoT
base station 120 (e.g., an eNodeB or "eNB") that is anchored to
WWAN base station 110. In an example embodiment, NB-IoT base
station 120 may share radio resources, such as RF transceivers 112,
with WWAN base station 110.
[0033] As described above, in the example embodiments described
herein, NB-IoT base station 120 and a plurality of NB IoT devices
(e.g., first NB-IoT device 104, second NB-IoT device 105, and third
NB-IoT device 106) are configured in an in-band deployment mode
with the WWAN. Accordingly, in this in-band deployment mode, NB-IoT
base station 120 uses a physical resource block (PRB) 116 in the
carrier of a frequency spectrum 114 allocated to the WWAN network
for communicating with the plurality of NB-IoT devices 104, 105,
106.
[0034] In this embodiment, plurality of NB-IoT devices 104, 105,
106 are connected to PRB 116 of WWAN through NB-IoT base station
120, which allows any of these devices to communicate with remote
servers, for example, NB-IoT application services 132 or other
destinations, via the Internet outside of a core network 130 of the
WWAN.
[0035] In an example embodiment, NB-IoT base station 120 uses
channel feedback from NB-IoT devices (e.g., plurality of NB-IoT
devices 104, 105, 106) to determine modulation and coding scheme
allocations. Each NB-IoT device reports Hybrid Automatic Repeat
Requests (HARQ) feedback and Channel Quality Indicator (CQI) values
to NB-IoT base station 120 using a Physical Uplink Control Channel
(PUCCH) or Physical Uplink Shared Channel (PUSCH). In some cases,
each downlink HARQ process may have variable timing. NB-IoT base
station 120 can begin transmitting to one or more NB-IoT devices
(e.g., plurality of NB-IoT devices 104, 105, 106) as soon as it
receives the acknowledgements (i.e., ACK/NACK) from the NB-IoT
devices, depending on availability of PRB 116.
[0036] According to the techniques presented herein, a power
optimization mechanism is provided to minimize the effect of NB-IoT
base station 120 on its parent WWAN cell (e.g., WWAN base station
110) and neighboring cells by adjusting a power boost to optimize
an amount of excess power on the NB-IoT PRB (e.g., PRB 116). HARQ
NACKs, as described above, result in retransmissions, and in a
high-density NB-IoT deployment (e.g., environment 100, shown in
FIG. 1), these retransmissions will consume more WWAN airtime. Such
retransmissions can affect a mission critical sensor in receiving
control signals in a downlink direction to transmit a payload. As
part of the power optimization mechanism presented herein, the
NB-IoT power boost can be moved to the lowest value on the NB-IoT
base station (e.g., NB-IoT base station 120) so that a maximum
desired maximum coupling loss (MCL) of 164 dB for a NB-IoT device
is achieved.
[0037] Referring now to FIG. 2A, a flowchart illustrating a method
200 for a power boost step down optimization mechanism for NB-IoT
devices configured in an in-band deployment mode in a wireless wide
area network is shown according to an example embodiment. In some
embodiments, method 200 may be implemented by a NB-IoT base station
(e.g., NB-IoT base station 120). In this embodiment, method 200
includes an operation 202 where an initial power level is
established for a PRB allocated for the NB-IoT deployment (e.g.,
PRB 116, as shown in FIG. 1 above).
[0038] Next, method 200 includes an operation 204 where a power
level for the PRB is reduced from the initial power level
established at operation 202. In one embodiment, the initial power
level may be reduced by a predetermined amount to a first reduced
power level. For example, power boost levels for a PRB may be
reduced in one or more step decreases of a predetermined amount,
which may be based on a pre-allocated map or lookup table stored at
the NB-IoT base station.
[0039] After each step decrease of power boost level reduction
(i.e., after each iteration of operation 204), closed loop feedback
may be checked with the parent WWAN cell (e.g., WWAN base station
110) for effects on performance and throughput as compared with the
child NB-IoT cell's performance (e.g., NB-IoT base station 120).
For example, method 200 includes an operation 206 wherein
performance and throughput parameters are obtained for the WWAN
cell and NB-IoT cell. At an operation 208, the parameters obtained
at operation 206 are compared to a quality threshold. For example,
the quality threshold at operation 208 may be associated with RF
link characteristics, so that operation 208 analyzes the
degradation effects from the step down in power level at the RF
link level.
[0040] At operation 208, whether or not the parameters are less
than the quality threshold is determined. Upon determining at
operation 208 that the parameters are not less than the quality
threshold (i.e., the degradation at the RF link level is still
within an acceptable value), then method 200 proceeds back to
operation 204. At operation 204, another step down decrease in the
power level for the PRB may be performed (e.g., reducing power
level from the first reduced power level to a second reduced power
level), and the effects of that reduction evaluated again at
operation 206, where updated parameters associated with performance
and throughput are obtained based on the further reduced power
level and evaluated against the quality threshold at operation
208.
[0041] Upon determining at operation 208 that the parameters are
less than the quality threshold (i.e., the degradation at the RF
link level has fallen below an acceptable value), then method 200
may proceed to an operation 210. At operation 210, the last change
to the power levels for the PRB are reverted (i.e., changed back to
the previous power level). With this arrangement, method 200 allows
the NB-IoT base station to adaptively determine whether to make
additional decreases in power boost levels or to revert the last
iteration of changes to the previous level.
[0042] These techniques for power optimization with power boost
step down provided by method 200 clear more power resources for a
parent WWAN cell (e.g., WWAN base station 110) and improves its
performance. Additionally, this mechanism for power boost
optimization also reduces interference on the PRB (e.g., PRB 116)
allocated to the NB-IoT in-band deployment with the other bands
within the WWAN (e.g., WWAN 114) serving the wireless user devices
(e.g., plurality of wireless user devices 101, 102, 103). Method
200 is able to provide harmonious co-existence of the traditional
WWAN bands and the NB-IoT deployment.
[0043] Turning to FIG. 2B, a diagram is shown of a modified HARQ
retransmission process according to an example embodiment. HARQ
Negative Acknowledgements (NACKs) result in retransmissions. In a
high density IoT deployment, many such retransmissions will consume
more air time which can affect a mission critical sensor in
receiving a control signal sent in the downlink direction to
transmit a payload. In FIG. 2B, the top line represents a NB-IoT
base station and the bottom line represents a NB-IoT device or a
user device. In FIG. 2B, P1 represents a transmission attempt for a
first packet from the NB-IoT base station, P2 represents a
transmission attempt for a second packet from the NB-IoT base
station, P3 represents a transmission attempt for a third packet.
P2.1 represents a second transmission attempt of the second packet
P2 and P2.2 represents a third transmission attempt of second
packet P2. In general, HARQ can have a maximum of 4
transmission.
[0044] In FIG. 2B, packet P1 transmitted at 230 from the NB-IoT
base station, and it is received normally and stored at the NB-IoT
device or user device. At 234, an ACK is sent to the NB-IoT base
station. At 240, the NB-IoT device transmits packet P2 and it is
not successfully received by the NB-IoT device or user device. At
242, whatever portion of packet P2 that was successfully received
is stored in a HARQ buffer at the NB-IoT device or user device. At
244, the NB-IoT device or user device ends a NACK to the NB-IoT
base station. At 250, the NB-IoT base station retransmits packet P2
(referred to as P2.1). At 252, whatever portion of packet P2.1 that
was successfully received at the NB-IoT device or user device is
stored in its HARQ buffer. At 254, the NB-IoT device or user device
sends a NACK to the NB-IoT base station. At 260, the NB-IoT base
station transmits packet P2 again (referred to as P2.2). At 262,
the NB-IoT device or user device stores packet P2.2. At 264, the
NB-IoT device or user device sends an ACK to the NB-IoT base
station.
[0045] User devices and NB-IoT devices handled by the same base
station are classified, and the HARQ retry transmission count is
changed. As a result, for example:
[0046] P1+P1.1=P1 meaning packet P1 is a derived based on a
combination of P1 and P1.1. In the example of FIG. 2B, there is no
P1.1 because P1 was received successfully at 230 and 232.
[0047] P2+P2.1=P2 meaning packet P2 is based on a combination of P2
and P2.2.
[0048] P2+P2.1+P2.2=P2 meaning packet P2 is based on a combination
of P2, P2.1 and P2.2.
[0049] In some embodiments, NB-IoT devices in an in-band deployment
mode may be identified and grouped together so that the
optimizations described herein may be applied to the group of
NB-IoT devices as a whole. For example, method 200 may be applied
to reduce the power levels for the PRB assigned to a group of
NB-IoT devices. Referring now to FIG. 3, a diagram illustrating
identification of NB-IoT devices 104, 105, 106 in the WWAN is shown
according to an example embodiment.
[0050] In some embodiments, a transmission on a physical random
access channel (PRACH) may be used to differentiate NB-IoT devices
(e.g., plurality of NB-IoT devices 104, 105, 106) from other
wireless user devices in environment 100 (e.g., plurality of
wireless user devices 101, 102, 103) based on the repetition rate
of the PRACH transmission. For example, NB-IoT devices have a
repetition rate for the PRACH transmission from 1, 2, 4, up to 128
times maximum in the uplink direction. Repetitive transmissions
from an NB-IoT device (e.g., plurality of NB-IoT devices 104, 105,
106) are performed for almost every channel. However, for other
devices (e.g., plurality of wireless user devices 101, 102, 103),
only time and interval bundling is an intentional repetitive
transmission, all other transmissions are intended for single
repetition only and not multiple repetitions.
[0051] In some embodiments, a SON agent associated with NB-IoT base
station 120 can monitor and analyze a repetition rate of
transmissions made on the PRACH. Depending on the determined
repetition rate on the PRACH, a NB-IoT device can be differentiated
from other wireless user devices. That is, if a repetition rate of
at least one and up to 128 is determined for a PRACH transmission,
then a device of plurality of NB-IoT devices 104, 105, 106 is
identified as an NB-IoT device. The identified NB-IoT devices may
then be associated in a group 300. For example, as shown in FIG. 3,
group 300 includes first NB-IoT device 104, second NB-IoT device
105, and third NB-IoT device 106.
[0052] In one embodiment, identifying the plurality of NB-IoT
devices 104, 105, 106 includes monitoring Signal-Information Blocks
in the PRACH transmission made by a device of plurality of NB-IoT
devices 104, 105, 106. In another embodiment, identifying the
plurality of NB-IoT devices 104, 105, 106 may also be based on a
coverage enhancement level used for an application session between
a NB-IoT device and the NB-IoT base station determined during the
random access channel (RACH) transmission phase.
[0053] According to the techniques described herein, the NB-IoT
device grouping is based on channel feedback calculation and
sending the channel feedback to the NB-IoT base station (e.g.,
NB-IoT base station 120). Additionally, grouping of NB-IoT devices
(e.g., group 300) may be based on Signal-Information Blocks and/or
coverage enhancement levels.
[0054] FIG. 4 illustrates an example block diagram of a NB-IoT base
station (e.g., NB-IoT base station 120) anchored to a parent WWAN
cell (e.g., WWAN base station 110) that may be configured to
implement techniques for optimizing performance of NB-IoT devices
configured in an in-band deployment mode in a wireless wide area
network, according to the principles of the embodiments described
herein.
[0055] In some embodiments, NB-IoT base station 120 may be anchored
to WWAN base station 110 and may share radio resources with WWAN
base station 110. For example, NB-IoT base station 120 and WWAN
base station 110 may share RF transceiver(s) 112. WWAN base station
110 may have multiple antennas and RF transceiver 112 may have
multiple transmitters and receivers, one for each antenna. RF
transceiver 112 performs down converting to baseband of received
radio frequency signals and up converting to radio frequency of
baseband transmit signals.
[0056] In this embodiment, WWAN base station 110 may include a
baseband processor (modem) 400, a controller (microprocessor or
microcontroller) 402, a network interface 404, and a memory 406
that stores instructions for control logic 408. The baseband
processor 400 performs baseband modulation to produce baseband
transmit signals and baseband demodulation of received baseband
receive signals. The baseband processor 400 may also perform
various media access control (MAC) functions. The RF transceiver
112 and baseband processor 400 may be embodied as part of
integrated circuit (IC) chipsets that are compliant with IEEE
802.11, for example. In some embodiments, NB-IoT base station 120
may also share functions of baseband processor 400 with WWAN base
station 110.
[0057] Controller 402 performs higher-level control of WWAN base
station 110 and to this end executes instructions for the control
logic 408 stored in memory 406. The network interface 404 is a
network interface card (NIC) that enables wired network
communication via a LAN (not shown) or other network connections.
Control logic 408 may be configured to implement one or more
conventional functions of WWAN base station 110 for operation of
the WWAN.
[0058] In this embodiment, NB-IoT base station 120 may include a
controller (microprocessor or microcontroller) 410, a network
interface 412, and a memory 414 that stores instructions for
control logic 416 and SON agent logic 418. In some embodiments,
NB-IoT base station 120 may also share functions of baseband
processor 400 with WWAN base station 110. Controller 410 performs
higher-level control of NB-IoT base station 120 and to this end
executes instructions for control logic 416 stored in memory 414.
The network interface 412 is a network interface card (NIC) that
enables wired network communication via a LAN (not shown) or other
network connections. Control logic 416 may be configured to
implement one or more functions of NB-IoT base station 120. In some
embodiments, SON agent logic 418 is configured to implement one or
more operations associated with the techniques for optimizing
performance of NB-IoT devices configured in an in-band deployment
mode in a wireless wide area network described herein, including
operations associated with the techniques of the present
embodiments described in reference to FIGS. 1-3 above, as well as
FIGS. 5-13 described in detail below.
[0059] Dynamic Selection of Coverage Enhancement Level
[0060] Referring now to FIGS. 5-8, techniques for coverage
enhancement level based optimization of NB-IoT devices configured
in an in-band deployment mode in a wireless wide area network are
provided. For coverage purposes, NB-IoT specifications include the
concept of coverage enhancement levels. Coverage enhancement is
achieved not by raising power levels of transmitter antennas of a
NB-IoT base station, but instead by advantageously combining
transmission repetitions.
[0061] Three coverage enhancement levels are provided, expressed in
terms of maximum coupling loss (MCL) values, including: a coverage
enhancement level 0 (also referred to as "Normal") associated with
a MCL value of 144 dB, a coverage enhancement level 1 (also
referred to as "Robust") associated with a MCL value of 154 dB, and
a coverage enhancement level 2 (also referred to as "Extended")
associated with a MCL value of 164 dB.
[0062] MCL is a common measure to describe an amount of coverage a
WWAN system or other RF system design can support without adversely
affecting performance. MCL is calculated based on four inputs:
device power amplifier power, receiver noise figure (NF), occupied
channel bandwidth, and required signal to noise ratio (SNR) at the
device end point or sensor.
[0063] When sending data to a NB-IoT base station (e.g., NB-IoT
base station 120), some NB-IoT devices use two repetitions, some
use four repetitions, and some use more, as described above. There
are no techniques for optimization in the 3GPP Release 14
specifications for dynamically fixing an NRSRP threshold base on a
polling repetition count by a NB-IoT device. The techniques for
coverage enhancement level based optimization of NB-IoT devices
provided herein leverage repetition rates for one or more groups of
NB-IoT devices to improve coverage enhancement levels.
[0064] FIG. 5 is a diagram illustrating assignment of groups of
NB-IoT devices in a wireless wide area network environment 500
based on repetition rates, according to an example embodiment. In
an example embodiment, environment 500 is a NB-IoT in-band
deployment within a WWAN, for example, the WWAN described above in
reference to FIG. 1. In this embodiment, environment 500 includes
NB-IoT base station 120 anchored to WWAN base station 110,
including shared RF transceiver 112. Additionally, environment 500
includes a plurality of NB-IoT devices in communication with NB-IoT
base station 120.
[0065] As described above, a repetition rate of transmissions made
on the PRACH by one or more of the plurality of NB-IoT devices may
be monitored and analyzed. Using these obtained repetition rates,
one or more NB-IoT devices with the same repetition rates may be
grouped together. As shown in FIG. 5, a first device group 501 of
NB-IoT devices are associated with a first repetition rate. In this
embodiment, first device group 501 includes a first NB-IoT device
503, a second NB-IoT device 505, and a third NB-IoT device 507.
Similarly, a second device group 502 of NB-IoT devices are
associated with a second repetition rate that is different than the
first repetition rate. In this embodiment, second device group 502
includes a fourth NB-IoT device 504, a fifth NB-IoT device 506, and
a sixth NB-IoT device 508.
[0066] In an example embodiment, techniques for coverage
enhancement level based optimization of NB-IoT devices take
advantage of the same repetition rates shared by all NB-IoT devices
in the same device groups (e.g., first device group 501 and second
device group 502) to improve coverage enhancement levels for the
NB-IoT devices. Referring now to FIG. 6, a diagram 600 illustrating
the three coverage enhancement levels, as described above, is
shown. In this embodiment, diagram 600 shows the relationship
between received power level along a first axis 601 and a path loss
(measured in dBm) along a second axis 602. The three coverage
enhancement levels include a Normal enhancement level 610
associated with a MCL value of 144 dB, a Robust coverage
enhancement level 620 associated with a MCL value of 154 dB, and an
Extended coverage enhancement level 630 associated with a MCL value
of 164 dB.
[0067] As illustrated in diagram 600, received power level along
first axis 601 decreases relative to increasing path loss along
second axis 602, i.e., from Normal enhancement level 610 to Robust
coverage enhancement level 620 to Extended coverage enhancement
level 630. The assigned coverage enhancement level determines the
Narrowband Physical Random Access Channel (NPRACH) resources that
are allocated to a device, including: subset of subcarriers, PRACH
repetitions, maximum number of attempts a device may make. User
equipment (i.e., wireless user devices and/or NB-IoT devices)
derive their assigned coverage enhancement levels based on
Narrowband Reference Signal Received Power (NRSRP) threshold value
measurements. According to the 3GPP release 14 specifications,
these NRSRP threshold values are static. For example, as shown in
FIG. 6, a first threshold value 604 (NRSRP1) separates Normal
enhancement level 610 from Robust coverage enhancement level 620.
Additionally, a second threshold value 606 (NRSRP2) separates
Robust coverage enhancement level 620 from Extended coverage
enhancement level 630.
[0068] As shown in FIG. 6, upon selection of an initial physical
resource block, coverage enhancement levels may be selected for one
or more groups of devices. In this embodiment, measurements of
NRSRP values are obtained for first device group 501 and second
device group 502 based on the selection of the initial physical
resource block of the WWAN spectrum (e.g., WWAN 114 shown in FIG.
1). Based on these NRSRP values, each device group is assigned to a
coverage enhancement level. For example, if the measured NRSRP
value is smaller than first threshold value 604 (NRSRP1) and
smaller than second threshold value 606 (NRSRP2), then Normal
enhancement level 610 is assigned. If the measured NRSRP value is
between first threshold value 604 (NRSRP1) and second threshold
value 606 (NRSRP2), then Robust coverage enhancement level 620 is
assigned. Finally, if the measured NRSRP value is greater than
second threshold value 606 (NRSRP2), then Extended coverage
enhancement level 630 is assigned.
[0069] Based on the selection of the initial physical resource
block, device groups are assigned to their coverage enhancement
levels. In this embodiment, according to a first assignment, first
device group 501 of NB-IoT devices is assigned to Normal
enhancement level 610, a second device group 502 of NB-IoT devices
is assigned to Robust coverage enhancement level 620 and a third
NB-IoT group 510 is assigned to the Extended coverage enhancement
level 630. Additionally, in a WWAN that includes other devices, for
example, one or more wireless user devices as shown in FIG. 1, one
or more groups of wireless user devices may also be assigned to
coverage enhancement levels. For example, in this embodiment, a
first wireless user device group 603 is assigned to Normal
enhancement level 610, a second wireless user device group 605 is
assigned to Robust enhancement level 620, and a third wireless user
device group 607 is assigned to Extended coverage enhancement level
630. In one form, the wireless user device groups may be groups of
LTE-UEs.
[0070] According to the techniques of the example embodiments
described herein, a dynamic selection of coverage enhancement
levels may be implemented by polling a different physical resource
block to obtain an improved NPRACH resource allocation vector.
Based on the device groups (e.g., first device group 501 and second
device group 502), a new physical resource block may be selected
and updated measurements of NRSRP values are obtained. In this
embodiment, upon selection of the new physical resource block of
the WWAN spectrum (e.g., WWAN 114 shown in FIG. 1) updated
measurements of NRSRP values for first device group 501 and second
device group 502 are obtained and used to dynamically change
assignments of coverage enhancement levels.
[0071] Referring now to FIG. 7, diagram 600 is shown illustrating
an updated assignment of coverage enhancement levels to groups of
NB-IoT devices upon selection of a new physical resource block,
according to an example embodiment. Based on the selection of the
new physical resource block, device groups are re-assigned to
coverage enhancement levels. In this embodiment, according to a
second assignment, first device group 501 of NB-IoT devices remains
assigned to Normal enhancement level 610 and the third group 510 of
NB-IoT devices remains assigned to the Extended enhancement level
630. However, second device group 502 of NB-IoT devices is now also
assigned to Normal enhancement level 610. In this embodiment, first
wireless user device group 603, second wireless user device group
605, and third wireless user device group 607 remain assigned
according to the previous assignments shown in FIG. 6.
[0072] With this arrangement, the path loss hysteresis curve can be
polled and monitored based on the new physical resource block
selection to obtain updated NRSRP measurements, which can be
compared to the threshold values (i.e., first threshold value 604
(NRSRP1) and second threshold value 606 (NRSRP2)) to dynamically
improve the assignment of coverage enhancement levels for NB-IoT
device groups. This grouping of NB-IoT devices based on the dynamic
comparison with the NRSRP threshold values can help reduce the
airtime for sending control frames between NB-IoT devices and the
NB-IoT base station. Multiple repetitions can increase the coverage
of a NB-IoT device signal, by optimizing the number of repetitions
needed by device groups, a NB-IoT base station can provide
effective maximum coverage for a cell.
[0073] FIG. 8A is a flowchart of a method 800 for dynamic selection
of coverage enhancement level for NB-IoT devices, according to an
example embodiment. In some embodiments, method 800 may be
implemented by a NB-IoT base station (e.g., NB IoT base station
120). In particular, in some embodiments, method 800 may be
implemented by a SON agent associated with a NB-IoT base
station.
[0074] Method 800 provides techniques for coverage enhancement
level based optimization of NB-IoT devices. In this embodiment,
method 800 begins at an operation 802 where a repetition rate for
one or more NB-IoT devices is monitored or obtained. For example,
as described above, a repetition rate associated with a PRACH
transmission may be determined for a plurality of NB-IoT devices.
Next, at an operation 804, method 800 includes assigning one or
more NB-IoT devices associated with a first repetition rate to a
first device group. For example, as described in reference to FIG.
5 above, first device group 501 associated with a first repetition
rate includes first NB-IoT device 503, second NB-IoT device 505,
and third NB-IoT device 507. At an operation 806, method 800
includes assigning one or more NB-IoT devices associated with a
second repetition rate to a second device group. For example, as
described in reference to FIG. 5 above, second device group 502
associated with a second repetition rate that is different than the
first repetition rate includes fourth NB-IoT device 504, fifth
NB-IoT device 506, and sixth NB-IoT device 508.
[0075] In some embodiments, operations of method 800 associated
with determining and grouping NB-IoT devices into device groups
based on repetition rates (i.e., operations 802, 804, 806) may be
performed as part of other methods described herein. In such
embodiments, one or more NB-IoT devices may already be grouped into
device groups prior to starting method 800.
[0076] Method 800 includes an operation 808, where an initial
physical resource block is selected for communication in the WWAN
by the NB-IoT devices. Next, at an operation 810, measurements of
NRSRP values for the first device group and the second device group
are obtained. For example, as described above with reference to
FIG. 6, NRSRP values for first device group 501 and second device
group 502 may be obtained by NB-IoT base station 120.
[0077] Based on the NRSRP values obtained at operation 810, method
800 further includes an operation 812. At operation 812, method 800
includes determining a first assignment of coverage enhancement
levels for each of the first device group and the second device
group using the NRSRP values. For example, as described above in
reference to FIG. 6, the NRSRP values for first device group 501
and second device group 502 are compared with first threshold value
604 (NRSRP1) and second threshold value 606 (NRSRP2) to determine
the assignment to one of Normal enhancement level 610, Robust
coverage enhancement level 620, or Extended coverage enhancement
level 630 for each device group.
[0078] After assignment of coverage enhancement levels at operation
812, method 800 proceeds to an operation 814, where a new physical
resource block is selected for communication in the WWAN by the
NB-IoT devices. Upon selection of the new physical resource block,
measurements of updated NRSRP values are obtained for each device
group at an operation 816. For example, as described in reference
to FIG. 7 above, upon selection of the new physical resource block
of the WWAN spectrum (e.g., WWAN 114 shown in FIG. 1) updated
measurements of NRSRP values for first device group 501 and second
device group 502 are obtained.
[0079] Based on these updated NRSRP values obtained at operation
816, method 800 proceeds to an operation 818 where a new assignment
(i.e., a second assignment) of coverage enhancement levels is
determined for the device groups. For example, as described in
reference to FIG. 7, the updated NRSRP values for first device
group 501 and second device group 502 are used to dynamically
change assignments of coverage enhancement levels.
[0080] After operation 818, method 800 may end. Alternatively,
method 800 may proceed back to operation 814 to select another new
physical resource block and proceed through operations 816 and 818.
For example, in the case where the first selection of a new
physical resource block at operation 814 results in a worse
coverage enhancement level assignment (i.e., changing an assignment
from Robust coverage enhancement level 620 to Extended coverage
enhancement level 630), a different physical resource block
selection may improve the results.
[0081] With this mechanism, coverage enhancement levels for groups
of NB-IoT devices may be optimized relative to the two NRSRP
thresholds for determining assignment of coverage enhancement
levels to change the coverage enhancement level distribution of
NB-IoT devices within a cell to the minimum required level. Method
800 may be performed to implement this mechanism in steps with a
feedback loop to test the results of the change against NB-IoT
performance aspects, such as repetitions, loss of communication,
etc.
[0082] Reference is now made to FIG. 8B, a diagram which shows
repetitions used by a NB-IoT device in the Narrowband Physical
Downlink Control Channel (NPDCCH), the Narrowband Physical Downlink
Shared Channel (NPDSCH) and Narrowband Physical Uplink Shared
Channel (NPUSCH). These repetition trend counts can be used to
detect NB-IoT devices, according to the techniques described above.
For example, as shown at 822, the number of repetitions of downlink
control information (DCI) is 2 on the NPDCCH. At 824, the number of
repetitions on the NPDSCH is 4, and at 826, the number of
repetitions of an ACK in the NPUSCH is 2.
[0083] Physical Resource Block Interference Optimization
[0084] Referring now to FIGS. 9-10, techniques for physical
resource block optimization of NB-IoT devices configured in an
in-band deployment mode in a wireless wide area network for
mitigating interference are provided. In a NB-IoT deployment, the
capacity of the NB-IoT carrier is shared by all devices and
capacity is scalable by adding additional NB-IoT carriers. As
described above, in an in-band deployment, the NB-IoT PRB is
located within the WWAN band (e.g., PRB 118 in WWAN 114, as shown
in FIG. 1).
[0085] Selection of a PRB for uplink, as well as downlink, can lead
to interference challenges, especially with regard to the NB-IoT
uplink causing loss of WWAN uplink throughput. According to the
techniques of the example embodiments described herein, avoiding or
mitigating interference within selected PRBs uplink and/or downlink
may be optimized by selection of PRB.
[0086] As shown in FIG. 9, techniques for physical resource block
selection for NB-IoT devices to optimize interference in a wireless
wide area network may be implemented in an environment 900
according to an example embodiment. In this embodiment, environment
900 includes a plurality of user devices, including one or more
wireless user devices (e.g., first wireless user device 101, second
wireless user device 102, and third wireless user device 103) and
one or more NB-IoT devices (e.g., first NB-IoT device 104, second
NB-IoT device 105, and third NB-IoT device 106), as detailed above
in reference to FIG. 1. Environment 900 also includes NB-IoT base
station 120 anchored to WWAN base station 110 and sharing radio
resources, such as RF transceivers 112, with WWAN base station 110,
as also detailed above with reference to FIG. 1. It should be
understood that environment 900 may include additional user
devices, including additional wireless user devices and/or NB-IoT
devices.
[0087] According to the techniques for physical resource block
optimization of NB-IoT devices described herein, a noise floor
measurement for each of a plurality of physical resource blocks
(PRBs) is used to determine a location of a NB-IoT PRB to mitigate
its noise and interference on the parent WWAN band. Such a
selection of PRB may be made based on NB-IoT device grouping, as
detailed above, and may be made according to a predetermined
threshold and/or in accordance with a predefined policy.
[0088] In this embodiment, WWAN 114 includes a plurality of PRBs,
including a first PRB 901, a second PRB 902, a third PRB 904, and a
fourth PRB 906. In the example embodiments, four PRBs are shown for
the purposes of explanation, however, it should be understood that
a WWAN spectrum may include a larger number of PRBs.
[0089] Each PRB may be associated with a noise floor measurement
for that PRB. For example, as shown in FIG. 9, first PRB 901 has a
first noise floor measurement 910, second PRB 902 has a second
noise floor measurement 912, third PRB 904 has a third noise floor
measurement 914, and fourth PRB 906 has a fourth noise floor
measurement 916.
[0090] In this embodiment, fourth noise floor measurement 916 is
lower than first noise floor measurement 910, second noise floor
measurement 912 is lower than both fourth noise floor measurement
916 and first noise floor measurement 910, and third noise floor
measurement 914 is lower than each of second noise floor
measurement 912, fourth noise floor measurement 916, and first
noise floor measurement 910. As will be further described with
reference to FIG. 10, these noise floor measurements for the
plurality of PRBs 901, 902, 904, 906 may be used to assign NB-IoT
devices and/or wireless user devices to different PRBs such that
interference is mitigated and optimized.
[0091] Referring now to FIG. 10, a flowchart of a method 1000 for
selection of a physical resource block in a wireless wide area
network for optimizing interference from NB-IoT devices is shown
according to an example embodiment. In some embodiments, method
1000 may be implemented by a NB-IoT base station (e.g., NB-IoT base
station 120).
[0092] In this embodiment, method 1000 may begin at an operation
1002. At operation 1002, a noise floor measurement for a plurality
of physical resource blocks used for communication in a WWAN are
obtained. For example, as shown in FIG. 9, NB-IoT base station 120
may obtain noise floor measurements 910, 912, 914, 916 for
plurality of physical resource blocks 901, 902, 904, 906 of WWAN
114. Next, at an operation 1004, method 1000 further includes
determining a first physical resource block of the plurality of
physical resource blocks having a first noise floor measurement
that is lower than a second noise floor measurement for a second
physical resource block of the plurality of physical resource
blocks. For example, referring to FIG. 9, third physical resource
block 904 has third noise floor measurement 914 that is lower than
first noise floor measurement 910 associated with first physical
resource block 901.
[0093] At an operation 1006, one or more of a plurality of NB-IoT
devices are assigned to the first physical resource block
determined at operation 1004. For example, plurality of NB-IoT
devices 104, 105, 106 shown in FIG. 9 may be assigned to third
physical resource block 904 of WWAN 114 at operation 1006. Next, at
an operation 1008, one or more of a plurality of wireless user
devices are assigned to the second physical resource block
determined at operation 1004. For example, plurality of wireless
user devices 101, 102, 103 shown in FIG. 9 may be assigned to first
physical resource block 901 of WWAN 114 at operation 1008.
[0094] Upon completion of operation 1008, method 1000 may end. In
other embodiments, method 1000 may be performed on the basis of one
or more groups of NB-IoT devices, which may be grouped based on
repetition rates, as described above. In these embodiments, device
groups may be assigned to different physical resource blocks based
on performance criteria. For example, a first device group of
NB-IoT devices may be assigned to second physical resource block
902 having second noise floor measurement 912 and a second device
group of NB-IoT devices may be assigned to a different physical
resource block having a lower noise floor measurement, for example,
third physical resource block 904 having third noise floor
measurement 914 that is lower than second noise floor measurement
912.
[0095] With this arrangement, method 1000 provides a technique for
distributing the location of the physical resource block used by
NB-IoT devices to spread the potential interference and mitigate
the effects on other wireless devices, such as wireless user
devices communicating on the WWAN. The techniques described herein
use noise floor measurements associated with physical resource
blocks to prioritize assignment between NB-IoT devices and the
wireless user devices (e.g., LTE devices). In the example
embodiments, the NB-IoT devices are assigned to a physical resource
block having a lower noise floor measurement, while traditional
wireless user devices are assigned to a physical resource block
having a higher noise floor measurement. In other embodiments, a
uniform location of the physical resource block per band may be
assigned to NB-IoT devices to isolate the interference from NB-IoT
devices on the other wireless user devices.
[0096] Relative Narrowband Tx Power Information Element for
Roaming
[0097] Referring now to FIGS. 11-13, techniques for leveraging
relative narrowband transmit power (RNTP) information elements to
provide for power optimization for a roaming NB-IoT device are
provided according to an example embodiment.
[0098] FIG. 11 is a diagram illustrating a roaming scenario 1100
for a NB-IoT device 1114 traveling between coverage areas of two
different NB-IoT base stations, according to an example embodiment.
In this embodiment, roaming scenario 1100 includes a first coverage
area 1110 associated with a first NB-IoT base station 1112 and a
second coverage area 1120 associated with a second NB-IoT base
station 1122. First NB-IoT base station 1112 and second NB-IoT base
station 1122 may be substantially similar to NB-IoT base station
120, described above. In this embodiment, roaming NB-IoT device
1114 is currently located within first coverage area 1110, which is
being provided by first NB-IoT base station 1112.
[0099] In accordance with the 3GPP release 13 specifications,
enhanced signaling for inter-eNB coordinated multi-point
transmission and reception (CoMP) enhancements provide for usage of
RNTP. An RNTP information element (IE) may be exchanged between
neighboring eNB base stations that includes an RNTP indicator which
provides information about the physical resource block power level
information to the neighbor eNB base station to enable interference
avoidance in the frequency domain.
[0100] According to the techniques of the example embodiments
provided herein, RNTP information elements may be leveraged to
provide power optimization for a roaming NB-IoT device. Referring
now to FIG. 12, a diagram illustrating roaming scenario 1100 for
roaming NB-IoT device 1114 traveling to a new NB-IoT base station
is shown according to an example embodiment. In this embodiment,
roaming NB-IoT device 1114 is traveling from first coverage area
1110 associated with first NB-IoT base station 1112 to second
coverage area 1120 associated with second NB-IoT base station 1122.
In accordance with the techniques provided herein, first NB-IoT
base station 1112 may transmit or provide an RNTP information
element 1200 to second NB-IoT base station 1122.
[0101] In an example embodiment, RNTP information element 1200
provides, on a per physical resource block basis, information about
whether the downlink transmission power is lower than a value
indicated by an RNTP threshold included in the RNTP information
element 1200. The receiving eNB base station (i.e., second NB-IoT
base station 1122) may use this information to set its scheduling
policy for power optimization. For example, second NB-IoT base
station 1122 may select a physical resource block used for
communication in the WWAN for communicating with roaming NB-IoT
device 1114 based on the RNTP information included in RNTP
information element 1200 transmitted from first NB-IoT base station
1112.
[0102] In some embodiments, an RNTP information element (e.g., RNTP
information element 1200) may be exchanged between eNB base
stations (e.g., first NB-IoT base station 1112 and second NB-IoT
base station 1122) over an X2 interface using an X2 application
protocol load information message. The receiving eNB base station
(i.e., second NB-IoT base station 1122) may consider the received
RNTP information value included in RNTP information element valid
until reception of a new RNTP information element (e.g., provided
in a new load information message) that includes an update from the
home eNB base station (i.e., first NB-IoT base station 1112).
[0103] In this embodiment, RNTP information element 1200 is used
when roaming NB-IoT device 1114 is roaming from one NB-IoT base
station to another (e.g., from first NB-IoT base station 1112 to
second NB-IoT base station 1122), which results in roaming NB-IoT
device 1114 having a different cell identifier value. For example,
roaming NB-IoT device 1114 may have a first cell identifier value
associated with first NB-IoT base station 1112 while roaming NB-IoT
device 1114 is within first coverage area 1110. Upon traveling to
second coverage area 1120, roaming NB-IoT device 1114 may be
assigned a second cell identifier value associated with second
NB-IoT base station 1122, where the second cell identifier value is
different than the first cell identifier value.
[0104] In an example embodiment, receiving eNB base station (i.e.,
second NB-IoT base station 1122) may use the RNTP information
included in RNTP information element 1200 immediately upon
reception to optimize the downlink power to roaming NB-IoT device
1114 on a per physical resource block basis. For example, second
NB-IoT base station 1122 may select a physical resource block used
for communication in the WWAN for communicating with roaming NB-IoT
device 1114 based on the RNTP information included in RNTP
information element 1200 from first NB-IoT base station 1112.
Additionally, second NB-IoT base station 1122 may use this selected
physical resource block to communicate with roaming NB-IoT device
1114 without polling roaming NB-IoT device 1114 to measure its
repetition rate.
[0105] FIG. 13 is a flowchart of a method 1300 for using a relative
narrowband transmit power (RNTP) information element to optimize
power for a roaming NB-IoT device, according to an example
embodiment. In some embodiments, method 1300 may be implemented by
a home NB-IoT base station (e.g., first NB-IoT base station 1112)
to transmit an RNTP information element to a receiving NB-IoT base
station (e.g., second NB-IoT base station 1122).
[0106] In this embodiment, method 1300 may begin at an operation
1302, where a first NB-IoT base station identifies at least one
roaming NB-IoT device. For example, first NB-IoT base station 1112
may identify roaming NB-IoT device 1114 in roaming scenario 1100,
as shown in FIG. 11, as leaving first coverage area 1110 and
entering second coverage area 1120.
[0107] Next, method 1300 includes an operation 1304, where the
first NB-IoT base station determines at least a transmit power
associated with a transmission by the at least one roaming NB-IoT
device identified at operation 1302. For example, first NB-IoT base
station 1112 may determine a transmit power associated with
transmissions made to and/or from roaming NB-IoT device 1114. In
some embodiments, operation 1304 may include determining other
information associated with the roaming NB-IoT device, including,
for example, identifier information.
[0108] Method 1300 may proceed to an operation 1306, where the
first NB-IoT base station transmits an RNTP information element to
a second NB-IoT base station. The RNTP information element
transmitted or provided by the first NB-IoT base to the second
NB-IoT base station includes at least information associated with
the transmit power for the at least one roaming NB-IoT device,
obtained or determined at operation 1304. For example, as shown in
FIG. 12, first NB-IoT base station 1112 may transmit or provide
RNTP information element 1200 associated with roaming NB-IoT device
1114 to second NB-IoT base station 1122.
[0109] Upon transmitting the RNTP information element from the
first NB-IoT base station, method 1300 includes an operation 1308.
At operation 1308, the receiving NB-IoT base station is configured
to use the RNTP information element provided from operation 1306 to
adjust a transmit power used to communicate with the at least one
roaming NB-IoT device. For example, second NB-IoT base station 1122
may use information associated with a transmit power included in
RNTP information element 1200 to adjust a transmit power used to
communicate with roaming NB-IoT device 1114. That is, upon
traveling from first coverage area 1110 to second coverage area
1120, the transmit power for roaming NB-IoT device 1114 may be
immediately adjusted by second NB-IoT base station 1122 based on
the information included in RNTP information element 1200. With
this configuration, second NB-IoT base station 1122 is configured
to use a selected physical resource block (i.e., based on
information in RNTP information element 1200) to communicate with
roaming NB-IoT device 1114 without polling roaming NB-IoT device
1114 to measure its repetition rate.
[0110] After operation 1308, method 1300 may end. Additionally, in
some embodiments, method 1300 may be implemented for a plurality of
roaming NB-IoT devices. In such embodiments, method 1300 may
include similar operations as described above for the plurality of
roaming NB-IoT devices, including sending a plurality of RNTP
information elements to the receiving NB-IoT base station (e.g.,
second NB-IoT base station 1122). In other embodiments, a plurality
of roaming NB-IoT devices may roam into coverage areas associated
with a plurality of different NB-IoT base stations. In these other
such embodiments, the home NB-IoT base station (e.g., first NB-IoT
base station 1112) may send RNTP information elements to each
receiving NB-IoT base station for the coverage areas where the
roaming NB-IoT devices are traveling.
[0111] The techniques for leveraging RNTP information elements to
provide for power optimization for a roaming NB-IoT device provided
herein results in mitigating asymmetric power setting problems
between a roamed NB-IoT device and a new eNB (e.g., NB-IoT base
station). Such asymmetric power setting problems can cause packet
drops over the air in the downlink direction when an eNB with a
higher transmit power is sending data packets to a roaming NB-IoT
device which has a lower power level. The example embodiments
described above also reduces the need to poll 2048 physical
resource block repetitions from the eNB to identify a suitable
physical resource block to allocate for the roaming NB-IoT
device.
[0112] The example embodiments provide several benefits for
SON-based radio resource management for NB-IoT in-band deployments.
For example, using the techniques described herein, a NB-IoT device
need not wait for another discontinuous reception (DRX) cycle. To
extend a UE's battery lifetime, an RRC connected UE may be
configured with a DRX cycle. A DRX cycle consists of an `On
Duration` during which the UE should monitor the PDCCH and a `DRX
period` during which a UE can skip reception of downlink channels
for battery saving purposes. The transition between the short DRX
cycle, the long DRX cycle and continuous reception is controlled
either by a timer or by explicit commands from the base
station.
[0113] Conventional physical resource block based scanning for
multiple iterations until 2048 repetitions can take a significant
amount of time, thereby contributing to an increase in airtime
utilization for scanning control and management packets. This
additional scanning latency is avoided with the techniques of the
example embodiments, which may be especially useful in roaming
scenarios.
[0114] Reference is now made to FIG. 14. FIG. 14 shows a power
consumption transition pattern 1400 during a NB-IoT device's
connection phase. P.sub.TX is the power consumption during a
transmission, P.sub.RX is a power consumption during a reception,
P.sub.I is power consumption with inactive and P.sub.S is power
consumption when in deep sleep. For a NB-IoT device, an extended
DRX cycle of 10.24 sec is supported in RRC connected state. In RRC
idle state, the maximum DRX cycle is 2.91 hours. For the Power
Saving Mode (PSM) state, the maximum PSM time is 310 hours. The
extension of both mechanisms implies a higher latency because the
network will wait a longer period of time until it is able to reach
the user device. However, this reduces power consumption of the
user device. According to the techniques presented herein, and as
shown at 1410, the RNTP IE is used for a roaming NB-IoT device and
as a result the NB-IoT device need not wait for an additional DRX
cycle to assign the correct power level in the downlink direction
to the NB-IoT device.
[0115] Additionally, the principles of the example embodiments
described herein can provide a roaming NB-IoT device with optimized
transmit power towards its direction of travel immediately after
entering a new coverage area. This can result in a better user
experience and mission critical payloads can be delivered to a
NB-IoT device earlier without undergoing any asymmetric power
setting problems resulting in packet drops over the air.
[0116] Techniques described herein for NB-IoT device grouping and
wireless user device grouping (e.g., LTE devices) based on radio
resource allocation provides efficient utilization of WWAN airtime
in both the uplink and downlink directions.
[0117] Furthermore, the techniques for NB-IoT device grouping and
wireless user device grouping also allow for flexibility in
applying radio policies from the same eNB, which may handle both
wireless user devices (e.g., LTE devices) and NB-IoT devices, to
handle the traffic more effectively. This radio policy can be
applied for different kinds of NB-IoT devices. For example, NB-IoT
sensors used in smart parking systems that may be deployed in
basements of buildings where radio coverage is poor need robust
NRSRP allocations, whereas NB-IoT devices deployed in a smart city
or enterprise environment will be sufficient with normal coverage
levels.
[0118] In summary, a method is provided comprising: providing a
narrowband Internet-of-Things (NB-IoT) base station in an in-band
deployment mode to operate within a wide area wireless network
(WWAN), wherein the NB-IoT base station is configured to use a
physical resource block of the WWAN for communicating with a
plurality of NB-IoT devices; causing, by the NB-IoT base station, a
reduction of a power level for a transmission using the physical
resource block from an initial power level to a first reduced power
level; obtaining, by the NB-IoT base station, parameters associated
with performance and throughput for the WWAN; comparing, by the
NB-IoT base station, the parameters to a quality threshold; and
based on the comparison of the parameters to the threshold,
determining, by the NB-IoT base station, whether or not to reduce
the power level for the physical resource block from the first
reduced power level to a second reduced power level.
[0119] In another form, a non-transitory computer readable storage
media encoded with instructions is provided that, when executed by
a processor of a narrowband Internet-of-Things (NB-IoT) base
station operating in an in-band deployment mode within a wide area
wireless network (WWAN), causes the processor to: reduce a power
level for a physical resource block of the WWAN used for
communicating with a plurality of NB-IoT devices from an initial
power level to a first reduced power level; obtain parameters
associated with performance and throughput for the WWAN; compare
the parameters to a quality threshold; and based on the comparison
of the parameters to the threshold, determine whether or not to
reduce the power level for the physical resource block from the
first reduced power level to a second reduced power level.
[0120] Furthermore, an apparatus is provided comprising: a
transceiver configured to transmit and receive signals in a
wireless wide area network (WWAN); a modem coupled to the
transceiver and configured to modulate signals and demodulate
signals; a processor coupled to the modem and to the transceiver,
wherein the processor is configured to: reduce a power level for a
physical resource block of the WWAN used for communicating with a
plurality of NB-IoT devices from an initial power level to a first
reduced power level; obtain parameters associated with performance
and throughput for the WWAN; compare the parameters to a quality
threshold; and based on the comparison of the parameters to the
threshold, determine whether or not to reduce the power level for
the physical resource block from the first reduced power level to a
second reduced power level.
[0121] In another embodiment, a method is provided comprising:
monitoring, by a narrowband Internet-of-Things (NB-IoT) base
station in an in-band deployment mode operating within a wide area
wireless network (WWAN), a repetition rate of transmissions made by
a plurality of NB-IoT devices; assigning one or more of the
plurality of NB-IoT devices associated with a first repetition rate
to a first device group; assigning one or more of the plurality of
NB-IoT devices associated with a second repetition rate to a second
device group, wherein the second repetition rate is different than
the first repetition rate; upon selection of an initial physical
resource block used for communication in the WWAN, obtaining
measurements of narrowband reference signal received power values
for the first device group and the second device group; based on
the narrowband reference signal received power values, determining
a first assignment of coverage enhancement levels for each of the
first device group and the second device group; selecting a new
physical resource block; obtaining measurements of updated
narrowband reference signal received power values for the first
device group and the second device group associated with the new
physical resource block; and based on the updated narrowband
reference signal received power values, determining a second
assignment of coverage enhancement levels for each of the first
device group and the second device group.
[0122] In some embodiments, determining the first assignment of
coverage enhancement levels includes assigning the first device
group to a first enhancement level and assigning the second device
group to a second enhancement level, wherein the second enhancement
level is different than the first enhancement level.
[0123] In some embodiments, determining the second assignment of
coverage enhancement levels includes assigning the first device
group to the first enhancement level and assigning the second
device group to the first enhancement level.
[0124] In some embodiments, the coverage enhancement levels
comprise: a normal enhancement level associated with a maximum
coupling loss of 144 dB, a robust enhancement level associated with
a maximum coupling loss of 154 dB, and an extended enhancement
level associated with a maximum coupling loss of 164 dB.
[0125] In some embodiments, each coverage enhancement level is
associated with a set of Narrowband Physical Random Access Channel
(NPRACH) resources for that coverage enhancement level.
[0126] In some embodiments, the set of NPRACH resources includes a
subset of subcarriers, a number of NPRACH repetitions, and a
maximum number of attempts a NB-IoT device may make.
[0127] In another embodiment, a non-transitory computer readable
storage media encoded with instructions is provided that, when
executed by a processor of a narrowband Internet-of-Things (NB-IoT)
base station operating in an in-band deployment mode within a wide
area wireless network (WWAN), causes the processor to: monitor a
repetition rate of transmissions made by a plurality of NB-IoT
devices; assign one or more of the plurality of NB-IoT devices
associated with a first repetition rate to a first device group;
assign one or more of the plurality of NB-IoT devices associated
with a second repetition rate to a second device group, wherein the
second repetition rate is different than the first repetition rate;
upon selection of an initial physical resource block used for
communication in the WWAN, obtain measurements of narrowband
reference signal received power values for the first device group
and the second device group; based on the narrowband reference
signal received power values, determine a first assignment of
coverage enhancement levels for each of the first device group and
the second device group; select a new physical resource block;
obtain measurements of updated narrowband reference signal received
power values for the first device group and the second device group
associated with the new physical resource block; and based on the
updated narrowband reference signal received power values,
determine a second assignment of coverage enhancement levels for
each of the first device group and the second device group.
[0128] Furthermore, in another embodiment, an apparatus is provided
comprising: a transceiver configured to transmit and receive
signals in a wireless wide area network (WWAN); a modem coupled to
the transceiver and configured to modulate signals and demodulate
signals; a processor coupled to the modem and to the transceiver,
wherein the processor is configured to: monitor a repetition rate
of transmissions made by a plurality of NB-IoT devices; assign one
or more of the plurality of NB-IoT devices associated with a first
repetition rate to a first device group; assign one or more of the
plurality of NB-IoT devices associated with a second repetition
rate to a second device group, wherein the second repetition rate
is different than the first repetition rate; upon selection of an
initial physical resource block used for communication in the WWAN,
obtain measurements of narrowband reference signal received power
values for the first device group and the second device group;
based on the narrowband reference signal received power values,
determine a first assignment of coverage enhancement levels for
each of the first device group and the second device group; select
a new physical resource block; obtain measurements of updated
narrowband reference signal received power values for the first
device group and the second device group associated with the new
physical resource block; and based on the updated narrowband
reference signal received power values, determine a second
assignment of coverage enhancement levels for each of the first
device group and the second device group.
[0129] In another embodiment, a method is provided comprising:
obtaining by a narrowband Internet-of-Things (NB-IoT) base station
in an in-band deployment mode operating within a wide area wireless
network (WWAN), a noise floor measurement for a plurality of
physical resource blocks used for communication in the WWAN;
determining a first physical resource block of the plurality of
physical resource blocks having a first noise floor measurement
that is lower than a second noise floor measurement for a second
physical resource block of the plurality of physical resource
blocks; assigning one or more of a plurality of NB-IoT devices to
the first physical resource block; and assigning one or more
wireless user devices to the second physical resource block.
[0130] In some embodiments, the method further comprises:
identifying, by the NB-IoT base station, the plurality of NB-IoT
devices based on at least a detected repetition rate on a physical
random access channel of a transmission made by a device of the
plurality of NB-IoT devices.
[0131] In some embodiments, identifying the plurality of NB-IoT
devices includes monitoring Signal-Information Blocks in the
transmission made by a device of the plurality of NB-IoT
devices.
[0132] In some embodiments, the method further comprises: grouping
one or more of the plurality of NB-IoT devices associated with a
first repetition rate to a first device group; grouping one or more
of the plurality of NB-IoT devices associated with a second
repetition rate to a second device group, wherein the second
repetition rate is different than the first repetition rate;
assigning at least one of the first device group or the second
device group to the first physical resource block.
[0133] In some embodiments, the first device group is assigned to
the first physical resource block, the method further comprises:
assigning the second device group to a third physical resource
block, wherein the third physical resource block has a third noise
floor measurement that is lower than the second noise floor
measurement for the second physical resource block.
[0134] In some embodiments, the first physical resource block and
the second physical resource block are selected based on minimizing
interference between the plurality of NB-IoT devices and the one or
more wireless user devices.
[0135] In another embodiment, a non-transitory computer readable
storage media encoded with instructions is provided that, when
executed by a processor of a narrowband Internet-of-Things (NB-IoT)
base station operating in an in-band deployment mode within a wide
area wireless network (WWAN), causes the processor to: obtain a
noise floor measurement for a plurality of physical resource blocks
used for communication in the WWAN; determine a first physical
resource block of the plurality of physical resource blocks having
a first noise floor measurement that is lower than a second noise
floor measurement for a second physical resource block of the
plurality of physical resource blocks; assign one or more of a
plurality of NB-IoT devices to the first physical resource block;
and assign one or more wireless user devices to the second physical
resource block.
[0136] Furthermore, in another embodiment, an apparatus is provided
comprising: a transceiver configured to transmit and receive
signals in a wireless wide area network (WWAN); a modem coupled to
the transceiver and configured to modulate signals and demodulate
signals; a processor coupled to the modem and to the transceiver,
wherein the processor is configured to: obtain a noise floor
measurement for a plurality of physical resource blocks used for
communication in the WWAN; determine a first physical resource
block of the plurality of physical resource blocks having a first
noise floor measurement that is lower than a second noise floor
measurement for a second physical resource block of the plurality
of physical resource blocks; assign one or more of a plurality of
NB-IoT devices to the first physical resource block; and assign one
or more wireless user devices to the second physical resource
block.
[0137] In another embodiment, a method is provided comprising:
identifying, by a first narrowband Internet-of-Things (NB-IoT) base
station in an in-band deployment mode operating within a wide area
wireless network (WWAN), at least one roaming NB-IoT device;
determining, by the first NB-IoT base station, at least a transmit
power associated with a transmission made by the at least one
roaming NB-IoT device; transmitting, by the first NB-IoT base
station, a relative narrowband transmit power (RNTP) information
element to a second NB-IoT base station, wherein the RNTP
information element includes at least information associated with
the transmit power for the at least one roaming NB-IoT device; and
wherein the second NB-IoT base station is configured to use the
RNTP information element from the first NB-IoT base station to
adjust a transmit power of the second NB-IoT base station used to
communicate with the at least one roaming NB-IoT device.
[0138] In some embodiments, the method further comprises: providing
the RNTP information element to the second NB-IoT base station via
an X2 interface using an X2 application protocol load information
message.
[0139] In some embodiments, the second NB-IoT base station is
configured to select a physical resource block used for
communication in the WWAN for communicating with the at least one
roaming NB-IoT device based on the RNTP information from the first
NB-IoT base station.
[0140] In some embodiments, the second NB-IoT base station is
configured to use the selected physical resource block to
communicate with the at least one roaming NB-IoT device without
polling the at least one roaming NB-IoT device to measure a
repetition rate of the at least one roaming NB-IoT device.
[0141] In some embodiments, the at least one roaming NB-IoT device
has a first cell identifier value associated with the first NB-IoT
base station; and wherein the at least one roaming NB-IoT device is
assigned a second cell identifier value associated with the second
NB-IoT base station, wherein the second cell identifier value is
different than the first cell identifier value.
[0142] In some embodiments, the method further comprises:
transmitting, by the first NB-IoT base station, a plurality of RNTP
information elements to the second NB-IoT base station for a
plurality of roaming NB-IoT devices
[0143] In another embodiment, a non-transitory computer readable
storage media encoded with instructions is provided that, when
executed by a processor of a first narrowband Internet-of-Things
(NB-IoT) base station operating in an in-band deployment mode
within a wide area wireless network (WWAN), causes the processor
to: identify at least one roaming NB-IoT device; determine at least
a transmit power associated with a transmission made by the at
least one roaming NB-IoT device; transmit a relative narrowband
transmit power (RNTP) information element to a second NB-IoT base
station, wherein the RNTP information element includes at least
information associated with the transmit power for the at least one
roaming NB-IoT device; and wherein the second NB-IoT base station
is configured to use the RNTP information element from the first
NB-IoT base station to adjust a transmit power of the second NB-IoT
base station used to communicate with the at least one roaming
NB-IoT device.
[0144] Furthermore, in another embodiment, an apparatus is provided
comprising: a transceiver configured to transmit and receive
signals in a wireless wide area network (WWAN); a modem coupled to
the transceiver and configured to modulate signals and demodulate
signals; a processor coupled to the modem and to the transceiver,
wherein the processor is configured to: identify at least one
roaming NB-IoT device; determine at least a transmit power
associated with a transmission made by the at least one roaming
NB-IoT device; transmit a relative narrowband transmit power (RNTP)
information element to a NB-IoT base station, wherein the RNTP
information element includes at least information associated with
the transmit power for the at least one roaming NB-IoT device; and
wherein the NB-IoT base station is configured to use the RNTP
information element from the apparatus to adjust a transmit power
of the NB-IoT base station used to communicate with the at least
one roaming NB-IoT device.
[0145] The above description is intended by way of example only.
Although the techniques are illustrated and described herein as
embodied in one or more specific examples, it is nevertheless not
intended to be limited to the details shown, since various
modifications and structural changes may be made within the scope
and range of equivalents of the claims.
* * * * *