Note: Descriptions are shown in the official language in which they were submitted.
CA 02474506 2004-07-23
WO 03/067918 PCT/US03/03625
1
METHOD AND APPARATUS FOR EFFICIENT SELECTION AND
ACQUISITION OF A WIRELESS COMMUNICATIONS SYSTEM
BACKGROUND OF THE INVENTION
Related Applications
[0001] This application claims priority to U.S. Provisional Patent Application
No.
60/355,742, filed on February 5, 2002.
Field of the Invention
[0002] The present invention relates generally to wireless communications and,
in
particular, to a method and apparatus for efficiently selecting and acquiring
a wireless
communications system. '
Description of the Related Art
[0003] A mobile device will often have access to more than one wireless
communications system in its geographic region. The quality of the wireless
services
available to the mobile device may vary from system to system depending on the
equipment used by each system, the features of the mobile device, the distance
between
the mobile device and local base stations, physical obstructions such as
buildings and
hills, and the volume of communications traffic on each system. The wireless
communications systems may also support different multiple-access wireless
communications protocols such as code division multiple access (CDMA),
wideband
CDMA (WCDMA), Advanced Mobile Phone Service (AMPS), Global System for
Mobile communications (GSM), General Packet Radio Services (GPRS) or High Data
Rate (HDR) technology (e.g., lxEV technology). In addition, the fees charged
to a user
of the mobile device may vary depending on the time of day, the duration of
the
connection with the wireless communications system and whether the mobile
device is
listed as a subscriber of the wireless communications system.
[0004] To assist with the selection of a desirable wireless communications
system,
conventional mobile devices store data describing known systems in a preferred
roaming list (PRL). The PRL typically includes a systems table which stores a
system
identifier (SID) and a network identifier (NID) for each known wireless
communications system, and an acquisition table which stores acquisition
parameters
CA 02474506 2004-07-23
WO 03/067918 PCT/US03/03625
2
including band, frequency and mode, for the known wireless communications
systems.
Within the systems table, the wireless communications systems are often
grouped by
geographic region and sorted from the most desirable to the least desirable
system in
each region. The most desirable system in a particular geographic region is
typically a
subscriber system, but may also be a roaming system that offers the mobile
device a
favorable combination of low cost and high quality of service. Roaming systems
offer
wireless services to non-subscriber mobile devices, usually at a much higher
fee than
subscription services, and may be desirable when the mobile device enters a
geographic
region that is outside the coverage area of the mobile device's subscription
service,
when the subscription services are blocked or otherwise unavailable, or when
the
subscription services are only available at an unacceptably low level of
quality.
[0005] During a mobile device's power-up sequence, attempts are made to
acquire and
register with the most desirable wireless communications system that is
available to the
mobile device in its current geographic region. In one approach, the mobile
device
identifies its current geographic region and then steps through the entries in
the systems
table, from the most desirable system in the identified geographic region to
the least
desirable system in the identified geographic region, until a system
acquisition and
registration attempt is successful. The mobile device may also attempt to
acquire and
register with a new wireless communications system during operation. For
example, the
connection between the mobile device and a current wireless communications
system
may be lost, requiring the acquisition of a new system by the mobile device.
In
addition, the wireless communications systems that are available to the mobile
device
may change as the position of the mobile device and its surrounding
environment
changes. To provide the user of the mobile device with the best combination of
high
quality and low cost, many mobile devices periodically attempt to acquire and
register
with a wireless communications system that is more desirable than the current
wireless
communications system used by the mobile device. The mobile device searches
the
systems table for wireless communications systems in its geographic region
that are
more desirable than the current system used by the mobile device and if more
desirable
systems are found in the systems table, the mobile device will switch away
from the
current communications channel and attempt to acquire and register with one of
the
more desirable systems.
[0006] A system acquisition sequence, such as the system acquisition sequences
described above, will often include a series of failed attempts to acquire a
signal and
CA 02474506 2004-07-23
WO 03/067918 PCT/US03/03625
3
register with the corresponding wireless communications system, followed by a
single
successful system acquisition and registration. A preferred roaming list
typically
includes over 50 systems and under certain conditions the mobile device may
spend
over 60 seconds stepping through the systems in the preferred roaming list
before an
acquisition attempt is successful. These failed acquisition attempts are
common and
may be caused by a variety of factors. For example, the mobile device may be
unable to
detect a pilot signal transmitted from a system base station if the pilot
signal is blocked
or weakened by physical obstructions, or if the mobile device is outside the
base
station's coverage area. Registration with the system may fail if the mobile
device and
the system use incompatible protocol revisions and hardware, or if system
otherwise
rejects the registration attempt of the mobile device.
[0007] In view of the above, there is a need in the art for a method and
apparatus for
efficiently selecting and acquiring a wireless communications system.
SUMMARY OF THE INVENTION
[0008] The present invention is a method and apparatus for efficiently
selecting and
acquiring a wireless communications system. In a preferred embodiment, a
mobile
station selects a group of wireless communications systems in accordance with
a
predetermined system acquisition procedure. The selected group of systems has
an
order of priority, such as a preference order determined by a wireless
services provider,
that may be used by the mobile station during system acquisition and
registration
attempts. Next, received signals corresponding to each of the selected systems
are
analyzed to determine the likelihood that each of the corresponding systems
would be
acquired by the mobile station. The group of wireless communications systems
is then
reprioritized based on the results of the analysis to produce a more efficient
system
acquisition order. The mobile station attempts to acquire and register with
one of the
systems in the reprioritized group of wireless communications systems in
accordance
with the acquisition order specified by the group.
[0009] The mobile station preferably includes processing circuitry, a memory,
a
communications transceiver and an antenna. The processing circuitry includes a
control
processor for controlling the operation of the mobile station, a signal
processor, a
searcher and a system determination unit. In a preferred embodiment, the
mobile station
is a mufti-mode device and the processing circuitry is adapted to operate in
either
CDMA or AMPS mode. The memory preferably includes both volatile and
nonvolatile
CA 02474506 2004-07-23
WO 03/067918 PCT/US03/03625
4
random access memories that store a preferred roaming list, including a
systems table
and an acquisition table, and one or more lookup tables such as a candidates
list. The
system determination unit is adapted to select one or more wireless
communications
systems from the systems table in accordance with a system acquisition
procedure. In a
preferred embodiment, the system determination unit stores the selected
systems in the
candidates list and instructs the searcher to analyze a received signal
corresponding to
each of the systems in the candidates list. For each listed system, the
searcher instructs
the transceiver to switch to the system's corresponding channel and a received
signal is
analyzed. The analysis of the received signals may include measuring the
received
signal strength (Rx) of each system, measuring the signal to noise ratio
E~/Io, or other
tests that assist in determining whether the candidate system is likely to be
acquired,
provided that the test requires less than time than a complete system
acquisition and
registration attempt.
[0010] After each system is analyzed, the group of selected systems is
reprioritized
based on the results of the analysis. In a preferred embodiment, all of the
systems are
orted such that those systems having the highest likelihood of being acquired
are
selected first. In a first alternative embodiment, the order of desirability
is maintained
and, at each level of desirability, the selected systems are sorted using the
analysis
results. In a second alternative embodiment, the desirability information for
each
selected system is adjusted based on the analysis results and the group of
selected
systems is then sorted using the adjusted desirability information. In a third
alternative
embodiment, each system having a corresponding analysis result that is lower
than a
threshold value is removed from the group of selected systems.
[0011] The mobile station next attempts to acquire and register with a
wireless
communications system. The system having highest level of priority is selected
first
from the reprioritized candidates list and an attempt is made to acquire and
register with
the selected system. Any system acquisition method may be used including
conventional system acquisition methods that are well-known in the art. If the
acquisition/registration attempt is not successful, then the wireless
communications
system having the next highest priority is selected from the candidate's list
and another
acquisition/registration is attempted. This process continues until a system
acquisition/registration attempt is successful, or until there are no
additional candidate
systems. In a preferred embodiment, if the acquisition/registration attempt is
successful
the wireless communications system is used for future wireless communications
CA 02474506 2004-07-23
WO 03/067918 PCT/US03/03625
services. In an alternative embodiment, the acquired wireless communications
system
has a known geographic region arid an attempt is made to acquire and register
with a
more preferred wireless communications system in the geographic region.
[0012] In a first alternative system acquisition sequence, a first system is
selected in
accordance with a system acquisition procedure. Any system acquisition
procedure
may be used, including selecting the system that was the most recently used by
the
mobile station. The signal quality of the selected system is measured and if
the system
is not likely to be acquired, then the next system is selected in accordance
with the
system acquisition procedure. If a selected system is likely to be acquired
then an
attempt is made to acquire and register with the selected system. If the
acquisition/registration attempt is successful then the wireless
communications system
is used for future wireless communications services. Otherwise, the next
system is
selected in accordance with the system acquisition procedure.
[0013] A more complete understanding of the Method and Apparatus for Efficient
Selection and Acquisition of a Wireless Communications Systems will be
afforded to
those skilled in the art, as well as a realization of additional advantages
and objects
thereof, by a consideration of the following detailed description of preferred
embodiments. Reference will be made to the appended sheets of drawings, which
will
first be described briefly.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The features, objects, and advantages of the present invention will
become more
apparent from the detailed description set forth below when taken in
conjunction with
the drawings in which like reference characters identify correspondingly
throughout and
wherein:
[0015] Fig. l illustrates a preferred embodiment of the present invention;
[0016] Fig. 2 is a mobile station in accordance with a preferred embodiment of
the
present invention;
[0017] Fig. 3a is a systems table in accordance with a preferred embodiment of
the
presentinvention;
[0018] Fig. 3b is an acquisition table in accordance with a preferred
embodiment of the
presentinvention;
[0019] Fig. 4 illustrates preferred lookup tables used by the mobile station
in
accordance with a preferred embodiment of the present invention;
CA 02474506 2004-07-23
WO 03/067918 PCT/US03/03625
6
[0020] Fig. 5 is a flow diagram illustrating a preferred system selection and
acquisition
procedure; and
[0021] Fig. 6 is a flow diagram illustrating an alternative system selection
and
acquisition procedure.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
[0022] A preferred embodiment of the present invention will now be described
with
reference to Fig. 1. A mobile station 2 operates in a geographic region 4 that
is serviced
by at least one base station 6. Each base station 6 is connected to a network
8, which is
part of a larger wireless communications system that supports at least one
multiple-
access wireless communications protocol, such as code . division multiple
access
(CDMA), wideband CDMA (WCDMA), Advanced Mobile Phone Service (AMPS),
Global System for Mobile communications (GSM), General Packet Radio Services
(GPRS) or High Data Rate (HDR) technology (e.g., lxEV technology). The mobile
station 2 may be any wireless device, whether stationary or mobile, that is
adapted for
wireless communications with at least one base station 6, such as a cellular
telephone,
pager, personal digital assistant (PDA), vehicle navigation system or portable
computer.
In a preferred embodiment, the mobile station is a multi-mode device that is
adapted to
operate in both CDMA and AMPS modes.
[0023] The mobile station 2 includes a list of known wireless communications
systems,
such as preferred roaming list (PRL) 10. The PRL 10 is stored in a nonvolatile
memory
of the mobile station 2 and includes a list of wireless communications systems
and
corresponding acquisition parameters that are used by the mobile station 2
during
attempts to acquire and register with a wireless communications system. In a
preferred
embodiment, the wireless communications systems listed in the PRL 10 are
grouped by
geographic region and sorted from the most desirable to the least desirable
system in
each region. As known in the art, the PRL 10 may be maintained by the mobile
station's wireless service provider and include a list of wireless
communications
systems that are available to the mobile station 2 through its wireless
service provider or
other wireless service providers that have agreed to provide roaming services
to the
mobile station 2.
[0024] In operation, the mobile station 2 attempts to acquire and register
with an
available wireless communications system that offers wireless services to the
mobile
station 2. First, a group of wireless communications systems is selected from
the PRL
CA 02474506 2004-07-23
WO 03/067918 PCT/US03/03625
7
in accordance with a predetermined system acquisition procedure. The group of
systems has an order of priority that may be used by the mobile station 2
during system
acquisition and registration attempts. For example, in a preferred embodiment
the
wireless communications systems in the mobile station's geographic region 4
are
selected and sorted from the most desirable to the least desirable system in
each region.
Next, received signals corresponding to each of the selected systems are
analyzed to
determine a relative likelihood that each of the corresponding systems would
be
acquired by the mobile station 2. The group of wireless communications systems
is
then reprioritized based on the results of the analysis to produce a more
efficient system
acquisition order. The mobile station 2 selects the system from the
reprioritized group
that has the highest relative priority and attempts to acquire and register
with the
selected system. If the acquisition/registration attempt is successful, the
selected system
is used by the mobile station 2 for wireless communications. Otherwise, an
attempt is
made to acquirelregister with the system from the group having the next
highest
priority.
[0025] Referring to Fig. 2, a preferred embodiment of the mobile station 2
will now be
described. The mobile station 2 includes processing circuitry 80, a memory 82,
a
communications transceiver 84 and an antenna 86. The processing circuitry 80
preferably includes a control processor 90 for controlling the operation of
the mobile
station 2, a signal processor 92, a searcher 94 and a system determination
unit 96. The
memory 82 preferably includes both volatile and nonvolatile random access
memories
that store a preferred roaming list, including a systems table 100 and an
acquisition table
102. The memory 82 may also store one or more lookup tables, such as a list of
the
most recently used systems 106, and program instructions for execution by the
processing circuitry 80.
[0026] The searcher 94 is adapted to identify valid signals, such as pilot
signals,
synchronization channels and paging channels received by the transceiver 84
through
the antenna 86. The design and implementation of searcher hardware for CDMA
acquisition is described in U.S. Patent No. 5,109,390, entitled "DIVERSITY
RECEIVER IN A CDMA CELLULAR TELEPHONE SYSTEM," assigned to the
assignee of the present invention, and is incorporated herein by reference.
The searcher
94 is further adapted to perform a preliminary acquisition analysis of one or
more
candidate communications systems.
CA 02474506 2004-07-23
WO 03/067918 PCT/US03/03625
8
[0027] The system determination unit 96 is adapted to select one or more
wireless
communications systems from the systems table 100 and retrieve corresponding
acquisition parameters from the acquisition table 102. The system
determination unit
96 is further adapted to forward the acquisition parameters to the searcher
94, which
attempts to acquire one the selected systems. In an alternative embodiment,
the system
determination unit 96 determines whether the current wireless communications
system
is the most desirable system in the mobile device's current geographic region
and, when
more desirable systems are available, initiates attempts by the mobile station
2 to
acquire a more desirable system. A method and apparatus for performing
preferred
system selection in a mobile station that is capable of operation in a
plurality of
geographic regions is disclosed in U.S. Patent No. 6,085,085, entitled "METHOD
AND
APPARATUS FOR PERFORMING PREFERRED SYSTEM SELECTION," assigned
to assignee, and is incorporated herein by reference.
[0028] It should be appreciated that the mobile station 2 illustrated in Fig.
2 is merely
illustrative and that alternative configurations and additional features are
contemplated
within the scope and spirit of the present invention. For example, the
components of the
mobile station 2 may be implemented in numerous hardware configurations using
conventional circuit elements such as one or more processors, memories and
application
specific integrated circuits (ASICs). The mobile station 2 may also be adapted
for voice
communications, high-speed data communications, video communications, Internet
applications such as email and World Wide Web access, position location (e.g.,
gpsOneTM developed by assignee), personal navigation, voice recognition,
integrated
removable storage devices and short-range wireless connectivity with local
peripherals
and devices. In a preferred embodiment, the processing circuitry 80 includes a
Mobile
Station Modem chipset, developed by assignee, which integrates digital and
analog
functions along with GPS-based position location.
[0029] Referring to Figs. 2 and 3a, a preferred embodiment of the systems
table 100
will now be described. The systems table 100 includes a list of wireless
communications systems that the mobile station 2 uses during attempts to
acquire and
register with a wireless communications system. As illustrated, each record in
the
systems table 100 preferably includes a system identifier (Sll~) 100a, a
network
identifier (NID) 100b, an indication of whether the system is preferred or
negative (P/N)
100c, an identifier of the geographic region (Region) 100d that is covered by
the
system, desirability information 100e and a pointer (AT Pointer) 100f to a
record in the
CA 02474506 2004-07-23
WO 03/067918 PCT/US03/03625
9
acquisition table 102. Each wireless communications system listed in the
systems table
100 is identified through a unique Sll~ 100a, NID 100b pair and is designated
as either a
preferred system that may be used by the mobile station 2 during roaming, or a
negative
system that should not be used by the mobile device 2 during roaming through
P/N
100c. In alternative embodiments, the wireless communications systems listed
in the
systems table 100 may be identified using other system identifiers, such as a
unique
band, mode and frequency, and Internet Protocol Version 6 (IPV6) address or a
Public
Land Mobile Network (PLMN) identifier. The wireless communications systems are
preferably grouped by geographic region 100d and stored in the systems table
100 in
sorted order from the most desirable system to the least desirable system in
each region
using thedesirability information 100e.
[0030] Referring to Fig. 3b, a preferred embodiment of the acquisition table
102 will
now be described. The acquisition table 102 includes a list of parameters that
are
necessary for the acquisition of the wireless communications systems listed in
the
systems table 100. As illustrated, each record in the acquisition table 102
preferably
includes a mode 102a, a band 102b and a frequency 102c. The systems table 100
and
the acquisition table 102 are preferably stored in a nonvolatile memory and
updated
periodically by an external source, such as the mobile station's wireless
service
provider, through downloads across a wireless connection or through another
data
transfer method. It will be appreciated that alternative configurations for
the PRL, the
systems table 100 and the acquisition table 102, and alternative
identification and
acquisition parameters may be used in accordance with the present invention.
[0031] As illustrated in Fig. 4, the memory also includes one or more lookup
tables 104.
In a preferred embodiment the lookup tables include a most recently used
(MRII)
systems table 104a that stores a list of the systems most recently used by the
mobile
station 2, a candidates list 104b that includes a list of systems that have
been selected as
candidates for acquisition, and a preferences table 104c that maintains local
preference
settings for the mobile station 2. Other information may also be stored in a
lookup table
including historical information that tracks the use of each system. The
lookup tables
are preferably stored in volatile portion of the memory 24, but in alternate
embodiments,
one or more of the lookup tables may be stored in a nonvolatile portion of the
memory
24.
[0032] A preferred system acquisition sequence for the mobile station 2 will
now be
described with reference to Fig. 2 and the flow diagram of Fig. 5. The system
CA 02474506 2004-07-23
WO 03/067918 PCT/US03/03625
acquisition sequence is preferably performed by the system determination unit
96. In
Step 200, a group of wireless communications systems is selected from a stored
list of
systems in accordance with a predetermined system acquisition procedure. In a
preferred embodiment, wireless communications systems in the mobile station's
geographic region 4 are selected from the system table 100, and the
corresponding
system identifiers are stored in the candidates list 104b in the memory 24. In
alternative
embodiments, the candidates list 104b may include other data such as
corresponding
acquisition parameters and desirability information for the selected systems.
The
candidates list 104b is preferably sorted in an initial order of priority
(e.g., from the
most desirable system to the least desirable system) as determined by the
predetermined
'system acquisition procedure. Although system selection using a PRL is
illustrated, it
will be appreciated that the other system acquisition procedures may be used
in
accordance with the preferred embodiment of the present invention. For
example, in
alternative embodiments the system acquisition procedure may include selecting
a
group of systems from the MRU 104a or other stored systems lists.
[0033] As known in the art, the system table 100 specifies a preferred system
acquisition order to be used by the mobile station 2 during system
acquisition/registration attempts. This system acquisition order, however, is
not always
the most efficient system selection order for acquiring and registering with a
wireless
communications system. The selection order specified by the system table 100
is
typically determined by the mobile station's wireless services provider based
on factors
that are unrelated to the likelihood that each of the listed systems will be
acquired by the
mobile station 2. For example, the desirability of each system may be
determined using
criteria such as the cost of using the system, the quality of the
communications service
offered by the system, protocol used by the system, support for unique
features and
whether the mobile station 2 is listed as a subscriber of the wireless
communications
system.
[0034] To improve the efficiency of the system acquisition/registration
process, the
mobile station 2 analyzes a received signal corresponding to each of the
systems in the
candidates list 104b (Step 202) and adjusts the system acquisition order based
on the
results of the analysis (Step 204). In a first preferred embodiment, the
analysis of the
received signals includes measuring the received signal strength (Rx) of each
system.
In operation, the searcher 94 steps through the systems identified in the
candidates list
104b stored in the memory 24. In an alternative embodiment, the candidates
list may be
CA 02474506 2004-07-23
WO 03/067918 PCT/US03/03625
11
transmitted to the searcher 94 from the system determination unit 96. For each
listed
system, the searcher 94 instructs the transceiver 84 to switch to the system's
corresponding channel. The received signal strength is then measured and
stored in the
candidates list 104b. If the received signal strength measurement is
relatively low, there
would be a low probability that the candidate system would be available for
acquisition.
If the received signal strength measurement is relatively high, there would be
a greater
probability that the candidate system could be acquired. It will be
appreciated that
signal strength measurements for a group of systems can typically be completed
in
significantly less time than an attempt to acquire and register with each
system in the
group. In alternate embodiments, other tests that assist in determining
whether the
candidate system is likely to be acquired may be performed on the received
signals.
[0035] In a first alternative embodiment, the analysis of the received signals
includes
determining whether the received signal is likely to be a CDMA signal. In this
embodiment, the system determination unit 96 instructs the searcher 94 to
measure the
signal to noise ratio E~Io, where E~ is the strength of the received signal
and Io is the
total thermal noise received on the channel. In a CDMA system, this
measurement
provides an indication of the portion of the received signal that is usable.
If the ratio
E~/Io is relatively large, then there is a high probability that the system
could be
acquired. The'ratio E~/Io provides a more reliable indication of whether the
signal is
likely to be acquired than the measured raw strength of the signal.
[0036] In a second alternative embodiment, the system determination unit 96
and
searcher 94 support multiple test modes and methods of acquisition, and may be
adapted
to use more than one type of analysis, alone or in combination. The test mode
may be
determined by user preference, configuration of the mobile station, current
operating
state of the mobile station or other criteria. The searcher 94 preferably
operates in
accordance with instructions received from the system determination unit 96
and the
system determination unit 96 is adapted to transmit a candidate systems test
instruction
and a system acquisition instruction. The candidate systems test instruction
includes
parameters to identify the candidate list, an identifier of the test to be
performed on each
candidate system and a minimum threshold value to be met by each system. The
searcher 94 executes the received instruction and returns the candidate
systems that
meet the testing requirements. In a preferred embodiment, the searcher 94
modifies the
candidates list stored in memory. The system determination unit 96 is further
adapted
a
CA 02474506 2004-07-23
WO 03/067918 PCT/US03/03625
12
to analyze the test results and transmit a system acquisition instruction to
the searcher
94, including parameters identifying the candidates lists.
[0037] In Step 204, the group of selected systems is reprioritized based on
the analysis
to produce a more efficient system acquisition order. In a preferred
embodiment, all of
the systems are sorted such that those systems having the highest likelihood
of being
acquired are selected first. In a first alternative embodiment, a plurality of
the selected
systems have the same level of desirability. At each level of desirability,
the selected
systems are sorted using measured signal strength, from the most likely system
to be
acquired to the least likely system to be acquired. In a second alternative
embodiment,
the desirability information for each selected system is adjusted based on the
test
measurement. For example, the relative desirability of systems having a signal
strength
measurement greater than a first threshold value may be adjusted upward, while
the
relative desirability of systems having a signal strength lower than a second
threshold
value may be adjusted downward. The group of selected systems is then sorted
using
the adjusted desirability information. In a third alternative embodiment,
systems having
a tested signal quality that is lower than a threshold value are removed from
the group
of selected systems. For example, candidate systems that have a corresponding
measured signal strength lower than -90db may be eliminated from the
candidates list.
Other criteria may also be used to eliminate and sort candidate systems. For
example, a
weighting factor may be used that takes into account the measured signal
strength,
whether the system was recently used, the desirability rating and other
information.
[003] After the group of selected systems is reprioritized, the mobile station
2 attempts
to acquire and register with one of the wireless communications systems in the
group.
In Step 206, the system having highest level of priority is selected from the
candidates
list 104b. In a preferred embodiment, this system has a relatively high
desirability level
and a high likelihood that the acquisitionlregistration attempt will be
successful based
on a measured signal quality such as a signal strength measurement. An attempt
is
made to acquire and register with the selected system in Step 208. Any system
acquisition method may be used including conventional system acquisition
methods that
are well-known in the art. In a preferred embodiment, the mobile station 2 is
adapted to
acquire a CDMA system. To acquire a CDMA system, the searcher 94 instructs the
transceiver 84 to switch to the communications channel of the selected CDMA
system
and listens for a pilot signal. The searcher 94 attempts to verify the
received pilot signal
by testing various pseudorandom noise (PN) offsets in the received signal
until a match
CA 02474506 2004-07-23
WO 03/067918 PCT/US03/03625
13
is found. When the pilot signal is acquired, the processing circuitry 80
receives
information for the forward CDMA channel and a phase reference for signal
demodulation. Next, the processing circuitry 80 attempts to acquire the
synchronization
channel associated with the identified pilot channel. The synchronization
channel
transmits basic system information such as the unique SID/NID of the
transmitting
wireless communications system and network, and synchronization information.
The
processing circuitry 80 adjusts its timing in accordance with the received
information
and then switches to the base station's paging channel. The paging channel is
used by a
local base station of the current communications system to communicate with
the
mobile station 2 when the mobile station 2 is not assigned to a traffic
channel. Through
the paging channel, the base station notifies the mobile station 2 of incoming
messages,
such as an incoming telephone call or a notification of a received voicemail
message.
[0039] If the acquisition/registration attempt is successful (Step 210) then
the selected
system is used by the mobile station 2 for wireless communications. If the
acquisition/registration attempt is not successful, the wireless
communications system
having the next highest priority is selected from the candidate's list in Step
212 and
control returns to Step 208 for the next acquisition/registration attempt. If
the searcher
94 is unable to acquire the selected system (Step 210) the searcher 94 will
attempt to
acquire each of the remaining systems according to the selection order until a
wireless
communications system is acquired or the candidate systems are exhausted. In
an
alternative embodiment, if the acquisition/registration attempt is successful
in Step 210,
then the process returns to Step 200 for the selection of a group of systems
in the current
geographic region that are more desirable than the selected system.
[0040] An alternative system acquisition sequence is illustrated in the flow
diagram of
Fig. 6. In Step 250, a first system is selected in accordance with a system
acquisition
procedure. Any system acquisition procedure may be used, including selecting
the
system that was the most recently used by the mobile station 2. The signal
quality of
the selected system is measured in Step 252. If the system is likely to be
acquired (Step
254) then an attempt is made to acquire and register with the selected system
in Step
256. In a preferred embodiment, the system is likely to be acquired if the
measured
signal quality exceeds a predetermined threshold value. If the system is not
likely to be
acquired, then the next system is selected in accordance with the system
acquisition
procedure in Step 260. If the acquisition/registration attempt is successful
(Step 258)
then the mobile station 2 uses the selected system for future wireless
communications
CA 02474506 2004-07-23
WO 03/067918 PCT/US03/03625
14
services. If the acquisition/registration attempt is not successful then the
next wireless
communications system is selected in Step 260 and control returns to Step 252.
[0041] Having thus described a preferred embodiment of the Method and
Apparatus for
Efficient Selection and Acquisition of a Wireless Communications System, it
should be
apparent to those skilled in the art that certain advantages of the within
described system
have been achieved. It should also be appreciated that various modifications,
adaptations, and alternative embodiments thereof may be made within the scope
and
spirit of the present invention.
[0042] The scope of the present invention is defined by the following claims.
