U.S. patent application number 13/461263 was filed with the patent office on 2013-11-07 for determining speed dependent scaling factors.
The applicant listed for this patent is Tomasz Henryk Mach. Invention is credited to Tomasz Henryk Mach.
Application Number | 20130295951 13/461263 |
Document ID | / |
Family ID | 48428491 |
Filed Date | 2013-11-07 |
United States Patent
Application |
20130295951 |
Kind Code |
A1 |
Mach; Tomasz Henryk |
November 7, 2013 |
DETERMINING SPEED DEPENDENT SCALING FACTORS
Abstract
Apparatus and methods for self-optimizing speed dependent
scaling mechanisms are provided. A user equipment (UE) may
determine its mobility state by using the cell reselection
parameters included in a system information block message to
identify a conjectural average time between cell reselections,
calculating a current value of the average time between cell
reselections at the UE, and comparing both values to determine its
current mobility state. Different speed dependent scaling factors
may be selected for a determined mobility state of the UE, allowing
adapting the mobility parameters with a finer granularity. The
mobility parameters may be adjusted using the corresponding speed
dependent scaling factors, which in turn provide enhanced mobility
performance for the UE.
Inventors: |
Mach; Tomasz Henryk; (Fleet,
GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Mach; Tomasz Henryk |
Fleet |
|
GB |
|
|
Family ID: |
48428491 |
Appl. No.: |
13/461263 |
Filed: |
May 1, 2012 |
Current U.S.
Class: |
455/456.1 ;
455/517; 455/525 |
Current CPC
Class: |
H04W 48/20 20130101;
H04W 48/12 20130101; H04W 36/32 20130101 |
Class at
Publication: |
455/456.1 ;
455/517; 455/525 |
International
Class: |
H04W 36/32 20090101
H04W036/32; H04W 24/00 20090101 H04W024/00; H04W 8/02 20090101
H04W008/02 |
Claims
1. A method in a user equipment (UE), comprising: calculating a
conjectural average time between cell reselections based on
broadcasted parameters and a current value of an average time
between cell reselections; determining, by the UE, a speed
dependent scaling factor based on the conjectural average time
between cell reselections and the current value of the average time
between cell reselections; determining a mobility parameter based
on the speed dependent scaling factor and a broadcast parameter;
and executing a mobility procedure using the mobility
parameter.
2. The method of claim 1, wherein determining the mobility
parameter includes applying the speed dependent scaling factor to a
parameter received from a base station.
3. The method of claim 1, wherein the mobility procedure comprises
a cell reselection procedure.
4. The method of claim 1, wherein the speed dependent scaling
factor is associated with a cell reselection timer or a cell
reselection hysteresis parameter.
5. (canceled)
6. The method of claim 1, wherein the conjectural average time
between cell reselections is determined based on a period for
evaluating a number of cell reselections and a minimum number of
cell reselections in a medium mobility state.
7. The method of claim 6, further comprising receiving a system
information broadcast (SIB) message identifying the period for
evaluating the number of cell reselections and the minimum number
of cell reselections in the medium mobility state.
8. The method of claim 1, wherein the speed dependent scaling
factor is one of a plurality of different speed dependent scaling
factors associated with a mobility state.
9. The method of claim 8, wherein determining the speed dependent
scaling factor comprises selecting the speed dependent scaling
factor from the plurality of speed dependent scaling factors
associated with the mobility state.
10. The method of claim 1, further comprising determining a speed
of the UE using a global positioning system (GPS), wherein the
speed dependent scaling factor is based on the determined
speed.
11. The method of claim 1, wherein the mobility procedure comprises
a cell handover procedure.
12. The method of claim 11, wherein the speed dependent scaling
factor is associated with a time-to-trigger parameter or a
measurement report event trigger threshold.
13. A user equipment (UE) comprising one or more processors
configured to: calculate a conjectural average time between cell
reselections based on broadcasted parameters and a current value of
the average time between cell reselections; determine a speed
dependent scaling factor based on the conjectural average time
between cell reselections and the current value of an average time
between cell reselections; determine a mobility parameter based on
the speed dependent scaling factor and a broadcast parameter; and
execute a mobility procedure using the mobility parameter.
14. The user equipment of claim 13, wherein determining the
mobility parameter includes applying the speed dependent scaling
factor to a parameter received from a base station.
15. The user equipment of claim 13, wherein the mobility procedure
comprises a cell reselection procedure.
16. The user equipment of claim 13, wherein the speed dependent
scaling factor is associated with a cell reselection timer or a
cell reselection hysteresis parameter.
17. (canceled)
18. The user equipment of claim 13, wherein the conjectural average
time between cell reselections is determined based on a period for
evaluating a number of cell reselections and a minimum number of
cell reselections in a medium mobility state.
19. The user equipment of claim 18, the one or more processors
further configured to receive a system information broadcast (SIB)
message identifying the period for evaluating the number of cell
reselections and the minimum number of cell reselections in the
medium mobility state.
20. The user equipment of claim 13, wherein the speed dependent
scaling factor is one of a plurality of different speed dependent
scaling factors associated with a mobility state.
21. The user equipment of claim 20, wherein determining the speed
dependent scaling factor comprises selecting the speed dependent
scaling factor from the plurality of speed dependent scaling
factors associated with the mobility state.
22. The user equipment of claim 13, the one or more processors
further configured to determine a speed of the UE using a global
positioning system (GPS), wherein the speed dependent scaling
factor is based on the determined speed.
23. The user equipment of claim 13, wherein the mobility procedure
comprises a cell handover procedure.
24. The user equipment of claim 23, wherein the speed dependent
scaling factor is associated with a time-to-trigger parameter or a
measurement report event trigger threshold.
Description
FIELD
[0001] This disclosure relates to mobility procedures in wireless
communication networks and, more particularly, to determining speed
dependent scaling mechanism factors.
BACKGROUND
[0002] In cellular networks, user equipment (UE) may travel in a
large geographical area which often leads to the UE changing
serving cells. The UE may conduct mobility procedures such as cell
reselection or cell handover to connect with other base stations.
The mobility procedures may have different requirements depending
on speeds of the UEs physically travelling through geographical
areas. For example, a UE travelling at a high speed typically
requires a short latency to switch from one cell to another cell.
Otherwise, the signal quality with the current serving cell may
degrade fast and may result in the UE losing the existing
connection. In contrast, a UE travelling at a low speed can
tolerate a longer latency to switch between serving cells. For UEs
travelling at a low speed, the mobility procedures may include
stricter criteria to minimize or otherwise reduce switching back
and forth between serving cells, i.e., ping-pong events.
DESCRIPTION OF DRAWINGS
[0003] For a more complete understanding of this disclosure,
reference is now made to the following brief description, taken in
connection with the accompanying drawings and detailed description,
wherein like reference numerals represent like parts.
[0004] FIG. 1 is a schematic representation of a long term
evolution (LTE) wireless cellular communication system;
[0005] FIG. 2 is a schematic representation of a Universal Mobile
Telecommunications System (UMTS) wireless cellular communication
system;
[0006] FIG. 3 is a schematic block diagram illustrating an access
node device;
[0007] FIG. 4 is a schematic block diagram illustrating a user
equipment device;
[0008] FIG. 5 is a flow chart illustrating an example method for
self-optimizing mobility state dependent scaling mechanism in a
user equipment;
[0009] FIG. 6 is a schematic diagram illustrating an example method
for calculating current value of an average time between cell
reselections; and
[0010] FIG. 7 is a schematic diagram illustrating an example method
for determining speed dependent scaling factors.
DETAILED DESCRIPTION
[0011] The present disclosure is directed to systems and methods
for self-optimizing speed dependent scaling for mobility parameters
in user equipment (UE). In a cellular wireless network, a UE may
execute mobility procedures (e.g., cell reselection, cell handover)
to switch a connection from one base station to another base
station as the UE travels across cell boundaries. Depending on the
speed of the UE, the mobility parameters can be scaled up or scaled
down to optimize, maximize, or otherwise increase mobility
performance of the UE. In this disclosure, reference to a speed of
a UE refers to the speed that a UE moves through space. For
example, the mobility parameters such as cell reselection timer and
cell reselection hysteresis value may be adjusted based on
different UE speeds to increase a cell-reselection success ratio.
For another example, mobility parameters such as a time-to-trigger
timer and a measurement-report event trigger threshold may be
adjusted based on different UE speeds to improve a cell-handover
success rate.
[0012] To enhance the mobility performance, in some
implementations, the UE can determine a mobility state and scaling
factors for the mobility parameters by executing one or more of the
following: identify a conjectural average time between cell
reselections based on broadcasted messages from a base station such
as an evolved Node B (eNB); determine a current average time
between cell reselections for the UE; compare the conjectural
average time between cell reselections and the current average time
between cell reselections to determine the mobility state and
associated scaling factors; or others. In connection with one or
more of these processes, the UE may apply the scaling factors to
the mobility parameters and execute mobility procedures using the
scaled mobility parameters. In some implementations, the UE may
also determine a mobility state and associated scaling factors
using a global positioning system (GPS). In either case, the UE may
select an appropriate scaling factor for the mobility parameters to
improve the performance of the mobility procedures. In some
implementations, the granularity of the scaling factors can be
increased, and as a result, the values of the mobility parameters
can be further fine-tuned. For example, for each mobility state,
multiple scaling factors may be associated with one mobility
parameter. Additionally, since the UE autonomously determines and
adjusts the mobility parameters, the network would need little
effort and cost to implement the UE-determined scaling factors.
[0013] FIG. 1 is a schematic representation of a long term
evolution (LTE) wireless cellular communication system, also known
as Evolved Universal Terrestrial Radio Access Network (E-UTRAN).
The cellular network system 100 shown in FIG. 1 includes a
plurality of base stations 112a and 112b. In the LTE example of
FIG. 1, the base stations are shown as evolved NodeBs (eNBs) 112a
and 112b. The base stations 112a and 112b may operate in any mobile
environment including macro cell, femto cell, pico cell, or the
base station may operate as a node that can relay signals for other
mobile and/or base stations. The example LTE system 100 may include
one or more radio access networks 110, core networks (CNs) 120, and
external networks 130. In certain implementations, the radio access
networks 110 may be E-UTRANs. In addition, the core networks 120
may be evolved packet cores (EPCs). Further, the system 100 may
include one or more mobile electronic devices 102a and 102b. In
some implementations, the system 100 may include 2G/3G systems 140
such as Global System for Mobile communication (GSM), Interim
Standard 95 (IS-95), Universal Mobile Telecommunications System
(UMTS), CDMA2000 (Code Division Multiple Access), or others.
[0014] In the example LTE system 100, the EUTRAN 110 includes eNB
112a and eNB 112b. As illustrated, the eNB 112a includes a service
area, i.e., cell 114a and the eNB 112b includes a service area
indicated as cell 114b. The eNB 112a serves UEs 102a and 102b which
operate in cell 114a. Similarly or in contrast to the illustrated
system 100, the EUTRAN 110 can include one or more eNBs (e.g., eNB
112a, eNB 112b) and one or more UEs (e.g., UE 102a and UE 102b)
without departing from the scope of the disclosure. In this
example, the eNBs 112a and 112b communicate directly with the UEs
102a and 102b. In some implementations, the eNB 112a or 112b may be
in a one-to-many relationship with the UEs 102a and 102b. For
example, the eNB 112a may serve multiple UEs, such as bot UE 102a
and UE 102b, within the cell 114a, but each of UE 102a and UE 102b
may be connected only to one eNB 112a at a time. In some
implementations, the eNBs 112a and 112b can be in a many-to-many
relationship with the UEs. For example, UE 102a and UE 102b may be
connected to both eNB 112a and eNB 112b. The eNB 112a may be
connected to eNB 112b with which mobility procedures (e.g., cell
handover, cell reselection) may be executed for one or both of the
UE 102a and UE 102b when switching between cell 114a and cell 114b.
The eNBs 112a or 112b may determine mobility parameters (e.g.,
time-to-trigger, measurement report event trigger threshold, cell
reselection timer, cell reselection hysteresis parameter) for the
UE 102a or 102b which are used to execute mobility procedures. To
increase success rates of mobility procedures, the mobility
parameters may be scaled up or scaled down depending on the speed
of UE 102a or 102b. In some implementations, the UE 102a or 102b
may identify a speed or mobility state and determine appropriate
scaling factors for the mobility parameters. As such, the UE may
maximize, enhance or otherwise increase the mobility performance
using the self-scaled mobility parameters. Moreover, the system 100
may need little or no cost and effort to implement the self-scaled
mobility parameters.
[0015] The UEs 102a and 102b may be any wireless electronic device
used by an end user to communicate, for example, within the LTE
system 100. The UE 102a or 102b may be referred to as mobile
electronic device, user device, mobile station, subscriber station,
or wireless terminal. The UE 102a or 102b may be a cellular phone,
personal data assistant (PDA), smart phone, laptop, tablet personal
computer (PC), pager, portable computer, or other wireless
communications device.
[0016] The UEs 102a and 102b may transmit voice, video, multimedia,
text, web content and/or any other user/client-specific content. On
the one hand, the transmission of some of these contents, e.g.,
video and web content, may include high channel throughput to
satisfy the end user demand. On the other hand, the channel between
UEs 102a, 102b and eNBs 112 may be contaminated by multipath
fading, due to the multiple signal paths arising from many
reflections in the wireless environment. Accordingly, the UEs'
transmission may adapt to the wireless environment. In short, the
UEs 102a and 102b generate requests, send responses, or otherwise
communicate in different means with Enhanced Packet Core (EPC) 120
and/or Internet Protocol (IP) networks 130 through one or more eNBs
112.
[0017] The UEs 102a and 102b may switch from the coverage of one
cell to another cell, for example, from the coverage of the cell
114a to the coverage of the cell 114b. A mobility procedure (e.g.,
cell handover, cell reselection) may be executed to maintain a
connection between the UE 102a or 102b and the EUTRAN 110 when
switching between cells. As previously mentioned, different
mobility parameters may be used based on the speed of the UE. For
high-speed UEs, a smaller time-to-trigger value or cell reselection
timer may be used compared to low-speed UEs. For example, a
high-speed UE may include a UE moving at speeds in a range
including 30 km/h or more. High-speed UEs may move out of the cell
coverage quickly and thus need to switch to another cell quickly to
maintain a communication session. Also for high-speed UEs, a lower
value of the cell reselection hysteresis parameter or measurement
report trigger threshold may be used compared to low-speed UEs. For
example, a low-speed UE may include a UE moving at speeds in a
range including 0-5 km/h].
[0018] In general, mobile telecommunication systems include radio
access network such as UMTS, CDMA2000 and 3GPP LTE. As illustrated,
the LTE telecommunications system 100 includes a Radio Access
Network (RAN) referred to as EUTRAN 110. The EUTRAN 110 may be
located between UEs 102a, 102b and EPC 120. The EUTRAN 110 includes
at least one eNB 112. The eNB 112 can be a radio base station that
may control all or at least some radio related functions in a fixed
part of the system 100. The at least one eNB 112 can provide a
radio interface within the associated coverage area or cell 114 for
UE 102a and 102b. The eNBs 112 may be distributed throughout the
cellular network to provide a wide area of coverage. In short, the
eNB 112 directly communicates with at least one of UE 102a, UE
102b, other eNBs 112, or the EPC 120.
[0019] The eNB 112 may be the end point for radio protocols towards
the UEs 102a, 102b and may relay signals between the radio
connection and the connectivity towards the EPC 120. In certain
implementations, the EPC 120 is the main component of a core
network (CN). For example, the CN can be a backbone network which
may be a central part of the telecommunications system. The EPC 120
can include a mobility management entity (MME), a serving gateway
(SGW), and a packet data network gateway (PGW). The MME may be the
main control element in the EPC 120 responsible for the
functionalities comprising the control plane functions related to
subscriber and session management. The SGW can serve as a local
mobility anchor, such that the packets are routed through this
point for intra EUTRAN 110 mobility and mobility with other legacy
2G/3G systems 140. The SGW functions may include the user plane
tunnel management and switching. The PGW may provide connectivity
to the services domain comprising external networks 130, such as
the IP networks. The UE 102, EUTRAN 110, and EPC 120 may be
referred to as the evolved packet system (EPS).
[0020] While the following disclosure is described with respect to
the LTE system 100 of FIG. 1, the present disclosure is not limited
to this environment. In general, cellular telecommunication systems
may be described as cellular networks made up of a number of radio
cells or cells that are each served by a base station or other
fixed transceiver. The cells are used to provide radio coverage
over different areas. Example cellular telecommunication systems
include Global System for Mobile Communication (GSM) protocols,
Universal Mobile Telecommunications System (UMTS), 3GPP Long Term
Evolution (LTE), and others. In addition to cellular
telecommunication systems, wireless broadband communication systems
may also be suitable for the various implementations described in
the present disclosure. Example wireless broadband communication
systems include IEEE 802.11 wireless local area network, IEEE
802.16 WiMAX network, or others.
[0021] FIG. 2 is an example system 200 of a Universal Mobile
Telecommunications System (UMTS) wireless cellular communication
system. The system 200 includes a UMTS-based radio access network
(RAN), which is referred to as a UTRAN, and a third generation
partnership project (3GPP) general packet radio service (GPRS)
packet-switched core network. The core network provides
connectivity to an external network such as the Internet 240. The
system 200 includes one or more base stations such as Node-B base
stations 210a and 210b that provide wireless service(s) to one or
more devices such as UEs 205. A radio network controller (RNC) 215
can control the Node-B base stations 210a and 210b. The RNC 215 and
the Node-B base stations 210a and 210b form a RAN. The system 200
can include system elements 220, 225, 230, 235 that perform one or
more communication functions such as connection establishment and
data routing. For example, the system 200 includes a Serving GPRS
Support Node (SGSN) 220 that is responsible for routing traffic
within a core network. The system 200 includes a Gateway GPRS
Support Node (GGSN) 235 that is responsible for enabling the
ingress/egress of traffic from/to the Internet 240. The GGS 235 can
allocate IP addresses to UEs 205.
[0022] The network interfaces, for a UMTS-based system, include the
Uu interface defined between a UE and a Node-B, the Iub interface
defined between a Node-B and a RNC, the Iu interface defined
between a RNC and a SGSN, the Gn interface defined between a SGSN
and a GGSN, the Gi interface defined between a GGSN and an external
packet data network. User-plane connectivity through the radio
access network and core network can include establishing network
interfaces between the UE and Node-B (e.g., Uu interface), Node-B
and RNC (e.g., Iub interface), RNC and SGSN (e.g., Iu interface),
SGSN and GGSN (e.g., Gn interface), and GGSN and the Internet
(e.g., Gi interface). The establishment of one or more of these
network interfaces can be associated with a radio connection state
or sub-state as a function of the current activity level. For
example, the Uu, Iub and Iu connections may be established for
active user-plane data communication.
[0023] Similar to the LTE-based system, the UMTS-based system 200
enables the UEs 205 to switch from one base station to another base
station as the UEs 205 move across cell boundaries. The base
stations 210a and 210b may transmit mobility parameters such as
cell reselection timer and cell reselection hysteresis parameter to
the UEs 205. The cell reselection timer determines a time period
that the UE needs to wait before executing a cell reselection
procedure when a neighbor cell becomes higher ranked than the
current serving cell. The cell reselection hysteresis parameter
(e.g., 0-24 dB) is added to the measured serving cell power when
comparing the measured serving cell power to the neighboring cell
power during the cell ranking process. In these instances, the UE
may initiate the cell reselection only when the measured
neighboring cell power is higher than the serving cell power by at
least the value of the cell reselection hysteresis parameter. The
UEs 205 may execute the mobility procedures using the provided
mobility parameters. In some implementations, the UEs 205 may scale
the mobility parameters according to the UE speed or mobility state
to increase the success rate of mobility procedures. For example,
the UEs 205 may scale down the cell reselection timer when the UEs
205 are identified as being in a high mobility state. The UEs in
the high mobility state may also scale down the cell reselection
hysteresis parameter, which is the hysteresis value for cell
reselection ranking criteria. The UEs 205 may determine their
mobility states by utilizing broadcasted cell reselection
parameters. Alternatively or in addition, the UEs 205 may determine
their mobility state using a location system such as GPS.
[0024] FIG. 3 is a schematic block diagram 300 illustrating an
access node device. The illustrated device 300 includes a
processing module 302, a wired communication subsystem 304, and a
wireless communication subsystem 306. The processing module 302 can
include one or more processing components (alternatively referred
to as "processors" or "central processing units (CPUs)") capable of
executing instructions related to one or more of the processes,
steps, or actions described above in connection with one or more of
the implementations disclosed herein. The processing module 302 can
also include other auxiliary components, such as random access
memory (RAM), read only memory (ROM), secondary storage (for
example, a hard disk drive or flash memory), or others. In some
implementations, the processing module 302 may be configured to
mobility parameters for the UE. The mobility parameters may include
cell reselection parameters and cell handover parameters. The
access node device 300 may broadcast the cell reselection
parameters (e.g., cell reselection timer Treselection, cell
reselection hysteresis parameter Qhyst, duration for evaluating a
number of cell reselections T.sub.CRmax, minimum number of cell
reselections for a medium mobility state N.sub.CR.sub.--.sub.M)
using a System Information Block Type 3 (SIB3) message. The
processing module 302 may also be configured to determine speed
dependent scaling factors associated with the mobility parameters.
The processing module 302 can execute certain instructions and
commands to provide wireless or wired communication, using the
wired communication subsystem 304 or a wireless communication
subsystem 306. A skilled artisan may readily appreciate that other
components may also be included in the device 300 without departing
from the scope of the disclosure.
[0025] FIG. 4 is a schematic block diagram 400 illustrating a user
equipment device. The illustrated device 400 includes a processing
unit 402, a computer readable storage medium 404 (for example, ROM
or flash memory), a wireless communication subsystem 406, a user
interface 408, and an I/O interface 410.
[0026] Similar to the processing module 302 of FIG. 3, the
processing unit 402 can include one or more processing components
(alternatively referred to as "processors" or "central processing
units (CPUs)") configured to execute instructions related to one or
more of the processes, steps, or actions described above in
connection with one or more of the implementations disclosed
herein. In some implementations, the processing unit 402 may be
configured to determine speed dependent scaling factors associated
with the mobility parameters. Subsequently, the processing unit 402
may apply the speed dependent scaling factors to the associated
mobility parameters and execute mobility procedures (e.g., cell
reselection, cell handover) using the scaled mobility parameters.
The processing unit 402 may also include other auxiliary
components, such as random access memory (RAM) and read only memory
(ROM). The computer readable storage medium 404 can store an
operating system (OS) of the device 400 and various other computer
executable software programs for performing one or more of the
processes, steps, or actions described above.
[0027] The wireless communication subsystem 406 is configured to
provide wireless communication for data and/or control information
provided by the processing unit 402. The wireless communication
subsystem 406 can include, for example, one or more antennas, a
receiver, a transmitter, a local oscillator, a mixer, and/or a
digital signal processing (DSP) unit. In some implementations, the
subsystem 406 can support multiple input multiple output (MIMO)
transmissions.
[0028] The user interface 408 can include, for example, one or more
of a screen or touch screen (for example, a liquid crystal display
(LCD), a light emitting display (LED), an organic light emitting
display (OLED), a microelectromechanical system (MEMS) display), a
keyboard or keypad, a trackball, a speaker, and/or a microphone.
The I/O interface 410 can include, for example, a universal serial
bus (USB) interface. A skilled artisan may readily appreciate that
various other components can also be included in the device
400.
[0029] FIG. 5 is a flow chart 500 illustrating an example method
for self-optimizing, by a UE, mobility state dependent scaling
factors. As shown in FIG. 5, the UE camps on an initial cell at
step 502. The initial cell may have the strongest received signal
strength when the UE is switched on. The initial cell may be
referred to as a serving cell. At step 504, the UE may receive
broadcast system information from the serving cell. For example,
the serving cell may broadcast System Information Block (SIB)
messages including or otherwise identifying the system information.
The system information may include at least one of serving cell
radio resource configuration information, cell reselection
information, mobility parameters, neighboring cell information, or
others. After receiving the system information, the UE may
determine whether the network transmitted speed dependent scaling
factors for mobility parameters at step 506. For example, the UE
may determine whether the speed dependent scaling factors for cell
reselection parameters (e.g., Qhyst, Treselection) are contained in
the SIB3 message received from the serving cell. The UE may also
determine whether the network has transmitted the speed dependent
scaling factors for cell handover parameters (e.g., time-to-trigger
and measurement report event trigger threshold). The
time-to-trigger parameter determines a time period that the UE has
to wait before sending a measurement report to the base station
when a neighboring cell is detected with better signal quality or
strength. The measurement report event trigger threshold determines
a margin by which the signal quality or strength of the neighboring
cell has to be higher than the serving cell to initiate
transmission of a measurement report. For example, the UE may
determine whether the speed dependent scaling factors for cell
handover parameters are identified by Radio Resource Configuration
(RRC) messages received from the serving cell.
[0030] If the scaling factors for the mobility parameters are
provided by the network, the UE may apply the provided scaling
factors to the mobility parameters based on the UE mobility state
at step 508. In some implementations, the base station may indicate
to the UE whether the UE may overwrite the provided speed dependent
mobility parameters. If the scaling factors are not provided by the
network, the UE may determine the scaling factors. The UE may first
identify a conjectural average time between cell reselections
Tbetween_reselections_avg_m at step 510. The conjectural average
time between cell reselections, i.e., Tbetween_reselections_avg_m,
may be calculated based on the broadcasted parameters T.sub.CRmax,
i.e., a duration for evaluating a number of cell reselections, and
N.sub.CR.sub.--.sub.M, i.e., a minimum number of cell reselections
for a medium mobility state. In some implementations, the
conjectural average time between cell reselections may be
calculated by T.sub.CRmax/N.sub.CR.sub.--.sub.M, which is a ratio
of T.sub.CRmax to N.sub.CR.sub.--.sub.M. The base station may
transmit, to the UE, the broadcasted parameters in a SIB3
message.
[0031] The UE may then calculate the current value of the average
time between cell reselections at step 512. The current value of
the average time between cell reselections, i.e.,
Tbetween_reselection_avg, may depend on the speed of the UE. For
example, a high-speed UE may have a smaller average time between
cell reselections, i.e., Tbetween_reselection_avg, than a low-speed
UE. In particular, the history of UE cell reselections may be used
to calculate the current value of the average time between cell
reselections. In some implementation, the total time duration for
the last N.sub.CR.sub.--.sub.M cell reselections divided by
N.sub.CR.sub.--hd M may be the current value of the average time
between cell reselections, i.e., Tbetween_reselection_avg.
[0032] At step 514, the UE may then determine the mobility state
and the speed dependent scaling factors based on
Tbetween_reselections_avg_m, i.e., the conjectural average time
between cell reselections, and Tbetween_reselection_avg, i.e., the
current value of the average time between cell reselections. For
example, the UE may determine a low mobility state when
Tbetween_reselection avg is greater than
Tbetween_reselections_avg_m. In some instances, the UE may
determine a high mobility state when Tbetween_reselection_avg is
much smaller than Tbetween_reselections_avg_m and, thus, scale down
the related mobility parameters (e.g., cell reselection timer, cell
reselection hysteresis parameter, time-to-trigger, measurement
report event trigger threshold). An example of determining the
speed dependent scaling factors is described in connection with
FIG. 7.
[0033] Subsequently, the UE may apply the determined speed
dependent scaling factors to the mobility parameters at step 516.
Therefore, the mobility parameters may be adjusted based on the UE
speed. The UE may execute mobility procedures, such as cell
reselection and cell handover, using the adjusted mobility
parameters to increase the success rate of the mobility procedures.
As the speed of the UE changes, the UE may update the mobility
state and the speed dependent scaling factors and re-adjust the
mobility parameters correspondingly. In some implementations, the
UE may periodically update the current value of the average time
between cell reselections based on the recent history of the UE
cell reselections and re-determine the mobility state and speed
dependent scaling factors.
[0034] FIG. 6 is a schematic diagram 600 illustrating an example
method for calculating a current value of an average time between
cell reselections. As shown in FIG. 6, the UE 602 travels through
cell A 604, cell B 606, cell C 608, and cell D 610 during a certain
period of time. In this example, the cell reselection from cell A
604 to cell B 606 is referred to as the 1.sup.st cell reselection,
the cell reselection from cell B 606 to cell C 608 is referred to
as the 2.sup.nd cell reselection, and the cell reselection from
cell C 608 to cell D 610 is referred to as the 3.sup.rd cell
reselection. The UE may measure the time duration that the UE
camped on the previous cell each time a cell reselection occurs.
For example, the time duration 612 that the UE camped on cell B
before moving to cell C, i.e., the time duration between the
1.sup.st cell reselection and 2.sup.nd cell reselection (i.e.,
Tbetween_reselection12), may be measured, and the UE 602 may
calculate the current value of the average time between cell
reselections (i.e., Tbetween_reselection_avg) using
Tbetween_reselection12. Similarly, the time duration 614 between
the 2.sup.nd cell reselection and 3.sup.rd cell reselection (i.e.,
Tbetween_reselection23) may be measured and used to calculate the
current value of the average time between cell reselections. The
time duration between different cell reselections may vary because
cell sizes may be different and the UE speed may vary. For example,
time duration 612 is longer than time duration 614, as shown in
FIG. 6. The UE 602 may store a number of most recent cell
reselection times, discard out-dated cell reselection times, and
use part or all of the stored cell reselection times to calculate
the current value of the average time between cell reselections
(i.e., Tbetween_reselection_avg). In the illustrated example, the
UE calculates the current value of the average time between cell
reselections 616 based on cell reselection times 612 and 614.
Specifically, the current value of the average time between cell
reselections 616 may be calculated by the total of the cell
reselection times 612 and 614 divided by the number of cell
reselections (which is 2 in this case). In some implementations,
ping-pong reselections, i.e., continuous back and forth reselection
between two cells, may be excluded from the calculations of cell
reselection time.
[0035] Although the current value of the average time between cell
reselections is calculated in FIG. 6, in some implementations, the
current value of the average time between cell handovers may be
calculated instead to determine the UE mobility state and the speed
dependent scaling factors. For example, the UE may determine the
mobility state and the speed dependent scaling factors at step 514
(shown in FIG. 5) based on Tbetween_reselections_avg_m, i.e., the
conjectural average time between cell reselections, and
Tbetween_handover_avg, i.e., the current value of the average time
between cell handovers. The UE may determine a low mobility state
when Tbetween_handover_avg is greater than
Tbetween_reselections_avg_m. On the other hand, the UE may
determine a high mobility state when Tbetween_handover_avg is much
smaller than Tbetween_reselections_avg_m and, thus, scale down the
related mobility parameters accordingly. The current value of the
average time between cell handovers may be calculated based on time
durations between cell handovers, similar to the example method
shown in FIG. 6. In particular, the UE may measure a time duration
that the UE stays at the previous cell each time when a cell
handover occurs, and the UE may calculate the current value of the
average time between cell handover, i.e., Tbetween_handover_avg,
using a subset or all of the stored cell handover times. In some
implementations, when the UE is in a RRC connected mode with a base
station, the UE may calculate the current value of the average time
between cell handovers and determine the UE mobility state and the
speed dependent scaling factors based on the current value. When
the UE is in an idle mode and is not actively connected with the
base station, the UE may calculate the current value of the average
time between cell reselections and determine the UE mobility state
and the speed dependent scaling factors based on the current
value.
[0036] FIG. 7 is a schematic diagram 700 illustrating an example
method for determining speed dependent scaling factors for
different time periods. As shown in FIG. 7, different UE mobility
states and speed dependent scaling factors may be determined based
on the conjectural average time between cell reselections, i.e.,
Tbetween_reselections_avg_m, and the current value of the average
time between cell reselections, i.e., Tbetween_reselection_avg.
During period 702, the UE may determine a low mobility state when
Tbetween_reselection_avg is greater than
Tbetween_reselections_avg_m. Correspondingly, the speed dependent
scaling factor for Treselection, i.e., cell reselection timer, may
be 1.0, as shown at period 704, which means that no scaling would
be applied to the value of Treselection. Alternatively, the UE may
be in a medium mobility state at period 706 when
Tbetween_reselection_avg is greater than
0.5.times.Tbetween_reselections_avg_m and less than
Tbetween_reselections_avg_m. The speed dependent scaling factor for
Treselection may be determined to be 1.0 when
Tbetween_reselection_avg is greater than
0.75.times.Tbetween_reselections_avg_m, as shown at period 708. The
speed dependent scaling factor for Treselection may be 0.75 when
Tbetween_reselection_avg is less than
0.75.times.Tbetween_reselections_avg_m, as shown at period 710.
Therefore, different speed dependent scaling factors may be
selected for the medium mobility state based on the current value
of the average time between cell reselections. In other words, this
process may increase the granularity of the speed dependent scaling
factors resulting in a higher resolution. Similarly, the UE may
determine a high mobility state at period 712 when
Tbetween_reselection_avg is less than
0.5.times.Tbetween_reselections_avg_m. The speed dependent scaling
factor for Treselection may be 0.5 when Tbetween_reselection_avg is
greater than 0.25.times.Tbetween_reselections_avg_m, as shown at
period 714. The speed dependent scaling factor for Treselection may
be 0.25 when Tbetween_reselection_avg is less than
0.25.times.Tbetween_reselections_avg_m, as shown at 716.
[0037] FIG. 7 is a diagram 700 illustrating an example method for
determining the speed dependent scaling factors. Other scaling
factors may be used in connection with each mobility state. Higher
or lower resolutions for the scaling factors may be used for each
mobility state as well. For example, the medium mobility state may
include three different scaling factors 0.65, 0.8, and 1, and one
of these values may be selected based on the current value of the
average time between cell reselections. Further, for different
mobility parameters, different scaling factors or operations may be
used for each mobility state. As an example, for cell reselection
hysteresis parameter (i.e., Qhyst), an additive scaling operation
may be used instead of the multiplicative scaling operation. For
instance, a scaling factor of -2 dB or 0 dB may be selected for the
medium mobility state based on the current value of the average
time between cell reselections. For the high mobility state, a
scaling factor of -5 dB or -3 dB may be selected. Other values of
the scaling factors may be configured and selected by the UE as
well for each mobility state. Multiple mobility parameters may be
scaled using different scaling factors for each mobility state. In
some implementations, the time-to-trigger value used in the cell
handover procedures may be scaled using a similar method as the
method for scaling the cell reselection timer shown in FIG. 7.
Additionally, the measurement report event trigger threshold used
in the cell handover procedures may be scaled using an additive
scaling operation similar to the method for scaling the cell
hysteresis parameter.
[0038] Although the current value of the average time between cell
reselections is used to determine the UE mobility state and the
speed dependent scaling factors, as shown in FIG. 7, the current
value of the average time between cell handovers may be used to
determine the UE mobility state and the speed dependent scaling
factors. For example, the UE may have a low mobility state when
Tbetween_handover_avg, i.e., the current value of the average time
between cell handovers, is greater than
Tbetween_reselections_avg_m. Correspondingly, the speed dependent
scaling factor for Treselection, i.e., cell reselection timer, may
be determined to be 1.0, which means that no scaling would be
applied to the value of Treselection. Alternatively, the UE may be
at a medium mobility state when Tbetween_handover_avg is greater
than 0.5.times.Tbetween_reselections_avg_m and less than
Tbetween_reselections_avg_m. The speed dependent scaling factor for
Treselection may be 1.0 when Tbetween_handover_avg is greater than
0.75.times.Tbetween_reselections_avg_m. The speed dependent scaling
factor for Treselection may be 0.75 when Tbetween_handover_avg is
less than 0.75.times.Tbetween_reselections_avg_m. Similarly, the UE
may be at a high mobility state when Tbetween_handover_avg is less
than 0.5.times.Tbetween_reselections_avg_m. The speed dependent
scaling factor for Treselection may be 0.5 when
Tbetween_handover_avg is greater than
0.25.times.Tbetween_reselections_avg_m. The speed dependent scaling
factor for Treselection may be 0.25 when Tbetween_handover_avg is
less than 0.25.times.Tbetween_reselections_avg_m.
[0039] In some implementations, the UE may use GPS to determine the
speed of the UE and then directly determine the speed dependent
scaling factors based on the UE speed. For example, when the UE
speed is within a range of 0-30 kilometer (km) per hour, the
scaling factor for Treselection may be set to 1.0. The scaling
factor for Treselection may be set to 0.75 when the UE speed is
within a range of 30-60 km per hour. The scaling factor for
Treselection may be set to 0.5 when the UE speed is within a range
of 60-130 km per hour. The scaling factor for Treselection may be
set to 0.25 when the UE speed is higher than 130 km per hour.
Different speed dependent scaling factors may be used based on the
determined speed of the UEs. The number of possible scaling factors
is not limited by this disclosure and may be determined, e.g., by a
mobile phone manufacturer. Further, the UE may use other
positioning techniques to determine the speed of the UE and then
determine the speed dependent scaling factors based on the UE
speed.
[0040] In some implementations, when the speed dependent scaling
factors are provided by the network, the UE may compare them with
the values provided by the self-optimizing speed dependent scaling
method and determine which to apply. As shown in FIG. 7, the
self-optimizing speed dependent scaling method enables the UE to
automatically determine the mobility state and speed dependent
scaling factors. The UE may determine the resolution of the
mobility state and the speed dependent scaling factors based on the
mobility performance requirements and the UE processing power. This
method simplifies the mobility configuration of the wireless
communication system, reduces network configuration, maintenance
and management cost for a mobile operator, and improves the UE
mobility performance.
[0041] While several implementations have been provided in the
present disclosure, it should be understood that the disclosed
systems and methods may be embodied in many other specific forms
without departing from the scope of the present disclosure. The
present examples are to be considered as illustrative and not
restrictive, and the intention is not to be limited to the details
given herein. For example, the various elements or components may
be combined or integrated in another system or certain features may
be omitted, or not implemented.
[0042] Also, techniques, systems, subsystems and methods described
and illustrated in the various implementations as discrete or
separate may be combined or integrated with other systems, modules,
techniques, or methods without departing from the scope of the
present disclosure. Other items shown or discussed as coupled or
directly coupled or communicating with each other may be indirectly
coupled or communicating through some interface, device, or
intermediate component, whether electrically, mechanically, or
otherwise. Other examples of changes, substitutions, and
alterations are ascertainable by one skilled in the art and could
be made without departing from the spirit and scope disclosed
herein.
[0043] While the above detailed description has shown, described,
and pointed out the fundamental novel features of the disclosure as
applied to various implementations, it may be understood that
various omissions and substitutions and changes in the form and
details of the system illustrated may be made by those skilled in
the art, without departing from the intent of the disclosure.
* * * * *