U.S. patent application number 12/556423 was filed with the patent office on 2010-01-07 for method and system for wireless channel selection by a mobile device.
This patent application is currently assigned to RESEARCH IN MOTION LIMITED. Invention is credited to ADRIAN BUCKLEY, CRAIG DUNK, VYTAUTAS ROBERTAS KEZYS, RUSSELL OWEN.
Application Number | 20100003988 12/556423 |
Document ID | / |
Family ID | 34887279 |
Filed Date | 2010-01-07 |
United States Patent
Application |
20100003988 |
Kind Code |
A1 |
BUCKLEY; ADRIAN ; et
al. |
January 7, 2010 |
METHOD AND SYSTEM FOR WIRELESS CHANNEL SELECTION BY A MOBILE
DEVICE
Abstract
A method and mobile device for performing wireless channel
selection that employs more than one concurrent level 2 interface
to facilitate a level 3 handoff. The method and device maintain an
active service over a first level 3 connection through a first
transceiver, establish a second level 3 connection through a second
transceiver, and then switch the service over to the second
connection. To establish an appropriate level 3 connection, the
mobile device may evaluate candidate channels against criteria
associated with the active service to ensure quality of service can
be maintained over the new connection or may adapt the active
service to a candidate channel.
Inventors: |
BUCKLEY; ADRIAN; (TRACY,
CA) ; DUNK; CRAIG; (GUELPH, CA) ; KEZYS;
VYTAUTAS ROBERTAS; (HAMILTON, CA) ; OWEN;
RUSSELL; (WATERLOO, CA) |
Correspondence
Address: |
DOCKET CLERK;Kelly-Krause
PO BOX 12608
DALLAS
TX
75225
US
|
Assignee: |
RESEARCH IN MOTION LIMITED
WATERLOO
CA
|
Family ID: |
34887279 |
Appl. No.: |
12/556423 |
Filed: |
September 9, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10789435 |
Feb 27, 2004 |
7596119 |
|
|
12556423 |
|
|
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|
Current U.S.
Class: |
455/436 |
Current CPC
Class: |
H04B 7/022 20130101;
H04W 36/0022 20130101; H04W 36/12 20130101 |
Class at
Publication: |
455/436 |
International
Class: |
H04W 36/00 20090101
H04W036/00 |
Claims
1. A method of wireless channel selection by a mobile device having
first and second transceivers, the mobile device communicating with
a wireless network, comprising: creating a first connection with
the wireless network over a first channel using a first
transceiver; establishing a service between the mobile device and a
remote point over said first connection; selecting a second channel
and tuning the second transceiver to the second channel; requesting
resources over the second channel, including requesting a second
connection with the wireless network; determining whether granted
resources are adequate for supporting said service; switching said
service to said second connection; and terminating said first
connection.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of U.S. patent
application Ser. No. 10/789,435, filed on Feb. 27, 2004, the entire
disclosure of which is incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The present invention relates to wireless mobile devices
and, in particular, to a method and system for wireless channel
selection by a mobile device.
BACKGROUND OF THE INVENTION
[0003] Many of the mobile devices available today provide complex
functionality far beyond simple voice communications. For example,
many devices enable a user to access remote servers or sites over a
public network, like the Internet. Some of these devices permit
users to engage in Voice-over-IP (VoIP) telephone calls. Other
devices allow users to receive streaming data from remote
resources, such as streaming video or audio data.
[0004] This greater level of functionality, especially the receipt
of real-time streamed data, presents particular quality of service
issues. For example, the mobile device must ensure that the
streamed data--such as a VoIP call--is maintained during roaming.
Accordingly, when roaming within a network from one base station or
cell to another base station or cell, the network must provide for
certain latency in the communications to ensure that there is
sufficient time to negotiate a handoff of the call between base
stations without introducing noticeable delay into the streamed
data.
[0005] A particular difficulty arises when the device roams from
one network to another network of a different type. For example,
the mobile device may initiate and establish a call within a
General Packet Radio System (GPRS) network and may subsequently
move geographically into an area served by a wireless local area
network (WLAN) or IEEE802.11 coverage. Existing mobile devices may
not be able to maintain the service being conducted over the call
when the device switches the call to the new network.
SUMMARY OF THE INVENTION
[0006] The present invention provides a method and mobile device
for performing wireless channel selection that employs more than
one concurrent level 2 interface to facilitate a level 3 handoff.
The method and device maintain an active service over a first level
3 connection through a first transceiver, establish a second level
3 connection through a second transceiver, and then switch the
service over to the second connection. To establish an appropriate
level 3 connection, the mobile device may evaluate candidate
channels against criteria associated with the active service to
ensure quality of service can be maintained over the new
connection. In some embodiments, the active service may be adapted
to operate over a candidate channel having different
characteristics from the existing channel.
[0007] In one aspect, the present invention provides a method of
wireless channel selection by a mobile device, the mobile device
communicating with a wireless network. The method includes steps of
creating a first connection with the wireless network over a first
channel; establishing a service between the mobile device and a
remote point over the first connection; creating a second
connection with the wireless network over a second channel;
switching the service to the second connection; and terminating the
first connection.
[0008] In another aspect the present invention provides a mobile
device for wireless channel selection, the mobile device
communicating with a wireless network. The mobile device includes a
first transceiver for creating a first connection with the wireless
network over a first channel; a second transceiver for creating a
second connection with the wireless network over a second channel;
and a switching module coupled to the first and second transceivers
and directing the first transceiver to create the first connection,
establishing a service between the mobile device and a remote point
over the first connection, selecting the second channel, and
directing the second transceiver to create the second connection;
wherein, upon creation of the second connection, the switching
module switches the service from the first connection to the second
connection.
[0009] In a further aspect, the present invention provides a method
of wireless channel selection by a mobile device, the mobile device
communicating with a wireless network, and having a first
connection with the wireless network over a first channel, the
first connection supporting an active service between the mobile
device and a remote point. The method includes the steps of
selecting a second channel from a set of candidate channels based
upon characteristics of the candidate channels and service criteria
associated with the active service; creating a second connection
with the wireless network over the second channel; switching the
active service to the second connection; and terminating the first
connection.
[0010] In yet another aspect, the present invention provides a
mobile device for wireless channel selection, the mobile device
communicating with a wireless network. The mobile device includes a
first transceiver for creating a first connection with the wireless
network over a first channel; a second transceiver for creating a
second connection with the wireless network over a second channel;
a memory for storing characteristics for at least one candidate
channel and storing service criteria for an active service between
the mobile device and a remote point; and a switching module
coupled to the first and second transceivers and to the memory, the
switching module selecting the second channel based upon an
evaluation of the characteristics of the at least one candidate
channel against the service criteria, and wherein the switching
module switches the service from the first connection to the second
connection.
[0011] Other aspects and features of the present invention will be
apparent to those of ordinary skill in the art from a review of the
following detailed description when considered in conjunction with
the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] Reference will now be made, by way of example, to the
accompanying drawings which show an embodiment of the present
invention, and in which:
[0013] FIG. 1 shows a block diagram of an embodiment of a mobile
device and a wireless communication network;
[0014] FIG. 2 which shows the block diagram of FIG. 1 in a roaming
context;
[0015] FIG. 3 shows a block diagram of an embodiment of the mobile
device;
[0016] FIG. 4 shows a block diagram of an embodiment of a
communication subsystem for the mobile device of FIG. 3;
[0017] FIG. 5 shows, in flowchart form, a method of wireless
channel selection by a mobile device; and
[0018] FIG. 6 shows, in flowchart form, a method of selecting a new
candidate channel and switching a service to the new channel.
[0019] Similar reference numerals are used in different figures to
denote similar components.
DESCRIPTION OF SPECIFIC EMBODIMENTS
[0020] The following description of one or more specific
embodiments of the invention does not limit the implementation of
the invention to any particular computer programming language or
system architecture. The present invention is not limited to any
particular operating system, mobile device architecture, or
computer programming language.
[0021] The following description makes reference to choosing a
channel or operating a service over a channel. It will be
understood that the term channel and the notion of selecting a
channel is meant to encompass the selection of a channel from among
different frequencies and/or channels.
[0022] Reference is first made to FIG. 1, which shows a mobile
device 10 and a wireless communication network 50. The wireless
communication network 50 includes a first base station 80 and a
second base station 82 coupled to a core network 84. The core
network 84 may include a collection of interconnected networks of
different types. For example, the core network 84 may include a
GPRS network coupled to a WLAN and to the Internet. It will be
appreciated by those of ordinary skill in the art that the core
network 84 may include a variety of other interconnected
networks.
[0023] The mobile device 10 includes a first transceiver 14 and a
second transceiver 16. The mobile device 10 is capable of
establishing communications with the wireless communication network
50. For example, the first transceiver 14 may have a first link 90
with the first base station 80 and the second transceiver 16 may
have a second link 92 with the second base station 82.
[0024] Under normal operations, the mobile device 10 employs one of
the transceivers 14, 16 to establish and maintain a link with a
base station 80, 82. This link is used to maintain a communication
service, such as, for example, a voice call. Accordingly, the
mobile device 10 establishes a level 2 (L2) connection to the
wireless communication network 50 over the link 90 or 92 and then
establishes a level 3 (L3) connection with an administrative domain
to create the communication service. For example, the first
transceiver 14 may have an active service over the first link 90 to
the first base station 80, such as a VoIP session. This service
operates over an L3 connection between the mobile device 10 and a
remote location within the wireless communication network 50 using
the first link 90.
[0025] The mobile device 10 may determine that it has moved into an
area better served by another base station, in which case it will
attempt to locate an alternative link to another base station. The
mobile device 10 may make this decision as a result of signal
strength monitoring according to the appropriate standard, as will
be understood by those of ordinary skill in the art. The mobile
device 10 may locate an available channel on the second base
station 82 by scanning or through broadcast information received
from the first base station 80. Once the mobile device 10 has
located an alternative channel, the mobile device 10 tunes to that
new channel and obtains broadcast information from the second base
station 82. There may be multiple candidate channels.
[0026] Based on the broadcast information regarding the new
channel, the mobile device 10 determines if the channel is
available. The mobile device 10 also evaluates the characteristics
of the channel against the type of service currently operating on
the mobile device. The type of service may dictate that certain
minimum channel characteristics are required from any candidate
channel in order to maintain the service. For example, the type of
service may be a high bandwidth service. In this case, a low
bandwidth channel would be inappropriate. Other factors including
cost and reachability may also factor into the decision.
Reachability refers to the ability to reach the same entity within
the wireless communication network 50 that is providing the active
service.
[0027] Once the new channel is approved by the mobile device 10,
the mobile device 10 requests resources from the wireless
communications network 50. In other words, the mobile device 10
requests L2 and L3 connectivity. If resources are granted
establishing a second link 92, then the mobile device 10 assesses
whether the granted resources are sufficient to operate the
service. If the resources are sufficient, then the existing service
being operated over the first link 90 is switched to the second
link 92.
[0028] In another embodiment, the second link 92 has
characteristics different from the first link 90, such as a lower
bandwidth or longer mean latency. The mobile device 10 may adapt
the service to operate over the second link 92. In other words, the
service is modified based upon the characteristics of the new
channel. The adaptation may include changing the codec(s) used with
regard to the service. For example, a service that involves audio
and/or video may be modified to consume less bandwidth by modifying
the codec used for the audio and/or the video, or by dropping the
video and transmitting the audio only. It will be understood that
other modification could be made to the service to ensure it
operates successfully over a new channel having different
characteristics.
[0029] Reference is made to FIG. 2, which shows the block diagram
of FIG. 1 in a roaming context. The core network 84 includes an
anchor point 98. The anchor point 98 may be a router, server, or
other node within the wireless communication network 50.
[0030] The anchor point 98 is coupled to one or more servers 100,
102, 104 that support a communication service. In another
embodiment, the anchor point 98 is one of the servers 100, 102, or
104 providing a communication service. The communication service is
represented by a first data stream 94 over the first link 90 to the
anchor point 98. The anchor point 98 processes the first data
stream 94 and transmits it to one or more of the servers 100, 102,
104.
[0031] When the mobile device 10 requests network resources to
establish the second link 92, it seeks to establish a connection to
the anchor point 98. In order to create the second link 92 and
establish an L3 connection to support the transfer of the
communication service, the mobile device 10 may require the
allocation of an IP address to facilitate communication of packets
from the anchor point 98 to the mobile device 10 over the second
link 92. The request for resources may also incorporate
authentication steps, authorization steps, and ensuring that there
is sufficient bandwidth and that the level of latency is
acceptable.
[0032] If these resources are granted, and if the mobile device 10
determines that the resources are adequate for supporting the
existing communication service, then a second data stream 96 is
established to support the communication service.
[0033] Accordingly, by establishing overlapping L2 connectivity,
the mobile device 10 is able to select and obtain resources over a
new channel and move a service over to the new channel without
losing L3 connectivity. This minimizes latency in the handoff.
[0034] Reference is now made to FIG. 3, which shows a block diagram
of the mobile device 10 in an example embodiment. In this
embodiment, the mobile device 10 has data and possibly also voice
communication capabilities. In an example embodiment, the mobile
device 10 has the capability to communicate with other computer
systems on the Internet. Depending on the functionality provided by
the device, in various embodiments the device may be a data
communication device, a multiple-mode communication device
configured for both data and voice communication, a mobile
telephone, a PDA (personal digital assistant) enabled for wireless
communication, or a computer system with a wireless modem, among
other things.
[0035] In this embodiment, the mobile device 10 includes a
communication subsystem 12, including a first transceiver 14, a
second transceiver 16, and associated components such as a
processor 20, which in one embodiment includes a digital signal
processor (DSP). In some embodiments, the communication subsystem
includes local oscillator(s) (LO) (not shown), and in some
embodiments the communication subsystem 12 and a microprocessor 38
share an oscillator. As will be apparent to those skilled in the
field of communications, the particular design of the communication
subsystem 12 will be dependent upon the communication network in
which the device is intended to operate. The transceivers 14, 16
may have separate antennae or may share an antenna.
[0036] Signals received by the antenna through the wireless
communication network 50 are input to one of the transceivers 14 or
16, which may perform such common transceiver functions as signal
amplification, frequency down conversion, filtering, and the like.
In a similar manner, signals to be transmitted are processed,
including modulation and encoding for example, by the processor 20
and input to one of the transceivers 14 or 16 for frequency up
conversion, filtering, amplification and transmission over the
wireless communication network 50.
[0037] The device 10 includes the microprocessor 38 that controls
the overall operation of the device. The microprocessor 38
interacts with communications subsystem 12 and also interacts with
further device subsystems such as the display 22, flash memory 24,
random access memory (RAM) 26, auxiliary input/output (I/O)
subsystems 28, serial port 30, keyboard or keypad 32, speaker 34,
microphone 36, a short-range communications subsystem 40, and any
other device subsystems generally designated as 42.
[0038] Some of the subsystems shown in FIG. 1 perform
communication-related functions, whereas other subsystems may
provide "resident" or on-device functions. Notably, some
subsystems, such as keyboard 32 and display 22 for example, may be
used for both communication-related functions, such as entering a
text message for transmission over a communication network, and
device-resident functions such as a calculator or task list.
[0039] Operating system software 54 and various software
applications 58 used by the microprocessor 38 are, in one example
embodiment, stored in a persistent store such as flash memory 24 or
similar storage element. Those skilled in the art will appreciate
that the operating system 54, software applications 58, or parts
thereof, may be temporarily loaded into a volatile store such as
RAM 26. It is contemplated that received communication signals may
also be stored to RAM 26.
[0040] The microprocessor 38, in addition to its operating system
functions, preferably enables execution of software applications 58
on the device. A predetermined set of software applications 58
which control basic device operations, including at least data and
voice communication applications for example, will normally be
installed on the device 10 during manufacture. Further software
applications 58 may also be loaded onto the device 10 through the
wireless communication network 50, an auxiliary I/O subsystem 28,
serial port 30, short-range communications subsystem 40 or any
other suitable subsystem 42, and installed by a user in the RAM 26
or a non-volatile store for execution by the microprocessor 38.
Such flexibility in application installation increases the
functionality of the device and may provide enhanced on-device
functions, communication-related functions, or both. For example,
secure communication applications may enable electronic commerce
functions and other such financial transactions to be performed
using the device 10.
[0041] In a data communication mode, a received signal such as a
text message or web page download will be processed by the
communication subsystem 12 and input to the microprocessor 38,
which will preferably further process the received signal for
output to the display 22, or alternatively to an auxiliary I/O
device 28. A user of device 10 may also compose data items within a
software application 58, such as email messages for example, using
the keyboard 32 in conjunction with the display 22 and possibly an
auxiliary I/O device 28. Such composed items may then be
transmitted over a communication network through the communication
subsystem 12.
[0042] The serial port 30 in FIG. 1 would normally be implemented
in a personal digital assistant (PDA)-type communication device for
which synchronization with a user's desktop computer (not shown)
may be desirable, but is an optional device component. Such a port
30 would enable a user to set preferences through an external
device or software application and would extend the capabilities of
the device by providing for information or software downloads to
the device 10 other than through the wireless communication network
50.
[0043] A short-range communications subsystem 40 is a further
component which may provide for communication between the device 10
and different systems or devices, which need not necessarily be
similar devices. For example, the subsystem 40 may include an
infrared device and associated circuits and components or a
Bluetooth.TM. communication module to provide for communication
with similarly enabled systems and devices. The device 10 may be a
handheld device.
[0044] Wireless communication network 50 is, in an example
embodiment, a wireless packet data network, (e.g. Mobitex.TM. or
DataTAC.TM.), which provides radio coverage to mobile devices 10.
Wireless communication network 50 may also be a voice and data
network such as GSM (Global System for Mobile Communication), GPRS,
CDMA (Code Division Multiple Access), or various other third
generation networks such as EDGE (Enhanced Data rates for GSM
Evolution) or UMTS (Universal Mobile Telecommunications
Systems).
[0045] Reference is now made to FIG. 4, which shows a block diagram
of an embodiment of the communication subsystem 12. In addition to
the first transceiver 14 and the second transceiver 16, the
communications subsystem 12 includes a switching manager 70, a
radio network database (RND) 72, and a user data database (UDD) 74.
The first and second transceivers 14, 16 each include a transmit
module 60, 63, a receive module 62, 65, and a radio resource
sub-layer manager (RRM) 61, 64.
[0046] The switching manager 70 manages the connections between the
mobile device 10 (FIG. 1) and the wireless communication network 50
(FIG. 1). The switching manager 70 requests dedicated resources for
establishing data transfer and for coordinating information
received on one or both of the transceivers 14, 16. It alerts one
of the transceivers 14 or 16 when it is necessary to search for a
new channel. The switching manager 70 also directs whether the
source data 76 should go to the first or second transceiver 14, 16
for transmission. It may also perform mobility management
functions, such as authentication.
[0047] The radio network database 72 stores information about the
candidate channels that have been located and any broadcast
information located. It may also store signal strength information.
Accordingly, the radio network database 72 maintains up-to-date
records of the potential channels and their characteristics.
[0048] The user data database 74 stores information regarding the
attributes to be used in selecting a channel. These attributes may
include signal strength, minimum bandwidth, mean bandwidth, minimum
latency, mean latency, maximum latency, security settings,
technology types, and other attributes.
[0049] Each radio resource sub-layer manager (RRM) 61, 64 is
responsible for radio link control and medium access control
(RLC/MAC). The RRMs 61, 64 instruct the receiver modules 63, 65 to
scan the appropriate frequency bands. When a compatible channel is
located, the RRM 61, 64 locates its broadcast information. If the
broadcast information advertises any neighbour channels, then the
RRM 61, 64 instructs the receiver module 63, 65 to tune to those
channels as well to obtain their signal strengths and broadcast
information. The RRM passes the information that it gathers from
the located channels on to the switching manager 70, which then
stores the information in the radio network database 72. The RRMs
61, 64 dynamically update the information in the radio network
database 72 as the signal strengths of located channels change.
[0050] It will be understood that the various parts of the
communication subsystem 12 shown in the block diagram of FIG. 4 may
be implemented by various other parts or subsystems shown in the
block diagram of FIG. 3. For example, the UDD 74 or the RND 72 may
be stored within flash memory 24 (FIG. 3) or within RAM 26 (FIG.
3). The switching manager 70 may be implemented through the
microprocessor 38 or through a dedicated purpose element, such as
the processor 20.
[0051] The switching manager 70 selects the channel to be used for
communications and sends control information to one of the
transceivers 14, 16 instructing it to tune to the selected channel.
The switching manager 70 also sends (via one of the transceivers
14,16) a request for resources. Once resources are granted, the
switching manager 70 directs that the source data 76 should go to
the tuned transceiver 14 or 16.
[0052] Reference is now made to FIG. 5 in conjunction with FIG. 4.
FIG. 5 shows, in flowchart form, a method 200 for wireless channel
selection in accordance with the present invention. The method 200
begins in step 202, wherein the switching manager 70 selects one of
the available channels and instructs the first transceiver 14 to
tune to the selected channel. The switching manager 70 then sends a
request for resources to the wireless communication network 50 in
step 204 using the first transceiver 14. If the wireless
communication network 50 grants the resources, then in step 206 the
source data 76 is directed to the first transceiver 14 for
transmission.
[0053] While a communication service, such as a VoIP call or other
service, is established using the link set-up over the selected
channel using the first transceiver 14, the second transceiver 16
is scanning the environment for alternative channels in step 208.
The second transceiver 16 may scan any of the channels that were
originally located by the first transceiver 14 or it may locate
additional or new channels. It provides updated channel information
to the switching manager 70 for storage in the radio network
database 72. If the second transceiver 72 notes that previously
located channels have become unavailable, due to loss of signal
strength or loss of availability, then it will notify the switching
manager 70 and the information in the radio network database 72 is
updated accordingly. Those channels that become unavailable are
marked as such and are later dropped altogether from the radio
network database 72 if they are not relocated within a reasonable
period of time.
[0054] While the second transceiver 16 scans available channels and
the radio network database 72 is updated, the first transceiver 14
conducts signal strength monitoring on the selected channel over
which the service is operating. If, in step 210, the first
transceiver 14 detects that the signal strength has dropped below a
threshold defined by the appropriate standard, then the method 200
proceeds to step 212 to select a new channel.
[0055] In steps 212, 213 and 214, the switching manager 70 selects
a new candidate channel and instructs the second transceiver 16 to
tune to the new channel. Once the second transceiver 16 has located
the new channel it informs the switching manager 70 and the
switching manager 70 sends a request for resources from the
wireless communication network 50 (FIG. 1). Obtaining resources
includes obtaining the necessary bearer channel, which includes
establishing a level 3 network connection with the anchor point 98
(FIG. 2). The anchor point 98 is a point in the core network 84
(FIG. 2) that is already processing the first data stream 94 (FIG.
2) for the service operating over the first link 90 (FIG. 2). The
anchor point 98 may be the server providing the service or may be
an intermediate point in the core network 84. Establishing a level
3 network connection with the anchor point 98 may include
allocation of a new IP address to the mobile device that may differ
from the IP address used for the first link 90. Accordingly, if
resources are granted, then the mobile device 10 will have two
concurrent level 3 communication paths established with the
wireless communication network 50.
[0056] If resources are granted, then the switching manager 70
causes the source data 76 to be routed to the second transceiver 16
for transmission.
[0057] If resources are not granted, then the switching manager 70
selects a new candidate channel and repeats the attempt to obtain
resources.
[0058] The steps of selecting a new channel and switching a service
to that new channel shown in steps 212, 213 and 214 are shown in
greater detail in FIG. 6, which shows in flowchart form a method
300 of selecting a new candidate channel and switching a service to
the new channel.
[0059] The method 300 begins when the switching manager 70 (FIG. 4)
decides to select a new channel, such as for example in response to
a drop in signal strength on a channel currently in use. In step
302, the switching manager 70 reads selection criteria from the
user data database 74 (FIG. 4). The selection criteria reflect the
channel characteristics necessary to maintain a certain quality of
service based upon the type of service. The selection criteria may
include the type of service being operated on the mobile device 10
(i.e. VoIP, streaming video, simple e-mail, etc.), the bandwidth
requirements associated with the type of service (i.e. minimum
bandwidth requirements for maintaining certain quality of service
(QoS) standards), and any other channel characteristics associated
with the type of service. Other channel characteristics may include
latency associated with the link, security settings available, and
technology types (i.e. WLAN, GPRS, EDGE, W-CDMA, etc.).
[0060] In step 304, the switching manager 70 consults the radio
network database 72 (FIG. 4) to determine which candidate channels
are available. From among the candidate channels, the switching
manager 70 selects a first candidate in step 306. The selection may
be based upon a comparison of the characteristics of the channel
stored in the radio network database 72 and the channel
requirements provided by the user data database 74. Alternatively,
the candidate channels stored in the radio network database 72 may
be pre-filtered by the switching manager 70 against the channel
requirements during the regular updating of the radio network
database 72. In such an embodiment, the radio network database 72
would only contain candidate channels that appear to meet the
channel requirements. Therefore, the switching manager 70 may
select any one of the candidate channels. An appropriate algorithm
may be employed to select from among multiple candidate channels.
The algorithm may take into account bandwidth, signal strength, and
any other characteristic information regarding the candidate
channel.
[0061] Having selected a candidate channel, in step 308, the
switching manager 70 instructs the second transceiver to locate the
candidate channel and sends a request for resources to the wireless
network 50. If resources are refused then the switching manager 70
tries the next candidate channel. If resources are granted, then in
step 310 the switching manager 70 may compare the granted resources
against the channel requirements obtained in step 302 and may
accept or reject the candidate channel. If the channel is rejected,
then the switching manager 70 tries the next candidate channel.
[0062] If the resources granted are adequate, then in step 312 the
service is switched to the newly established connection over the
new candidate channel. Once the service has been switched to the
new channel using the second transceiver 16 (FIG. 1), the
connection using the first transceiver 14 (FIG. 1) is dropped and
the first transceiver 14 assumes the role of scanning for new
candidate channels and updating the radio network database 72. The
overlapping level 3 connectivity that results from the method 300
provides for a low latency handoff of the service.
[0063] In step 314, if the candidate channels have been exhausted
without finding an acceptable channel, then the handoff fails and
the service remains on the original channel.
[0064] In another embodiment, if the candidate channels and/or the
resources granted are insufficient to meet the service criteria,
then the switching manager 70 may direct that the service be
altered or adapted to function over the available channels. For
example, a service involving streaming video data may need to be
changed to streaming audio only or streaming video at a lower
resolution or refresh rate in order to function appropriately over
a narrower bandwidth connection.
[0065] The present invention may be embodied in other specific
forms without departing from the spirit or essential
characteristics thereof. Certain adaptations and modifications of
the invention will be obvious to those skilled in the art.
Therefore, the above discussed embodiments are considered to be
illustrative and not restrictive, the scope of the invention being
indicated by the appended claims rather than the foregoing
description, and all changes which come within the meaning and
range of equivalency of the claims are therefore intended to be
embraced therein.
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