U.S. patent number RE47,913 [Application Number 16/196,492] was granted by the patent office on 2020-03-17 for idle mode access through assisted discovery.
This patent grant is currently assigned to NOKIA TECHNOLOGIES OY. The grantee listed for this patent is NOKIA TECHNOLOGIES OY. Invention is credited to Niko Kiukkonen, Janne Marin, Eng Hwee Ong.
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United States Patent |
RE47,913 |
Ong , et al. |
March 17, 2020 |
Idle mode access through assisted discovery
Abstract
One embodiment is directed to a method of cell
selection/reselection. The method includes gathering discovery
information of a secondary radio access technology (RAT) by
listening to a single primary radio access technology (RAT). The
method may further include performing cell selection/reselection
using the discovery information.
Inventors: |
Ong; Eng Hwee (Espoo,
FI), Marin; Janne (Espoo, FI), Kiukkonen;
Niko (Veikkola, FI) |
Applicant: |
Name |
City |
State |
Country |
Type |
NOKIA TECHNOLOGIES OY |
Espoo |
N/A |
FI |
|
|
Assignee: |
NOKIA TECHNOLOGIES OY (Espoo,
FI)
|
Family
ID: |
47556114 |
Appl.
No.: |
16/196,492 |
Filed: |
November 20, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
13188878 |
Jul 22, 2011 |
9503966 |
Nov 22, 2016 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04W
48/10 (20130101); H04W 48/10 (20130101); H04W
52/0241 (20130101); H04W 52/0241 (20130101); H04W
36/14 (20130101); Y02D 30/70 (20200801); H04W
88/10 (20130101); H04W 84/045 (20130101); H04W
84/045 (20130101); H04W 36/14 (20130101); H04W
36/0094 (20130101); Y02D 70/1262 (20180101); H04W
48/18 (20130101); Y02D 30/70 (20200801); Y02D
70/142 (20180101); Y02D 70/24 (20180101); H04W
48/18 (20130101); H04W 88/10 (20130101); H04W
36/0094 (20130101) |
Current International
Class: |
H04W
4/00 (20180101); H04W 48/10 (20090101); H04W
48/18 (20090101); H04W 52/02 (20090101); H04W
88/10 (20090101); H04W 36/14 (20090101); H04W
84/04 (20090101); H04W 36/00 (20090101) |
Field of
Search: |
;455/435.1,566,552.1
;370/254 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2117279 |
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Nov 2009 |
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EP |
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2011/019976 |
|
Feb 2011 |
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WO |
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Other References
Chinese Office Action dated Jul. 11, 2018 corresponding to Chinese
Patent Application No. 201280036294.2. cited by applicant .
Chinese Office Action dated Oct. 27, 2016 con-esponding to Chinese
Patent Application No. 201280036294.2. cited by applicant .
Lim, C. et al. `SHARE: seamless handover architecture for 3G-WLAN
roaming environment`. Wireless Networks, Apr. 2009, vol. 15, issue
3, pp. 353-363; sections 4, 5.2; fig. 5; table 1. cited by
applicant .
Doppler, K. et al. `On efficient discovery of next generation local
area networks`. In: IEEE Wireless Communications and Networking
Conference (WCNC). IEEE, 2011 (Mar. 28, 2011), p. 269-274. section
II. cited by applicant .
3GPP TS 36.311 V8.14.0 (Jun. 2011). `3rd Generation Partnership
Project; Technical Specification Group Radio Access network;
Evolved Universal Terrestrial Radio Access (E-UTRA) Radio Resource
Control (RRC); Protocol specification (Release 8)`. 3GPP Standard
(Jun. 24, 2011). p. 99-108. cited by applicant .
International Search Report for corresponding International
Application No. PCT/FI2012/050663, dated Oct. 3, 2012. cited by
applicant .
Written Opinion for corresponding International Application No.
PCT/FI2012/050663, dated Oct. 3, 2012. cited by applicant .
3GPP TS 36.211 V10.1.0 Technical Specification, 3rd Generation
Partnership Project; Technical Specification Group Radio Access
Network; Evolved Universal Terrestrial Radio Access; Physical
Channels and Modulation (Release 10), Mar. 2011, pp. 1-103. cited
by applicant .
3GPP TS 36.331 V10.1.0 Technical Specification, 3rd Generation
Partnership Project; Technical Specification Group Radio Access
Network; Evolved Universal Terrestrial Radio Access; Radio Resource
Control; Protocol Specificaiton (Release 10), Mar. 2011, p. 1-290.
cited by applicant .
3GPP TS 36.304 V10.1.0 Technical Specification, 3rd Generation
Partnership Project; Technical Specification Group Radio Access
Network, Evolved Universal Terrestrial Radio Access; User Equipment
Procedures in Idle Mode (Release 10), Mar. 2011, pp. 1-33. cited by
applicant .
3GPP TS 36.213 V10.1.0 Technical Specification, 3rd Generation
Partnership Project; Technical Specification Group Radio Access
Network; Evolved Universal Terrestrial Radio Access; Physical Layer
Procedures (Release 10), Mar. 2011, pp. 1-115. cited by applicant
.
IEEE Standard for Information Technology; Telecommunications and
Information Exchange Between Systems; Local and Metropolitan Area
Networks; Specific Requirements; Part 11: Wireless LAN Medium
Access Control (MAC) and Physical Layer (PHY) Specifications, IEEE
Computer Society, IEEE Std 802.11, Jun. 12, 2007, pp. 1-1233. cited
by applicant .
Zhigang Cao, et al., "WLAN Discovery Scheme Delay Analysis and Its
Enhancement for 3GPP WLAN Interworking Networks", vol. 90B, No. 6,
IEICE Transactions on Communication, vol. E90-B (Jun. 2007), pp.
1523-1527. cited by applicant .
European Search Report issued on Apr. 10, 2015, for corresponding
European Patent Appln. No. 12818178.1. cited by applicant .
European Patent Office, European Search Report for corresponding
European Patent Application No. 12818178.1, dated Jul. 28, 2015.
cited by applicant.
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Primary Examiner: Escalante; Ovidio
Attorney, Agent or Firm: Squire Patton Boggs (US) LLP
Claims
We claim:
1. A method, comprising: gathering, by a multi-mode device,
discovery information of a secondary radio access technology (RAT)
by listening to a single primary RAT in idle mode, wherein the
discovery information of the secondary RAT is gathered together
with system information of the primary RAT, and wherein the
gathering comprises gathering the discovery information from a dual
mode home NodeB (HNB)/wireless local area network (WLAN) access
point; performing cell selection and/or reselection using the
discovery information without performing an independent cell
search; pre-associating with the secondary RAT by using the
discovery information gathered from the primary RAT; and powering
off an interface used to communicate with the secondary RAT after
pre-association, wherein the .[.multi-mode device.]. .Iadd.dual
mode home NodeB (HNB)/wireless local area network (WLAN) access
point .Iaddend.is informed when the interface used to communicate
with the secondary RAT should be turned on, and wherein the system
information of the primary RAT comprises a physical cell identity
(PCI).
2. The method according to claim 1, further comprising informing
the dual mode access point that the interface has been powered
off.
3. The method according to claim 1, wherein the discovery
information comprises one of wireless local area network (WLAN)
discovery information and home nodeB (HNB) discovery
information.
4. The method according to claim 3, wherein the wireless local area
network (WLAN) discovery information comprises at least one of
timestamp, beacon interval, capability information, and key
information elements including service set identity (SSID),
supported rates, physical layer (PHY) parameter set, and any other
optional information elements.
5. The method according to claim 3, wherein the home nodeB (HNB)
discovery information further comprises at least one master
information block (MIB), key system information including public
land mobile network (PLMN) identity (ID), cell ID, closed
subscriber group (CSG) indication, and CSG ID found in system
information block 1 (SIB 1), radio resource configuration
information and physical random access channel (PRACH)
configuration information found in system information block 2
(SIB2), and CSG-specific PCI range information found in system
information block 4 (SIB4).
6. An apparatus, comprising: at least one processor; and at least
one memory including computer program code; the at least one memory
and the computer program code are configured, with the at least one
processor, to cause the apparatus at least to gather discovery
information of a secondary radio access technology (RAT) by
listening to a single primary RAT in idle mode, wherein the
discovery information of the secondary RAT is gathered together
with system information of the primary RAT, and wherein the
discovery information is gathered from a dual mode home NodeB
(HNB)/wireless local area network (WLAN) access point; perform cell
selection and/or reselection using the discovery information
without performing an independent cell search; pre-associate with
the secondary RAT by using the discovery information gathered from
the primary RAT; and power off an interface used to communicate
with the secondary RAT after pre-association, wherein the
.[.multi-mode device.]. .Iadd.dual mode home NodeB (HNB)/wireless
local area network (WLAN) access point .Iaddend.is informed when
the interface used to communicate with the secondary RAT should be
turned on, and wherein the system information of the primary RAT
comprises a physical cell identity (PCI).
7. The apparatus according to claim 6, wherein the at least one
memory and the computer program code are further configured, with
the at least one processor, to cause the apparatus at least to
inform the dual mode access point that the interface has been
powered off.
8. The apparatus according to claim 6, wherein the discovery
information comprises one of wireless local area network (WLAN)
discovery information and home nodeB (HNB) discovery
information.
9. The apparatus according to claim 8, wherein the wireless local
area network (WLAN) discovery information comprises at least one of
timestamp, beacon interval, capability information, and key
information elements including service set identity (SSID),
supported rates, physical layer (PHY) parameter set, and any other
optional information elements.
10. The apparatus according to claim 8, wherein the home nodeB
(HNB) discovery information further comprises at least one of
master information block (MIB), key system information including
public land mobile network (PLMN) identity (ID), cell ID, closed
subscriber group (CSG) indication, and CSG ID found in system
information block 1 (SIB 1), radio resource configuration
information and physical random access channel (PRACH)
configuration information found in system information block 2
(SIB2), and CSG-specific PCI range information found in system
information block 4 (SIB4).
11. A computer program embodied on a non-transitory computer
readable storage medium, the computer program configured to control
a processor to perform a process, comprising: gathering discovery
information of a secondary radio access technology (RAT) by
listening to a single primary RAT in idle mode, wherein the
discovery information of the secondary RAT is gathered together
with system information of the primary RAT, and wherein the
gathering comprises gathering the discovery information from a dual
mode home NodeB (HNB)/wireless local area network (WLAN) access
point; performing cell selection and/or reselection using the
discovery information without performing an independent cell
search; pre-associating with the secondary RAT by using the
discovery information gathered from the primary RAT; and powering
off an interface used to communicate with the secondary RAT after
pre-association, wherein the .[.multi-mode device.]. .Iadd.dual
mode home NodeB (HNB)/wireless local area network (WLAN) access
point .Iaddend.is informed when the interface used to communicate
with the secondary RAT should be turned on, and wherein the system
information of the primary RAT comprises a physical cell identity
(PCI).
Description
FIELD
Embodiments of the invention relate to a radio or wireless
communications system.
BACKGROUND
In recent years, there has been explosive and increasing demand for
mobile broadband delivery over cellular and wireless networks. As a
result, the need for increasing broadband network capacity becomes
imperative for network operators in order to maintain their annual
capital expenditure (CAPEX) while continuing to offer the same flat
rate data access and remain competitive. One of the key trends is
the deployment of either 3GPP femtocell or wireless local area
network (WLAN) for data offloading. A femtocell or Home NodeB (HNB)
is a small cellular base station, typically designed for use in a
home or small business. Apart from data offloading, femtocell
allows network operators to extend service coverage indoors,
especially where access would otherwise be limited or unavailable.
In 3GPP terminology, a HNB is a 3G femtocell. A Home eNodeB (HeNB)
is a Long Term Evolution (LTE) femtocell. In this disclosure, HNB
will be used to refer to any type of femtocell.
Accordingly, data offloading with HNB or WLAN is a cost-effective
solution to lower the cost of mobile broadband delivery, which is
critical in sustaining the network operator's business model, as
compared to a new macro cell where the cost of deploying a base
station increases by several orders of magnitude. In other words,
data offloading solutions would help to decrease the cost per bit
while maintaining the same monthly bill for end-users.
SUMMARY
One embodiment is directed to a method including gathering
discovery information of a secondary radio access technology (RAT)
by listening to a single primary radio access technology (RAT) in
idle mode, and performing cell selection/reselection using the
discovery information.
Another embodiment is directed to an apparatus including at least
one processor and at least one memory including computer program
code. The at least one memory and the computer program code are
configured, with the at least one processor, to cause the apparatus
at least to gather discovery information of a secondary radio
access technology (RAT) by listening to a single primary radio
access technology (RAT) in idle mode, and perform cell
selection/reselection using the discovery information.
Another embodiment includes a computer program embodied on a
computer readable storage medium. The computer program is
configured to control a processor to perform a process. The process
includes gathering discovery information of a secondary radio
access technology (RAT) by listening to a single primary radio
access technology (RAT) in idle mode, and performing cell
selection/reselection using the discovery information.
Another embodiment is directed to a method including storing
wireless local area network (WLAN) discovery information in a long
term evolution (LTE) system information block (SIB) and mapping the
long term evolution (LTE) system information block (SIB) to a
corresponding long term evolution (LTE) system information (SI)
message, and broadcasting the wireless local area network (WLAN)
discovery information, during a long term evolution (LTE) system
information (SI) window, to at least one mobile device to be used
for cell selection/reselection by the mobile device.
Another embodiment is directed to an apparatus including at least
one processor and at least one memory including computer program
code.
The at least one memory and the computer program code are
configured, with the at least one processor, to cause the apparatus
at least to store wireless local area network (WLAN) discovery
information in a long term evolution (LTE) system information block
(SIB) and map the long term evolution (LTE) system information
block (SIB) to a corresponding long term evolution (LTE) system
information (SI) message, and to broadcast the wireless local area
network (WLAN) discovery information, during a long term evolution
(LTE) system information (SI) window, to at least one mobile device
to be used for cell selection/reselection by the mobile device.
Another embodiment is directed to a method including storing home
nodeB (HNB) discovery information in a vendor specific information
element, and broadcasting the home nodeB (HNB) discovery
information to at least one mobile device to be used for cell
selection/reselection by the mobile device.
Another embodiment is directed to an apparatus including at least
one processor and at least one memory including computer program
code. The at least one memory and the computer program code are
configured, with the at least one processor, to cause the apparatus
at least to store home nodeB (HNB) discovery information in a
vendor specific information element, and broadcast the home nodeB
(HNB) discovery information to at least one mobile device to be
used for cell selection/reselection by the mobile device.
BRIEF DESCRIPTION OF THE DRAWINGS
For proper understanding of the invention, reference should be made
to the accompanying drawings, wherein:
FIG. 1 illustrates an apparatus according to certain embodiments of
the invention;
FIG. 2 illustrates a flowchart of a long term evolution (LTE) cell
search method, according to an embodiment;
FIG. 3 illustrates a flowchart of a wireless local area network
(WLAN) passive/active scanning method, according to an
embodiment;
FIG. 4 illustrates an example of long term evolution (LTE)
frequency division duplex (FDD) frame structure and system
information scheduling, according to an embodiment;
FIG. 5 illustrates an example of a wireless local area network
(WLAN) beacon frame format, according to one embodiment;
FIG. 6 illustrates a flowchart of an initial access or cell
selection method, according to an embodiment;
FIG. 7a illustrates a flowchart of a method of powering on a radio
access technology (RAT) interface, according to an embodiment;
FIG. 7b illustrates a flowchart of a method of powering off a radio
access technology (RAT) interface, according to an embodiment;
and
FIG. 8 illustrates a flowchart of an enhanced cell reselection
method after initial access, according to an embodiment.
DETAILED DESCRIPTION
Although data offloading can be effectuated by HNB and WLAN, they
are often considered as competitive solutions and, hence, exist
independently. Considering the highly complementary characteristics
of HNB and WLAN, the integration of these two technologies within a
single access point would present many compelling optimization
opportunities. As a result, it is expected that such a dual mode
HNB/WLAN access point would be prevalent in the future as their
cross-exploitation benefits become apparent to network operators,
equipment vendors, and end-users. Certain embodiments of the
invention aim to elicit the benefits of such a dual mode HNB/WLAN
access point.
Additionally, with growing global concerns over carbon emission and
carbon footprint reduction, `green` communications have developed
prime importance in the current wireless networking arenas that is
expected to continue into the future. While there have been
numerous initiatives to reduce the carbon footprint of mobile
subscribers from different phases of the mobile communication
lifecycle, such as supply chain, vendor, and end-of-life, little
has been done in the usage phase. Some of the areas where the usage
of today's mobile devices, such as smartphones, can be optimized
include the following: Network discovery such as cell search
procedure of 3GPP, e.g., LTE user equipment (UE) and scanning
procedure of WLAN station (STA). These are one of the most energy
consuming operations among others such as data transmission. Thus,
it may be preferable that network discovery for individual radio
access technology (RAT) is avoided whenever possible. Note that UE
and STA are collectively known as devices hereinafter. LTE cell
search procedure could be more efficient than WLAN passive/active
scanning procedure when the number of channels to be scanned is
limited by using stored information cell selection and measurement
rules for cell reselection, for example. Hence, an intelligent
scheme that switches between different network discovery procedures
would enhance energy efficiency of devices. Powering on, at the
same time, both LTE and WLAN interfaces in devices results in
faster battery drain and, consequently, poor energy efficiency.
Again, a context aware scheme that adaptively powers on/off
interfaces would conserve significant energy. Access points
typically operate in the power on state all the time. However,
there are many instances, such as off-peak hours, night, and
absence of end-users, where access points could be switched off to
save energy.
Furthermore, successful HNB discovery during cell reselection is
dependent on parameters such as intra-frequency threshold
S.sub.IntraSearch for the case when macro cell and HNB share the
same frequency, and inter-frequency threshold S.sub.nonIntraSearch
for the case when macro cell and HNB use different frequencies. It
should be noted that S.sub.IntraSearch and S.sub.nonIntraSearch
reselection thresholds are incorporated in rules to limit the
measurements the UE is required to perform in order to extend its
battery lifetime. Further, in order to control access to HNB, it
can be configured as open, closed, or hybrid access. Some
embodiments of the invention consider HNB from the standpoint of
closed access, also known as closed subscriber group (CSG) cell,
which may be the typical access mode available in 3GPP Release 8.
However, the concepts are easily modified for open access and
similar for hybrid access available in 3GPP Release 9. Therefore,
other embodiments may be directed to open, hybrid, or any other
access scheme.
The optimal settings of the reselection thresholds may be
non-trivial, particularly, for S.sub.nonIntraSearch due to high
adjacent channel interference ratio (ACIR). These could then result
in the inability to trigger cell reselection procedure which
implies that data offloading via HNB becomes ineffective. Thus,
quality of service (QoS) and energy efficiency of devices may also
be degraded.
Although the current 3GPP Release 10 specifications (TS 25.304 and
36.304) introduce the concept of an autonomous search function for
aiding cell reselection from macro cell to HNB, they do not specify
when and/or where to search for allowed CSG cells. Furthermore,
there have been discussions to define new HNB selection criterion
and ranking offset to enable better cell reselection to HNB.
However, these are typically frequency specific parameters which
will affect all cells in that particular frequency. Hence, it is
naturally challenging for such solutions to meet the requirements
of both CSG and non-CSG cells. For example, prioritizing UE to camp
on CSG cell will consume unnecessary energy to constantly search
for CSG cells, even when they are not available. Moreover, these
are still not available in the current 3GPP Release 10
specifications.
Based on the above, embodiments of the invention introduce a more
energy efficient network access, which includes an enhanced cell
selection/reselection procedure, as well as network and device
operation schemes. Moreover, embodiments of the invention improve
the probability of successful HNB discovery to ensure effective
data offloading.
For example, embodiments of the invention facilitate energy
efficient network access and operation schemes by leveraging the
dual mode HNB/WLAN access point through assisted network discovery.
In certain embodiments, energy efficiency during network access, as
well as both network and device operation schemes in the idle mode
are optimized. In addition, some embodiments provide a solution for
guaranteed HNB discovery by leveraging the availability of dual
mode HNB/WLAN access point.
Thus, one embodiment provides a method to reduce the time and,
consequently, energy spent on network discovery, as well as network
and device operation schemes based on usage patterns. Although some
embodiments and examples discussed herein are based on the dual
mode HNB/WLAN access point, other embodiments are readily
applicable to a more general multi-RAT environment. In particular,
embodiments of the invention enable devices to gather discovery
information of secondary RATs by just listening to a single primary
RAT during cell selection/reselection in the idle mode. In this
way, devices will only need to scan the primary RAT once to acquire
system information of the primary and any other secondary RATs.
Unless otherwise stated, certain embodiments assume devices with
multi-mode capability. It should be noted, however, that the same
principles could also be applied for the case of inter-RAT handover
during active mode.
Another embodiment of the invention introduces the second RAT, such
as WLAN, to assist in HNB discovery for data offloading, for
instance, when performing cell reselection from macro cell to HNB.
The utilization of the WLAN interface will enable guaranteed HNB
discovery, particularly, when the cell reselection procedure fails
to be invoked either due to non-optimal S.sub.IntraSearch and
S.sub.nonIntraSearch values or high ACIR when macro cell and HNB
are deployed on different frequencies. It should be noted that cell
reselection from macrocell to femtocell (HNB) is more challenging
than from femtocell to macrocell and femtocell to femtocell. This
is because physical cell identity (PCI) confusion may occur due to
high PCI reuse which may be employed to circumvent the limited size
of the neighbor cell list. PCI confusion occurs, for example, when
the UE detects two neighboring cells of the same PCI values. As a
result, the serving cell does not know which one the UE is
measuring and reporting.
FIG. 1 illustrates an example of a device 10 configured to reduce
the time and energy it spends on network discovery, according to
one embodiment. In some embodiments, device 10 is implemented in an
electronic device, such as a mobile device or user equipment,
including a mobile telephone, smartphone, portable computer, tablet
computer, laptop, notebook, Personal Digital Assistant (PDA),
portable game console, or any other electronic device capable of
communication with a network. In other embodiments discussed below,
device 10 or portions thereof may be implemented in a base station
or access point, such as a dual mode HNB/WLAN access point.
Device 10 may include an interface 12, such as a bus or other
communications mechanism, for communicating information between
components of device 10. Alternatively, the components of device 10
may communicate directly with each other, without use of interface
12.
Device 10 also includes a processor 22, coupled to interface 12,
for receiving, managing, and/or processing network and user input
or information, and for executing instructions or operations.
Processor 22 may be any type of general or specific purpose
processor.
Device 10 further includes a memory 14 for storing information and
instructions to be executed by processor 22. Memory 14 can be
comprised of any combination of random access memory (RAM), read
only memory (ROM), static storage such as a magnetic or optical
disk, or any other type of machine or computer readable media.
Computer readable media may be any available media that can be
accessed by processor 22 and could include volatile or nonvolatile
media, removable or non-removable media, and communication media.
Communication media may include computer program code or
instructions, data structures, program modules or other data, and
includes any information delivery media.
Processor 22 can further be coupled, via interface 12 or directly,
to a graphical user interface or display 24, such as a thin film
transistor (TFT) liquid crystal display (LCD), for displaying
information to a user. In some embodiments, display 24 can be a
touchscreen display that allows a user to interact directly with
what is presented on display 24 by using their finger, hand,
stylus, or another passive object. A keypad 26 can further be
coupled to interface 12 to enable a user to interface with device
10. In one example, keypad 26 is a touchscreen keypad displayed on
display 24 where each of the keys can be activated by touching that
portion of display 24. Alternatively, keypad 26 may be a physical
keypad.
Device 10 can further include a sensor or detector 20 for detecting
some action taken, for example, by a user by means of display 24 or
keypad 26. Detector 20 can be a separate component of device 10 or,
alternatively, detector 20 can be included as a function of
processor 22.
In one embodiment, memory 14 stores software modules or
applications that provide functionality when executed by processor
22. The modules may include an operating system 15 that provides
operating system functionality for device 10. The memory 14 may
also store applications 16, such as text editing or messaging
applications, games, web browsers, etc.
According to certain embodiments, device 10 is configured to
perform an energy efficient method of cell selection or
reselection. Therefore, one embodiment introduces the notion of
energy efficient initial access, as well as network and device
operation schemes based on assisted network discovery. In this
embodiment, assisted network discovery means that the discovery
information of the secondary RAT is broadcasted together with the
system information of the primary RAT. In an embodiment, the
discovery information is broadcast by an access point, which may be
a dual mode access point such as a HNB/WLAN access point. Further,
it is noted that the optimization of energy consumption in network
and device operation schemes is also based on their usage
patterns.
FIG. 2 illustrates a flowchart of assisted network discovery in a
LTE system, according to one embodiment. In certain embodiments,
the functionality of the flowchart of FIG. 2, and FIGS. 3, 6 to 8
discussed below, are implemented by software stored in memory 14 or
other computer readable or tangible media, and executed by
processor 22 of device 10. In other embodiments, the functionality
may be performed by hardware (e.g., through the use of an
application specific integrated circuit (ASIC), a programmable gate
array (PGA), a field programmable gate array (FPGA), etc.), or any
combination of hardware and software.
Referring to FIG. 2, at 200, the cell search procedure is started.
The cell search procedure of LTE as shown in FIG. 2 can be invoked
by a cell selection procedure that occurs when device 10 powers on
or recovers from lack of coverage, and/or a cell reselection
procedure to search for a better cell after device 10 has gained
initial access. At 201, a (next) carrier frequency is selected for
cell selection or reselection. As part of the cell search
procedure, device 10 will need to perform initial synchronization
to detect a LTE cell and decode all information required for
registering to it. LTE employs a hierarchical cell search scheme
whereby its synchronization sequences are divided into primary
synchronization signal (PSS) and secondary synchronization signal
(SSS). At 202, PSS is detected and, at 203, SSS is detected. The
PCI is then derived, at 204, from PSS which contains three possible
values to identify the PCI and SSS which contains 168 possible
values to identify the PCI group.
At 205, device 10 determines whether it is an initial access case.
For initial access cases, device 10 will proceed, at 217, to decode
the physical broadcast channel (PBCH) and, at 218, to decode the
physical downlink shared channel (PDSCH) to acquire the master
information block (MIB), and system information block 1 (SIB 1)
which contains key information. The key information may include
public land mobile network (PLMN) identity (ID) and cell ID, from
which the cell global identity (CGI) can be derived, CSG
indication, and CSG ID. At 219, device 10 determines whether the
PLMN is allowed. With the PLMN ID, the device will know if it
belongs to that available PLMN based on the PLMN saved in the
universal subscriber identity module (USIM). If device 10 does not
belong to the available PLMN, the flow returns to 201. If, however,
device 10 belongs to the available PLMN, at 220, device 10 selects
the new PLMN for visited PLMN (VPLMN) cases. Then, at 221, device
10 obtains scheduling information of system information (SI)
messages from SIB1.
At 222, device 10 reads SI messages SIB2 and SIB4 to acquire radio
resource configuration information, PRACH configuration
information, and csg-PhysCellIdRange. Device 10 may also read any
other SI messages, ranging from SIB2 through SIB 13, if necessary.
At 223, device 10 performs cell selection procedure to determine
whether a suitable cell could be found. If no suitable cell could
be found, then, at 215, device 10 camps on any cell. If a suitable
cell has been found, then, at 224, device 10 camps normally on a
target cell which satisfies the S criterion. If the target cell is
a CSG cell, then device 10 may need to perform an additional CSG ID
check to avoid camping on an unauthorized HNB. At 225, device 10
obtains and stores timestamp, beacon interval, capability
information, and necessary information elements from SI message
that corresponds to SIB9 (WLAN discovery information) to access
WLAN. Then, at 226, the cell search ends.
In the case of non-initial access, device 10 may identify, at 206,
whether a target cell is a CSG cell. Note that it is possible to
differentiate between a CSG and non-CSG cell based on the stored
CSG-specific PCI range (csg-PhysCellIdRange) in block 222, which is
valid for 24 hours, without extracting specific CSG information by
reading SIBs of the measure neighboring cells. At 207, device 10
determines whether it has a valid CSG subscription. If device 10
has a valid CSG subscription (non-empty CSG whitelist), then it can
perform CSG cell search, at 212, by using the autonomous search
function which may ignore a non-CSG cell, at 214. After performing
the autonomous search function, at 213, it is determined whether
the target cell is a CSG cell. On the other hand, if device 10 does
not have a valid CSG subscription, then it may ignore, at 208, CSG
cell in its cell ranking during the cell reselection procedure.
These are ways for device 10 to prioritize the handling of CSG cell
and save battery power during CSG cell search.
Further, for non-initial access cases, device 10 need not decode
PBCH and PDSCH, but rather it performs, at 209, measurements such
as reference signal received power (RSRP) and reference signal
received quality (RSRQ) based on the reference signal (RS) of
neighboring cells. At 210, device 10 performs cell reselection
procedure to determine whether a suitable cell could be found. At
211, a suitable cell which maximizes the R criterion will then be
reselected as the new serving cell. Similarly, if the target cell
is a CSG cell, then device 10 may need to perform an additional CSG
ID check to avoid reselecting an unauthorized HNB. In both initial
access and non-initial access cases, device 10 will camp, at 215,
on any cell where only emergency calls are allowed in the connected
mode when no suitable and acceptable cell was found. The cell
search procedure ends at 226.
Thus, embodiments of the invention include the broadcast WLAN
discovery information which may include timestamp, beacon interval,
capability information, and necessary information elements to
assist device in accessing WLAN system without performing
independent cell search in block 225. This implies that battery
power of devices associated with scanning WLAN can be optimized. It
is worth mentioning that the necessary information elements may
include key information elements such as service set identity
(SSID), supported rates, and physical layer (PHY) parameter set,
and any other optional information elements. For example, the
optional information elements may be present to support high
throughput (HT) and very high throughput (VHT) functionalities by
including the HT capabilities and HT operation, as well as VHT
capabilities and VHT operation, respectively.
FIG. 3 illustrates a flowchart of assisted network discovery in a
WLAN system, according to one embodiment. At 300, the cell search
procedure of WLAN is started. At 301, device 10 decides whether to
perform passive scanning or active scanning. The device 10 may, at
303, perform passive scanning on each channel for a beacon interval
of typically 100 ms if it has no prior knowledge about any existing
WLANs. Hence, the time and energy spent will increase linearly with
the number of channels to be scanned. On the other hand, the device
10 may perform, at 302, active scanning through additional probe
request/response frame exchanges if it knows the SSID of a specific
WLAN that it is trying to access. Note that the device may also
perform active scanning by using a wildcard SSID, i.e.,
non-specific SSID. However, such active scanning will not detect
hidden WLAN.
After detecting the beacon frame at 303 when performing passive
scanning or performing active scanning at 302, device 10 may
acquire, at 304, fixed field information such as timestamp, beacon
interval, and capability information. Device 10 may further
acquire, at 305, key variable length information elements such as
service set identifier (SSID), supported rates, PHY parameter set,
and other optional information elements, if any.
Embodiments of the invention include the broadcast of HNB discovery
information which may include PCI, MIB, PLMN ID and cell ID from
which the CGI can be derived, CSG indication, CSG ID,
csg-PhysCellIdRange, radio resource configuration information, and
physical random access channel (PRACH) configuration information to
assist device 10 in accessing LTE system without performing
independent cell search which includes the measurement of
neighboring cells in the case of cell reselection procedure.
Similarly, this implies that battery power of devices associated
with scanning LTE can be optimized.
Thus, referring to FIG. 3, at 306, device 10 reads the vendor
specific information element and, at 307 acquires the HNB discovery
information. At 308, device 10 obtains and stores PCI, MIB, PLMN
ID, cell ID, CSG indication, CSG ID, csg-PhysCellIdRange, radio
resource configuration information, and PRACH configuration
information to access the HNB. The cell search then ends at
309.
Embodiments of the invention also provide examples of how discovery
information of the secondary RAT can be broadcasted together with
system information of the primary RAT. In some embodiments, the
discovery information shown in FIG. 4, and FIG. 5 discussed below,
may be broadcast by a dual-mode HNB/WLAN or a multi-mode access
point.
FIG. 4 illustrates an example of a LTE frequency division duplex
(FDD) frame structure, master information block (MIB), system
information block 1 (SIB 1), and scheduling of other system
information messages in which WLAN discovery information is
contained in system information block 9 (SIB9). For example, FIG. 4
illustrates WLAN discovery information 400 that is scheduled to be
transmitted in the LTE SI message (SIB 9) 410. FIG. 5 illustrates
HNB discovery information 500 that is transmitted in the vendor
specific information element 510 of WLAN beacon.
The LTE system information in FIG. 4 may be transmitted based on
time scheduling. The MIB and SIB 1 messages have fixed
periodicities of 40 ms and 80 ms, respectively. Additionally, the
MIB is repeated in subframe #0 (1 subframe=1 ms) of every radio
frame (1 radio frame=10 ms), while SIB1 is repeated in subframe #5
of every other radio frame. The MIB contains the system frame
number (SFN) which functions as a running counter of the radio
frames. On the other hand, the scheduling of SI messages may be
more flexible. Each SI message is transmitted in a specific
scheduling window known as the SI-window with a predefined
periodicity. The SI-windows of different SI messages are
consecutive and have a common configurable length. Within each
SI-window, the corresponding SI message can be transmitted multiple
times over different subframes. However, no SI message can be
transmitted in subframes that are used for SIB1 and uplink time
division duplex (TDD) transmissions. According to one embodiment,
the WLAN discovery information 400 may be stored in SIB 9 which
currently contains the name of HNB for display on devices during
manual CSG selection.
The WLAN information element in FIG. 5 is a flexible data structure
that occurs in the frame body in order of increasing identifiers.
It contains an information identifier, a length, and the content of
the information element. The vendor specific information set 510
contains an additional mandatory field known as the
organizationally unique identifier that distinguishes between
vendors. In one embodiment, the HNB discovery information 500 may
be stored in the variable vendor specific information field which
can accommodate up to 252 octets of information.
One embodiment specifies that devices always perform the cell
search procedure, upon powering on or upon recovery from lack of
coverage, using the RAT of wide area coverage, such as LTE. FIG. 6
illustrates a flowchart of a cell selection procedure upon the
powering on of devices in the vicinity of the dual mode HNB/WLAN
access point, according to an embodiment. As depicted in FIG. 6,
the cell search procedure starts upon power on at 600. At 601, it
is determined whether the station is a WLAN only STA. If it is a
WLAN only STA, then, at 602, cell search is performed using WLAN
interface and, at 603, the device associates with WLAN.
According to an embodiment, if the device is not a WLAN only STA,
then the device may perform cell search, at 604, by using LTE as
the default interface so that idle mode mobility to macro cell, for
example, will not be affected. At 605, it is determined whether the
device supports multi-mode capability. If so, the device may
acquire, at 606, the discovery information of the secondary RAT,
such as WLAN. After cell selection at 607 and confirming that a
suitable cell was found at 609, the device may camp normally on HNB
at 610. Multi-mode device may pre-associate with WLAN, at 611.
After which, the multi-mode device can power off the WLAN interface
at 612 to save energy, and inform the HNB/WLAN access point
accordingly at 613. If no suitable and acceptable cell was found at
609, then the device may camp on any cell at 608. However, for
multi-mode device, it may also associate with WLAN at 603 by using
the discovery information acquired at 606. The cell search
procedure ends at 614. It should be noted that the energy savings
here is twofold. First, devices only need to perform an LTE cell
search procedure to acquire system information of both HNB and
WLAN. Second, devices can power off their WLAN interface after
pre-association.
FIG. 7a illustrates a method for devices to selectively power on
the secondary RAT interface, such as WLAN, only when required and
when its corresponding RAT exists in the device's coverage region,
according to one embodiment. Specifically, as illustrated in FIG.
7a, the WLAN interface is off at 700 and, at 710, it is determined
whether the WLAN interface in the device should be powered on. When
it is determined that the WLAN interface should be powered on, the
HNB/WLAN access point is informed to power on WLAN interface. The
WLAN interface could be powered on for the purpose of best effort
services, interference mitigation, capacity enhancements, and
`ping-pong` handover mitigation, amongst others on the condition
that a WLAN access point exists in the vicinity. The availability
of secondary RAT can be implied by the existence of its discovery
information while listening to the primary RAT. The WLAN interface
in the device in on at 730.
FIG. 7b illustrates a method for the dual mode HNB/WLAN access
point to power off the secondary RAT, such as WLAN interface, to
save energy when there is either no WLAN only device in its
coverage region or the inactivity timer of all WLAN only devices
have expired, according to an embodiment. As illustrated in FIG.
7b, the WLAN interface is on at 740. At 750, it is determined
whether a WLAN only STA is present. If a WLAN only STA is present,
then it is determined, at 760, whether the inactivity timer has
expired. If the inactivity timer has not expired, then the flow
returns to 740. If no WLAN only STA is present or if the inactivity
timer has expired, then, at 770, the WLAN interface in the HNB/WLAN
access point is powered off. FIG. 7b does not serve to limit the
decision mechanisms for powering off WLAN interface. For example,
the WLAN interface may be powered off during specific times of the
day such as at night. On the other hand, it may not be powered off
when it is required to assist in HNB discovery as discussed below.
The powering off of WLAN interface in the dual mode HNB/WLAN access
point is possible now as the primary RAT, such as LTE, will assist
in announcing its existence.
Another embodiment is directed to the concept of utilizing the
second RAT, such as WLAN, to assist in the discovery of HNB. This
will ensure guaranteed successful HNB discovery in order to
facilitate data offloading. FIG. 8 illustrates a flowchart of the
enhanced cell reselection procedure in the vicinity of the HNB/WLAN
access point, according to one embodiment.
According to this embodiment, the device can perform cell
reselection from macro cell to HNB by using WLAN as the default
interface. Note that devices would know that HNB is in their
vicinity as CSG cell will broadcast, in SIB1, the CSG indication
flag and CSG ID, which are valid for up to 3 hours. Moreover, the
range of PCI values that are used for CSG cell is broadcasted as
the csg-PhysCellIdRange parameter, which is valid for up to 24
hours, in SIB4. The macro cell can also be optionally configured to
broadcast the csg-PhysCellIdRange parameter. These are various
means available in 3GPP Release 10 to assist devices in CSG cell
search as specified in 3GPP TS 36.331 and TS 36.304.
As illustrated in FIG. 8, the new cell identification begins at
800. At 801, it is determined whether the device supports
multi-mode capability. If it is not a multi-mode device, then, at
805, it is determined whether
Squal<SIntraSearchQ/SnonIntraSearchQ. If so, cell search is
performed using LTE interface at 807, and the flow proceeds to
trigger cell reselection at 808 discussed below. If the
determination at 805 is negative, then the flow proceeds to the
next DRX cycle at 806.
If the device supports multi-mode capability, it could then power
on its WLAN interface at 802. At 803, the device may perform cell
search using the WLAN interface, and acquire, at 804, HNB discovery
information when it is in the proximity of CSG cells. For security
concerns, the device may use the knowledge of a secure WLAN SSID to
verify the authenticity of the HNB discovery information. Moreover,
the LTE and WLAN interfaces are collocated in the same access point
which means that discovery information of the second RAT would be
reliable.
At 808, the device performs cell reselection and, at 809,
determines if a suitable cell was found. If no suitable and
acceptable cell was found, then the device, at 810, may camp on any
cell. However, for multi-mode device, it may also associate with
WLAN at 820 by using the WLAN system information acquired at 803.
If The HNB is selected as the new serving cell at 811 if it was
found to be a suitable cell. Similarly, for multi-mode device, it
may pre-associate with WLAN, at 812. After which, to save energy,
the multi-mode device can power off its WLAN interface, at 813, and
inform, at 814, the HNB/WLAN access point accordingly. The new cell
identification ends at 815.
Such assisted HNB discovery would not generate extra interferences
to the LTE system, for example, by reselecting to a cell which is
not the best ranked cell, since HNB would likely be the highest
ranked cell of its frequency in a home scenario where end-users are
residing. In addition, according to certain embodiments, no
measurement of neighboring cells is required in the cell
reselection procedure which leads to significant improvement in
energy efficiency.
As a result of the embodiments discussed herein, there will be a
significant reduction in latency and energy consumption associated
with cell selection/reselection when discovery information of
secondary RATs can be acquired by listening to a primary RAT. This
implies that devices need not scan the entire frequency band of
each RAT in order to look for critical system information such as
PLMN ID, CGI, CSG ID, SSID, etc. The initial access via cellular
networks, such as LTE, maintains its advantage of idle mode
mobility of macro cell to HNB, HNB to macro cell, and between HNBs.
Devices can save energy by powering on only the relevant RAT
interface according to its geolocation, applications, and
requirements. Access points can also save energy by powering off
interfaces at instances where it may not be required.
Embodiments of the invention also guarantee successful HNB
discovery for effective data offloading which would otherwise
result in QoS and energy efficiency degradation. Further, the need
for heavy measurement of neighboring cells during cell reselection
from macro cell to HNB is eliminated, which leads to substantial
energy savings. Embodiments of the invention will greatly benefit
multi-mode devices, supported by either software defined radio
(SDR) reconfigurability or multiple transceivers, in terms of
improved latency and energy efficiency. In addition, embodiments of
the invention support backward compatibility for single-mode
devices.
The described features, advantages, and characteristics of the
invention may be combined in any suitable manner in one or more
embodiments. One skilled in the relevant art will recognize that
the invention can be practiced without one or more of the specific
features or advantages of a particular embodiment. In other
instances, additional features and advantages may be recognized in
certain embodiments that may not be present in all embodiments of
the invention.
Therefore, one having ordinary skill in the art will readily
understand that the invention as discussed above may be practiced
with steps in a different order, and/or with hardware elements in
configurations which are different than those which are disclosed.
Therefore, although the invention has been described based upon
these preferred embodiments, it would be apparent to those of skill
in the art that certain modifications, variations, and alternative
constructions would be apparent, while remaining within the spirit
and scope of the invention. In order to determine the metes and
bounds of the invention, therefore, reference should be made to the
appended claims.
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