U.S. patent application number 13/569901 was filed with the patent office on 2013-02-14 for apparatuses and methods for handovers between heterogeneous networks.
This patent application is currently assigned to HTC CORPORATION. The applicant listed for this patent is Hsi-Kun CHEN, Peter CHOU. Invention is credited to Hsi-Kun CHEN, Peter CHOU.
Application Number | 20130040693 13/569901 |
Document ID | / |
Family ID | 47677855 |
Filed Date | 2013-02-14 |
United States Patent
Application |
20130040693 |
Kind Code |
A1 |
CHEN; Hsi-Kun ; et
al. |
February 14, 2013 |
Apparatuses and methods for handovers between heterogeneous
networks
Abstract
A mobile communication device is provided with a plurality of
processing logic units. A first processing logic unit is configured
to connect the mobile communication device to a first wireless
network for wireless transceiving via a first link. A second
processing logic unit is configured to determine whether a second
link to a second wireless network is available in response to
detecting a low performance condition of the first link.
Particularly, the first wireless network and the second wireless
network are heterogeneous networks. A third processing logic unit
is configured to hand over the mobile communication device from the
first wireless network to the second wireless network in response
to a transceiving rate of the second link being greater than a
first value.
Inventors: |
CHEN; Hsi-Kun; (Taoyuan
City, TW) ; CHOU; Peter; (Taoyuan City, TW) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CHEN; Hsi-Kun
CHOU; Peter |
Taoyuan City
Taoyuan City |
|
TW
TW |
|
|
Assignee: |
HTC CORPORATION
Taoyuan City
TW
|
Family ID: |
47677855 |
Appl. No.: |
13/569901 |
Filed: |
August 8, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61522045 |
Aug 10, 2011 |
|
|
|
Current U.S.
Class: |
455/525 |
Current CPC
Class: |
H04W 36/30 20130101;
H04W 88/06 20130101; H04W 36/14 20130101 |
Class at
Publication: |
455/525 |
International
Class: |
H04W 36/30 20090101
H04W036/30; H04W 36/14 20090101 H04W036/14 |
Claims
1. A mobile communication device, comprising: a first processing
logic unit configured to connect the mobile communication device to
a first wireless network for wireless transceiving via a first
link; a second processing logic unit configured to determine
whether a second link to a second wireless network is available in
response to detecting a low performance condition of the first
link, wherein the first wireless network and the second wireless
network are heterogeneous networks; and a third processing logic
unit configured to hand over the mobile communication device from
the first wireless network to the second wireless network in
response to a transceiving rate of the second link being greater
than a first value.
2. The mobile communication device of claim 1, wherein the low
performance condition of the first link is obtained according to a
transceiving rate of the first link or a signal quality of the
first wireless network.
3. The mobile communication device of claim 2, wherein the low
performance condition of the first link indicates that the
transceiving rate of the first link is lower than a second value or
the signal quality of the first wireless network is lower than a
predetermined threshold.
4. The mobile communication device of claim 1, wherein the first
wireless network is a non-cellular network and the second wireless
network is a cellular network.
5. The mobile communication device of claim 4, wherein the
non-cellular network is a Wireless Local Area Network (WLAN),
Bluetooth Personal Area Network (BT PAN), or ZigBee Wireless PAN
(ZigBee WPAN).
6. A method for a mobile communication device to handover between a
plurality of heterogeneous networks, comprising: connecting to a
first wireless network for wireless transceiving via a first link;
determining whether a second link to a second wireless network is
available in response to detecting a low performance condition of
the first link, wherein the first wireless network and the second
wireless network are heterogeneous networks; and handing over the
mobile communication device from the first wireless network to the
second wireless network in response to a transceiving rate of the
second link being greater than a first value.
7. The method of claim 6, wherein the low performance condition of
the first link is detected according to a transceiving rate of the
first link or a signal quality of the first wireless network.
8. The method of claim 7, wherein the low performance condition of
the first link indicates that the transceiving rate of the first
link is lower than a second value or the signal quality of the
first wireless network is lower than a predetermined threshold.
9. The method of claim 6, wherein the first wireless network is a
non-cellular network and the second wireless network is a cellular
network.
10. The method of claim 9, wherein the non-cellular network is a
Wireless Local Area Network (WLAN), Bluetooth Personal Area Network
(BT PAN), or ZigBee Wireless PAN (ZigBee WPAN).
11. A mobile communication device, comprising: a first processing
logic unit configured to connect the mobile communication device to
a first wireless network for wireless transceiving via a first
link; a second processing logic unit configured to scan for a
nearby second wireless network with a current signal quality,
wherein the first wireless network and the second wireless network
are heterogeneous networks; a third processing logic unit
configured to apply a condition check on the current signal quality
of the second wireless network according to a result of whether the
mobile communication device was previously connected to the second
wireless network prior to being connected to the first wireless
network; and a fourth processing logic unit configured to hand over
the mobile communication device from the first wireless network to
the second wireless network in response to passing of the condition
check.
12. The mobile communication device of claim 11, wherein the step
of handing over the mobile communication device further comprises:
connecting to the second wireless network via a second link; and
disconnecting with the first wireless network.
13. The mobile communication device of claim 11, wherein the
condition check comprises: determining whether the current signal
quality of the second wireless network is greater than a
predetermined threshold, if the mobile communication device was not
previously connected to the second wireless network prior to being
connected to the first wireless network; and determining whether
the current signal quality of the second wireless network is
greater than the sum of a previous signal quality of the second
wireless network, which was obtained when the mobile communication
device was previously connected to the second wireless network
prior to being connected to the first wireless network, and a
margin value for eliminating a ping-pong effect.
14. The mobile communication device of claim 11, wherein the first
wireless network is a cellular network and the second wireless
network is a non-cellular network.
15. The mobile communication device of claim 14, wherein the
non-cellular network is a Wireless Local Area Network (WLAN),
Bluetooth Personal Area Network (BT PAN), or ZigBee Wireless PAN
(ZigBee WPAN).
16. A method for a mobile communication device to handover between
a plurality of heterogeneous networks, comprising: connecting to a
first wireless network for wireless transceiving via a first link;
scanning for a nearby second wireless network with a current signal
quality, wherein the first wireless network and the second wireless
network are heterogeneous networks; applying a condition check on
the current signal quality of the second wireless network according
to a result of whether the mobile communication device was
previously connected to the second wireless network prior to being
connected to the first wireless network; and handing over the
mobile communication device from the first wireless network to the
second wireless network in response to passing of the condition
check.
17. The method of claim 16, wherein the step of handing over the
mobile communication device further comprises: connecting to the
second wireless network via a second link; and disconnecting with
the first wireless network.
18. The method of claim 16, wherein the condition check comprises:
determining whether the current signal quality of the second
wireless network is greater than a predetermined threshold, if the
mobile communication device was not previously connected to the
second wireless network prior to being connected to the first
wireless network; and determining whether the current signal
quality of the second wireless network is greater than the sum of a
previous signal quality of the second wireless network, which was
obtained when the mobile communication device was previously
connected to the second wireless network prior to being connected
to the first wireless network, and a margin value for eliminating a
ping-pong effect.
19. The method of claim 16, wherein the first wireless network is a
cellular network and the second wireless network is a non-cellular
network.
20. The method of claim 19, wherein the non-cellular network is a
Wireless Local Area Network (WLAN), Bluetooth Personal Area Network
(BT PAN), or ZigBee Wireless PAN (ZigBee WPAN).
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This Application claims priority of U.S. Provisional
Application No. 61/522,045, filed on Aug. 10, 2011, and the
entirety of which is incorporated by reference herein.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The invention generally relates to handovers in the field of
wireless communications, and more particularly, to apparatuses and
methods for handovers between heterogeneous networks to improve the
performance of wireless transceiving.
[0004] 2. Description of the Related Art
[0005] With growing demand for ubiquitous computing and networking,
various wireless technologies have been developed, such as the
Wireless Fidelity (WiFi) technology, Global System for Mobile
communications (GSM) technology, General Packet Radio Service
(GPRS) technology, Enhanced Data rates for Global Evolution (EDGE)
technology, Wideband Code Division Multiple Access (WCDMA)
technology, Code Division Multiple Access 2000 (CDMA-2000)
technology, Time Division-Synchronous Code Division Multiple Access
(TD-SCDMA) technology, Worldwide Interoperability for Microwave
Access (WiMAX) technology, Long Term Evolution (LTE) technology,
Time-Division LTE (TD-LTE) technology, and others. For user
convenience and flexibility, most Mobile Stations (MSs) nowadays
are equipped with more than one wireless communication module for
supporting different wireless technologies. However, each wireless
technology has its own features, such as bandwidth, average
coverage, and service rate, etc. Particularly, the bandwidth and
coverage provided to an MS by a wireless network may vary according
to the location conditions of the MS and/or the time condition.
[0006] Take an MS operating in either an Android or a Windows
system, which supports WiFi and WCDMA technologies, for example.
The MS always selects a WiFi network over a WCDMA network, even if
the signal quality of the WiFi network is bad while the signal
quality of the WCDMA network is fair/good. That is, the MS is
configured to stay connected with the WiFi network with bad signal
quality, regardless of the availability of the WCDMA network with
fair/good signal quality. In such circumstances, even browsing a
web page may take a long time, and accordingly, the user may
experience a serious delay of wireless connectivity. Thus, to
improve the performance of wireless transceiving, it is desirable
to provide smart handovers between heterogeneous networks.
BRIEF SUMMARY OF THE INVENTION
[0007] In one aspect of the invention, a mobile communication
device is provided. The mobile communication device comprises a
first processing logic unit, a second processing logic unit, and a
third processing logic unit. The first processing logic unit is
configured to connect the mobile communication device to a first
wireless network for wireless transceiving via a first link. The
second processing logic unit is configured to determine whether a
second link to a second wireless network is available in response
to detecting a low performance condition of the first link, wherein
the first wireless network and the second wireless network are
heterogeneous networks. The third processing logic unit is
configured to hand over the mobile communication device from the
first wireless network to the second wireless network in response
to a transceiving rate of the second link being greater than a
first value.
[0008] In another aspect of the invention, a method for a mobile
communication device to handover between a plurality of
heterogeneous networks is provided. The method comprises the steps
of connecting to a first wireless network for wireless transceiving
via a first link, determining whether a second link to a second
wireless network is available in response to detecting a low
performance condition of the first link, wherein the first wireless
network and the second wireless network are heterogeneous networks,
and handing over the mobile communication device from the first
wireless network to the second wireless network in response to a
transceiving rate of the second link being greater than a first
value.
[0009] In yet another aspect of the invention, a mobile
communication device is provided. The mobile communication device
comprises a first processing logic unit, a second processing logic
unit, a third processing logic unit, and a fourth processing logic
unit. The first processing logic unit is configured to connect the
mobile communication device to a first wireless network for
wireless transceiving via a first link. The second processing logic
unit is configured to scan for a nearby second wireless network
with a current signal quality, wherein the first wireless network
and the second wireless network are heterogeneous networks. The
third processing logic unit is configured to apply a condition
check on the current signal quality of the second wireless network
according to a result of whether the mobile communication device
was previously connected to the second wireless network prior to
being connected to the first wireless network. The fourth
processing logic unit is configured to hand over the mobile
communication device from the first wireless network to the second
wireless network in response to passing of the condition check.
[0010] In still another aspect of the invention, a method for a
mobile communication device to handover between a plurality of
heterogeneous networks is provided. The method comprises the steps
of connecting to a first wireless network for wireless transceiving
via a first link, scanning for a nearby second wireless network
with a current signal quality, wherein the first wireless network
and the second wireless network are heterogeneous networks,
applying a condition check on the current signal quality of the
second wireless network according to a result of whether the mobile
communication device was previously connected to the second
wireless network prior to being connected to the first wireless
network, and handing over the mobile communication device from the
first wireless network to the second wireless network in response
to passing of the condition check.
[0011] Other aspects and features of the present invention will
become apparent to those with ordinarily skill in the art upon
review of the following descriptions of specific embodiments of the
mobile communication devices and the methods for a mobile
communication device operating as an MS to handover between a
plurality of heterogeneous networks.
BRIEF DESCRIPTION OF DRAWINGS
[0012] The invention can be more fully understood by reading the
subsequent detailed description and examples with references made
to the accompanying drawings, wherein:
[0013] FIG. 1 is a block diagram of a wireless communications
environment according to an embodiment of the invention;
[0014] FIG. 2 is a block diagram illustrating an exemplary software
architecture of the mobile communication device 110 according to an
embodiment of the invention;
[0015] FIG. 3 is a block diagram illustrating an exemplary software
architecture of the mobile communication device 110 according to
another embodiment of the invention;
[0016] FIG. 4 is a state transition diagram illustrating state
machine operations of the mobile communication device 110 according
to an embodiment of the invention;
[0017] FIG. 5 is a schematic diagram illustrating the ping-pong
effect for the mobile communication device 110 wandering around the
coverage edge of the WLAN 130 and the coverage of the cellular
network 120;
[0018] FIG. 6 is a flow chart illustrating a smart handover method
for handing over the mobile communication device 110 from the
cellular network 120 to the WLAN 130 according to an embodiment of
the invention;
[0019] FIG. 7 is a curve diagram illustrating a 2-stage monitoring
for the signal quality of nearby WLANs according to an embodiment
of the invention;
[0020] FIG. 8A is a schematic diagram illustrating RSSI changes for
inward movement towards a WLAN according to an embodiment of the
invention;
[0021] FIG. 8B is a schematic diagram illustrating RSSI changes for
outward movement from a WLAN according to an embodiment of the
invention;
[0022] FIG. 9 is a flow chart illustrating a smart handover method
for handing over the mobile communication device 110 from the WLAN
130 to the cellular network 120 according to an embodiment of the
invention; and
[0023] FIG. 10 is a curve diagram illustrating a 2-stage monitoring
for the signal quality of nearby WLANs according to another
embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0024] The following description is of the best-contemplated mode
of carrying out the invention. This description is made for the
purpose of illustrating the general principles of the invention and
should not be taken in a limiting sense. It should be understood
that the embodiments may be realized in software, hardware,
firmware, or any combination thereof.
[0025] FIG. 1 is a block diagram of a wireless communications
environment according to an embodiment of the invention. The
wireless communications environment 100 comprises a mobile
communication device 110, a cellular network 120 and a non-cellular
network 130. The mobile communication device 110 may selectively
connect to one or both of the cellular network 120 and the
non-cellular network 130 for obtaining wireless services. The
cellular network 120 may be a GSM system, GPRS system, WCDMA
system, CDMA-2000 system, TD-SCDMA system, WiMAX system, LTE
system, or TD-LTE system, etc., depending on the Radio Access
Technology (RAT) in use. The cellular network 120 comprises at
least one cellular station 121 (or so-called base station or access
station), at least one control node 122, and a core network 123,
wherein the cellular station 121 is controlled by the control node
122 to provide the functionality of wireless transceiving for the
cellular network 120, and the cellular station 121 and the control
node 122 together may be referred to as a radio access network or
access network. For example, if the cellular network 120 is a WCDMA
system, the cellular station 121 may be a NodeB, the control node
122 may be a Radio Network Controller (RNC), and the core network
123 may be a General Packet Radio Service (GPRS) core which
includes a Home Location Register (HLR), at least one Serving GPRS
Support Node (SGSN), and at least one Gateway GPRS Support Node
(GGSN). Alternatively, the cellular network 120 may not comprise
any control node. For example, if the cellular network 120 is an
LTE system, the cellular station 121 may be an Evolved-NodeB
(E-NodeB), and the core network 123 may be an Evolved Packet Core
(EPC) which includes a Home Subscriber Server (HSS), Mobility
Management Entity (MME), Serving Gateway (S-GW), and Packet Data
Network Gateway (PDN-GW or P-GW).
[0026] The non-cellular network 130 may be a Wireless Local Area
Network (WLAN), a Bluetooth Personal Area Network (BT PAN), ZigBee
Wireless PAN (ZigBee WPAN), or others, implemented as an extension
of wired local area networks and may be able to provide the last
few meters of connectivity between a wired network and mobile or
fixed devices. As shown in FIG. 1, the non-cellular network 130,
which is illustrated as a WLAN for example, is established by an
Access Point (AP) 131 which may connect to a local area network by
an Ethernet cable. The AP 131 typically receives, buffers, and
transmits data between the WLAN and the wired network
infrastructure. The AP 131 may have, on average, a coverage varying
from 20 meters in an area with obstacles (walls, stairways,
elevators etc) to 100 meters in an area with clear line of sight.
Note that, in the following description, the WLAN is only given as
an example, and the invention is not limited thereto.
Alternatively, the non-cellular network 130 may be a BT PAN, ZigBee
WPAN, or others.
[0027] The mobile communication device 110 may also be referred to
as a Mobile Station (MS), Mobile Terminal (MT), or User Equipment
(UE). For example, the mobile communication device 110 may be a
mobile phone (also known as a cellular or cell phone), a smart
phone, a laptop computer with wireless communications capability,
or others. The mobile communication device 110 may comprise two
wireless modules (not shown) for performing the functionality of
wireless transceiving to and from the cellular network 120 and the
non-cellular network 130. To further clarify, each wireless module
may comprise a Baseband unit (not shown) and a Radio Frequency (RF)
unit (not shown). The Baseband unit may contain multiple hardware
devices to perform baseband signal processing, including analog to
digital conversion (ADC)/digital to analog conversion (DAC), gain
adjusting, modulation/demodulation, encoding/decoding, and so on.
The RF unit may receive RF wireless signals, convert the received
RF wireless signals to baseband signals, which are processed by the
Baseband unit, or receive baseband signals from the Baseband unit
and convert the received baseband signals to RF wireless signals,
which are later transmitted. The RF unit may also contain multiple
hardware devices to perform radio frequency conversion. For
example, the RF unit may comprise a mixer to multiply the baseband
signals with a carrier oscillated in the radio frequency of the
wireless communications system, wherein the radio frequency may be
2.4 GHz utilized in WiFi systems, or 900 MHz, 1900 MHz, or 2100 MHz
utilized in WCDMA systems, or may be 900 MHz, 2100 MHz, or 2.6 GHz
utilized in LTE systems, or others depending on the RAT in use.
Also, the mobile communication device 110 may comprise a controller
module (not shown) for controlling the operation of the two
wireless modules and other functional components, such as a display
unit and/or keypad serving as a Man-Machine Interface (MMI), a
storage unit storing the program codes of applications, or others.
Alternatively, the two wireless modules may negotiate with each
other for coordinating the respective operations thereof, without
any mediator, e.g., the controller module.
[0028] FIG. 2 is a block diagram illustrating an exemplary software
architecture of the mobile communication device 110 according to an
embodiment of the invention. In the exemplary software
architecture, two protocol stack handlers 10 and 20, each of which
may be implemented as program code, when loaded and executed by a
processing unit or Micro-Processing Unit (MCU) (e.g., an MCU of a
Baseband unit) with a plurality of processing logic units, are
configured to communicate with the cellular network 120 and the
non-cellular network 130, respectively, in compliance with a
respective wireless communication protocol. Also, the exemplary
software architecture includes an mediator 30 which may be
implemented as program code and when loaded and executed by a
processing unit or MCU with a plurality of processing logic units,
is configured to control/coordinate the operations of the protocol
stack handler 10 and 20 to practice the smart handover method of
the invention. Alternatively, in another embodiment as shown in
FIG. 3, the protocol stack handler 10 and 20 may directly negotiate
with each other for coordinating the respective operations thereof
to practice the smart handover method of the invention, without the
mediator 30.
[0029] Specifically, the mobile communication device 110 is capable
of performing smart handovers between the cellular network 120 and
the non-cellular network 130 for obtaining wireless services with
fair transceiving rates. FIG. 4 is a state transition diagram
illustrating state machine operations of the mobile communication
device 110 according to an embodiment of the invention. The
"Cellular-connected" state represents a state where the mobile
communication device 110 is connected to the cellular network 120
for obtaining wireless services, while the "WiFi-associated" state
represents a state where the mobile communication device 110 is
connected to the non-cellular network 130 for obtaining wireless
services. For the case where the mobile communication device 110 is
in the "Cellular-connected" state, if a new AP is detected with a
signal quality greater than a threshold value, the mobile
communication device 110 may disconnect with the cellular network
120 and connect to the non-cellular network 130 via the new AP, and
then enter the "WiFi-associated" state. In one embodiment, the
signal quality of the AP may be determined by measuring the
Received Signal Strength Indicator (RSSI) of the signals from the
AP. Note that, other measuring indicators, such as Signal to Noise
Ratio (SNR), Interference to Signal Ratio (ISR), Packet Error Rate
(PER), and Bit Error Rate (BER), etc., may be employed for
determining the signal quality of an AP, and the invention is not
limited thereto. In another situation, if the signal quality of a
previously detected AP increases so that the currently detected
signal quality is greater than the sum of the previously detected
signal quality and a margin value, the mobile communication device
110 may disconnect with the cellular network 120 and connect to the
non-cellular network 130 via the AP, and then enter the
"WiFi-associated" state. To further clarify, the margin value may
be a predetermined buffer to eliminate the ping-pong effect as
shown in FIG. 5. Particularly, the ping-pong effect occurs when the
coverage of the cellular network 120 and the non-cellular network
130 overlap and the mobile communication device 110 wanders near
the coverage edge of the non-cellular network 130. Around the
coverage edge, the signal quality of the non-cellular network 130
may be weak and unstable, and without the margin value, handovers
back and forth between the cellular network 120 and the
non-cellular network 130 may be too frequent, thus consuming
unnecessary power. Thus, by configuring a proper margin value,
frequent handovers between the cellular network 120 and the
non-cellular network 130 may be avoided. For the case where the
mobile communication device 110 is in the "WiFi-associated" state,
if the transceiving rate (referred to herein as "speed" for
brevity) of the link to the currently associated AP is lower than
the speed of the link to the cellular network 120, the mobile
communication device 110 may disconnect with the non-cellular
network 130 and connect to the cellular network 120, and then enter
the "Cellular-connected" state. To be more specific, the speed of
the link to the currently associated AP may be determined according
to the transceiving status between the mobile communication device
110 and the associated AP, and the speed of the link to the
cellular network 120 may be determined according to the system
information broadcasted by the cellular network 120. In another
embodiment, the mobile communication device 110 may transit from
the "WiFi-associated" state to the "Cellular-connected" state if
the speed of the link to the currently associated AP is lower than
a predetermined value (e.g., 2 Mbps).
[0030] FIG. 6 is a flow chart illustrating a smart handover method
for handing over the mobile communication device 110 from the
cellular network 120 to the non-cellular network 130 according to
an embodiment of the invention. In this embodiment, the mobile
communication device 110 is initially connected to the cellular
network 120 and is in a "Cellular-connected" state. To begin, the
mobile communication device 110 periodically scans for any nearby
non-cellular network (step S610). If a non-cellular network is
detected, the mobile communication device 110 then determines
whether it was previously connected to the detected non-cellular
network (step S620). If so, the mobile communication device 110
further determines whether the currently detected signal quality of
the non-cellular network is greater than the sum of the previously
detected signal quality of the non-cellular network and a margin
value to eliminate the ping-pong effect (step S630). Specifically,
the mobile communication device 110 may distinguish a new
non-cellular network from a previously associated non-cellular
network by identifying the Media Access Control (MAC) addresses
and/or Service Set Identifiers (SSIDs) of all detected non-cellular
networks. That is, if the MAC address or SSID of a detected
non-cellular network is not found in the connection history stored
in the mobile communication device 110, then the detected
non-cellular network is a new non-cellular network; otherwise, the
detected non-cellular network is a previously associated
non-cellular network. It is noted that, there may be a situation
where two or more non-cellular networks in an area are configured
with the same SSID, and in this case, the MAC address instead of
the SSIDs should be used to uniquely identify each one of the
non-cellular networks in the area. The previously detected signal
quality of the non-cellular network may be the signal quality of
the non-cellular network at the time when the mobile communication
device 110 decided to perform handover from the non-cellular
network to the cellular network 120. If the currently detected
signal quality of the non-cellular network is greater than the sum
of the previously detected signal quality of the non-cellular
network and a margin value to eliminate the ping-pong effect, the
mobile communication device 110 conducts handover to the
non-cellular network. Specifically, the mobile communication device
110 first tries to establish a connection to the non-cellular
network (step S640), and then waits for acceptance of the
connection from the non-cellular network (step S650). If the
connection is accepted by the non-cellular network, the mobile
communication device 110 then disconnects with the cellular network
120 (step S660) and enters the "WiFi-associated" state; otherwise,
if the connection is rejected by the non-cellular network, the
mobile communication device 110 stays in the "Cellular-connected"
state. Subsequent to step S620, if not, i.e., the detected
non-cellular network is a new non-cellular network which the MS has
never connected to previously, the mobile communication device 110
determines whether the signal quality of the new non-cellular
network is greater than a threshold value (step S670). If so, the
flow proceeds to step S640, and if not, the flow goes back to the
initial state.
[0031] It is noted that, before performing the smart handover
method of FIG. 6, the mobile communication device 110 may first
perform a 2-stage monitoring of the signal quality of any nearby
non-cellular network, as shown in FIG. 7. In the first stage, the
mobile communication device 110 may periodically detect the signal
quality of any nearby non-cellular network during every N seconds,
wherein N may be configured to be 6, 15, or any other number,
depending on the power-saving settings of the mobile communication
device 110. Once the signal quality of a non-cellular network is
detected to be greater than a first threshold X1, then the mobile
communication device 110 proceeds to the second stage where it
continues to monitor the signal quality of the detected
non-cellular network and detect its moving direction in relation to
the detected non-cellular network. When the signal quality of the
detected non-cellular network is greater than a second threshold X2
and it is detected that the mobile communication device 110 is
moving towards the AP of the detected non-cellular network, the
mobile communication device 110 may perform the smart handover
method of FIG. 5, wherein the second threshold X2 is greater than
the first threshold X1. Specifically, the moving direction of the
mobile communication device 110 may be determined by calculating
the moving average of the monitored signal quality of the
non-cellular network. FIG. 8A is a schematic diagram illustrating
RSSI changes for inward movement towards a non-cellular network
according to an embodiment of the invention. As shown in FIG. 8A,
the RSSIs of the detected non-cellular network monitored at time
t1, t2, t3, t4, and t5 are -91 dBm, -88 dBm, -86 dBm, -90 dBm, -84
dBm, respectively, wherein the RSSI monitored at time t4 may be
discarded as noise. The moving average of the mobile communication
device 110 may be determined by calculating the slope of the
monitored RSSIs. Since the slope of the monitored RSSIs is
positive, it is determined that the mobile communication device 110
is moving towards the AP of the detected non-cellular network. FIG.
8B is a schematic diagram illustrating RSSI changes for outward
movement from a non-cellular network according to an embodiment of
the invention. As shown in FIG. 8B, the RSSIs of the detected
non-cellular network monitored at time t1, t2, t3, t4, and t5 are
-91 dBm, -88 dBm, -86 dBm, -88 dBm, -90 dBm, respectively, wherein
the RSSI monitored at time t3 may be considered as a turning point
with respect to the moving direction of the mobile communication
device 110. The moving average of the mobile communication device
110 may be determined by calculating the slope of the monitored
RSSIs. Since the slope of the monitored RSSIs is negative, it is
determined that the mobile communication device 110 is moving away
from the AP of the detected non-cellular network. In another
embodiment, the Simple Moving Average (SMA) formula may be employed
for determining the moving direction of the mobile communication
device 110, and the invention is not limited thereto. Note that the
detailed descriptions concerning the calculation of the SMA are
omitted herein as they are beyond the scope of the invention.
[0032] FIG. 9 is a flow chart illustrating a smart handover method
for handing over the mobile communication device 110 from the
non-cellular network 130 to the cellular network 120 according to
an embodiment of the invention. In this embodiment, the mobile
communication device 110 is initially connected to the non-cellular
network 130 and is in a "WiFi-associated" state. To begin, the
mobile communication device 110 periodically determines whether the
speed of the link to the AP 131 is lower than 2 Mbps and whether
the signal quality of the non-cellular network 130 is lower than a
threshold T (step S910). Specifically, the speed of the link to the
AP 131 may be determined according to the transceiving status
between the mobile communication device 110 and the AP 131, and the
threshold T is used to eliminate the situation where the mobile
communication device 110 may be moving at a high speed away from
the AP 131 and used to eliminate the situation where the detected
speed of the link to the AP 131 may not be accurate for real-time
changes. For example, the speed of the link to the AP 131 detected
at time t1 is greater than 2 Mbps and the next periodic detection
is 6 seconds thereafter. In this example, the mobile communication
device 110 moves rapidly away from the AP 131 to a place where the
signal quality of the non-cellular network 130 drops sharply in
less than 6 seconds. Note that the speed of the link to the AP 131
detected at time t1 is not accurate enough to be taken as the only
measuring factor. Accordingly, the threshold T is used. The value
of the threshold T may be predetermined to be a specific number
according to any one or more considerations, such as the coverage
of the non-cellular network 130, the geological environment of the
non-cellular network 130, etc. Note that, the lower bound for the
speed of the link to the AP 131 may be configured to any value
other than 2 Mbps, and the invention is not limited thereto.
[0033] Subsequent to step S910, if so, the mobile communication
device 110 further determines whether a link to the cellular
network 120 is available and whether the speed of the link to the
cellular network 120 is greater than the speed of a GPRS link (step
S920). Specifically, the mobile communication device 110 may first
perform an attachment procedure to register to the cellular network
130, and a link to the cellular network 120 is available if the
registration is successful. The speed of the link to the cellular
network 120 may be determined according to the system information
broadcasted by the cellular network 120, and in general, the speed
of a GPRS link is up to 80 Kbps for downlink and 20Kbps for uplink
with Coding Scheme 4 (CS-4). In another embodiment, if the type of
wireless service in use requires a higher data rate, the mobile
communication device 110 may instead determine, in step S920,
whether the speed of the link to the cellular network 120 is
greater than (or equal to) the speed of a WCDMA link, an HSPA link,
or an LTE link.
[0034] If a link to the cellular network 120 is available and the
speed of the link is greater than the speed of a GPRS link, then
the mobile communication device 110 conducts handover from the
non-cellular network 130 to the cellular network 120 (step S930),
and then disconnects with the non-cellular network 130 and enters
the "Cellular-connected" state. In another embodiment, before step
S930, the mobile communication device 110 may prompt the user to
confirm whether to proceed to perform handover from the
non-cellular network 130 to the cellular network 120, and only
proceed to step S930 when the user confirms the decision.
Subsequent to steps S910 and S920, if not, the mobile communication
device 110 stays in the "WiFi-associated" state and waits for the
next periodic check on the speed of the link to the AP 131.
[0035] It is noted that, before performing the smart handover
method of FIG. 9, the mobile communication device 110 may first
perform a 2-stage monitoring of the signal quality of any nearby
non-cellular network, as shown in FIG. 10. In the first stage, the
mobile communication device 110 may periodically detect the signal
quality of the non-cellular network 130 in every N seconds, wherein
N may be configured to be 6, 15, or any other number, depending on
the power-saving settings of the mobile communication device 110.
If once the signal quality of the non-cellular network 130 is
detected to be lower than a first threshold Y1, then the mobile
communication device 110 proceeds to the second stage where it
continues to monitor the signal quality of the non-cellular network
130 and detect its moving direction against the non-cellular
network 130. When the signal quality of the non-cellular network
130 is lower than a second threshold Y2 and it is detected that the
mobile communication device 110 is moving away from the AP 131, the
mobile communication device 110 may perform the smart handover
method of FIG. 9, wherein the first threshold Y1 is greater than
the second threshold Y2. Specifically, the moving direction of the
mobile communication device 110 may be determined by calculating
the moving average of the monitored signal quality of the
non-cellular network 130. For the calculation of the moving
average, reference may be made to the related descriptions of FIGS.
8A and 8B.
[0036] While the invention has been described by way of example and
in terms of preferred embodiment, it is to be understood that the
invention is not limited thereto. Those who are skilled in this
technology can still make various alterations and modifications
without departing from the scope and spirit of this invention.
[0037] Use of ordinal terms such as "first", "second", "third",
etc., in the claims to modify a claim element does not by itself
connote any priority, precedence, or order of one claim element
over another or the temporal order in which acts of a method are
performed, but are used merely as labels to distinguish one claim
element having a certain name from another element having a same
name (but for use of the ordinal term) to distinguish the claim
elements.
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