Note: Descriptions are shown in the official language in which they were submitted.
CA 02287243 1999-10-13
WO 98/47238 PCT/US98/07433
Croas-Reference To Related Patent Applications
The present invention is related to the subject
matter of the provisional United States Patent
Application entitled ~~Selection of Alternate Frequency in
CDMA System for Multiple Frequencies in One Cell,~~ filed
14 April 1997, Serial No. 60/043,546 (Northern Telecom
Incorporated Docket No. RR-2163P), assigned to the
assignee herein named. Applicants hereby claim the
benefit under 35 U.S.C.~~ 119(e) of this foregoing
related provisional application. The contents of the
above-mentioned provisional patent application is
incorporated by reference herein.
Background of the Invention
The present invention relates, in general, to a
method and system to be utilized with wireless
communications systems having cellular architectures. In
particular, the present invention relates to a method and
system, to be utilized with wireless communications
systems having cellular architectures which utilize Code
Division Multiple Access (CDMA). Yet still more
particularly, the present invention relates to a method
' and system, to be utilized with wireless communications
systems having cellular architectures which utilize CDMA,
and which increase the reliability of such wireless
communications systems by avoiding communication failure.
CA 02287243 1999-10-13
WO 98/47238 PCT/US98/07433
2
The present invention is related to wireless
communication systems, and, in particular, to wireless
communications systems which have both a cellular
architecture ie.g., cellular telephony, personal
communications systems) and which utilize CDMA (or
similar technologies). Wireless communication refers to
the fact that transmission between sending and receiving
stations occurs via electromagnetic radiation not guided
by any hard physical path (e. g. by microwave link).
Cellular architecture refers to the fact that the
wireless system effects service over an area by utilizing
a system that can be (ideally) be pictographically
represented as a cellular grid. CDMA stands for Code
Division Multiple Access, which is a type of spread
spectrum technology, originally developed for military
application and thereafter adapted for civilian use.
Wireless cellular communication utilizing CDMA is
the latest incarnation of a technology that was
originally known as mobile telephone systems. Early
mobile telephone system architecture was structured
similar to television broadcasting. That is, one very
powerful transmitter located at the highest spot in an
area would broadcast in a very large radius. If a user
were in the usable radius, then that user could broadcast
to the base station and communicate by radio telephone to
the base station. However, such systems proved to be _
very expensive for the users and not very profitable to
the communication companies supplying such services. The
primary limiting factor of the original mobile telephone
systems was that the number of channels available for use
was limited due to severe channel-to-channel interference
within the area served by the powerful transmitter.
CA 02287243 1999-10-13
WO 98147238
3
PCTNS98/07433
Counter-intuitively, engineers discovered that
channel-to-channel interference effects within the
service area were not related solely to the distance
between stations communicating with a base station
' transmitter (which intuitively would seem to give rise to
the interference), but were also related inversely to the
usable radius of the roughly circular area being served
by a base station transmitter. Engineers found that by
reducing the radius of an area being served by a base
station transmitter by a significant percentage, channel-
to-channel interference effects were reduced such that a
significant increase in the number of additional usable
channels could be provided. For example, it was found
that a system based on an area being served by a base
station transmitter with a one-kilometer useable radius
would have 100 times more usable channels than a system
based on an area being served by a base station
transmitter with a 10-kilometer useable radius.
Reducing the power of the central transmitter
allowed a significant increase in the number of available
channels by reducing channel-to-channel interference
within an area. However, as the power of the central
transmitter was reduced, the serviceable area was also
reduced. Consequently, although reducing transmission
power increased the number of available channels, the
small service area provided by such reduced power did not
make such radio telephone systems attractive
communication options for many users. Thus, a problem
arose relating to how to utilize the discovery that
smaller area size (or, equivalently, reduced transmitter
power) increased the available channels such that radio
telephone systems based on such smaller areas would be
commercially viable.
I 1
CA 02287243 1999-10-13
WO 98/47238 PCTlUS98/07433
4
This problem was solved by the invention of the
wireless cellular architecture concept. The wireless
cellular architecture concept utilizes geographical
subunits called "cells" and encompasses what are known as
the "frequency reuse" and "handoff" concepts. A cell is
the basic geographic unit of a cellular system. Cells
are defined by base stations (a base station consists of.
hardware located at the defining location of a cell and
includes power sources, interface equipment, radio
frequency transmitters and receivers, and antenna
systems) transmitting over small geographic areas that
are represented (ideally) as hexagons. The term
"cellular" comes from the honeycomb shape of the areas
into which a coverage region, served via two or more base
stations, is divided when the mathematically ideal
hexagonal shape used to represent the usable geographic
area of each of the two or more base stations. It is to
be understood that, although the mathematically ideal
shape of the cell is a hexagon, in practicality each cell
size varies dependent upon the landscape (e. g., a base
station transmitting on a flat plane will closely
approximate the ideal hexagon, whereas a base station
transmitting in a valley surrounded by.hills will not
closely approximate a hexagon due to the interference
from the surrounding hills).
Within each cell a base station controller talks to
many mobile subscriber units at once, utilizing one
defined transmit/receive communications channel for each
mobile subscriber unit with which communication is taking
place. Each mobile subscriber unit (a control unit and a
transceiver that transmits and receives wireless
transmissions to and from a cell site) uses a separate,
temporarily assigned transmit/receive wireless channel to
talk to a cell site. Each wireless transmit/receive
CA 02287243 1999-10-13
PCTNS98/07433
WO 98147238
communications channel consists of a pair of frequencies
for communication -- one frequency for transmitting from
the cell site base station controller to the mobile
subscriber unit, named the forward link, and one
frequency for transmitting from the mobile subscriber
unit to the cell site base station controller, named the
reverse link.
Wireless communication is regulated by government
bodies (e.g., the Federal Communications Commission in
the United States). Government bodies dictate what
frequencies in the wireless spectrum can be used for
particular applications. Consequently, there is a finite
set of frequencies available for use with cellular
communications. The frequency reuse concept is based on
the assigning to each cell a group of radio channels to
be used within the small geographic area (cell).
Adjacent cells are assigned groups of channels that are
completely different from the groups of channels assigned
to neighboring cells. Thus, in the frequency reuse
concept there is always a buffer cell between two cells
utilizing the same set of frequencies. The cells are
sized such that it is not likely that two cells utilizing
the same set of frequencies will interfere with each
other. Thus, such a scheme allows "frequency reuse" by
non-adjacent cells. As mobile subscriber units transit
adjacent cells, the mobile subscriber unit is "handed"
from a cell it is leaving into a cell it is entering by
directing the mobile subscriber unit to stop using
' frequencies appropriate to the cell it is leaving and to
begin using frequencies appropriate to the cell it is
' entering. Thus, the cellular architecture concept, in
conjunction with the frequency reuse concept, augmented
by the operation of "hand-off" gave rise to the ability
CA 02287243 1999-10-13
WO 98147238 PCTIUS98/07433
6
to utilize small cells to provide communications service
over a large geographic area.
The first large-scale wireless communications system
utilizing cellular architecture in North America was the
Advanced Mobile Phone Service (AMPS) which was released
in 1983. With the introduction of AMPS, user demand for
bandwidth was initially iow until users became acquainted
with the power of the system. However, once users became
acquainted with the power of cellular, the demand for the
service increased. Very quickly, even the extended
number of channels available utilizing the cellular
concepts of reduced power output and frequency reuse were
quickly consumed by user demand in certain geographic
areas, and a problem arose with respect to capacity.
Engineers responded to the problem by devising the
Narrowband Analog Mobile Phone Service (NAMPS). NAMPS
utilizes frequency division multiplexing to transmit
three transmit/receive channels in the same bandwidth
wherein AMPS had previously only transmitted one
transmit/receive channel. Thus, NAMPS essentially
tripled the capacity of AMPS. However, even though NAMPS
essentially tripled the capacity of AMPS, the extended
number of channels available with NAMPS were quickly
consumed by user demand in certain geographic areas, and
a problem again arose with respect to capacity.
Engineers responded to this new problem by devising
Digital AMPS (or DAMPS, also known as TDMA). In
DAMPS/TDMA time division multiple access techniques are
utilized to multiplex user data together. Furthermore,
digital data compression techniques are utilized at both
the transmission and reception ends. These techniques
give rise to increased capacity, and clarity, even
CA 02287243 1999-10-13
WO 98/47238 PCT/US98/07433
7
exceeding that of NAMPS. However, as was the case with
both AMPS and NAMPS, the increased bandwidth capacity of
DAMPS/TDMA has been quickly consumed by user demand in
certain geographic areas.
Subsequent attempts to increase cellular telephony
bandwidth capacity tended to be variations on the
foregoing described themes. However, it became apparent
that some new communications technology would be
necessary to give rise to any significant increase in
bandwidth beyond that available with the foregoing
described technologies. It was decided within the
industry that such new technology would be standard CDMA,
which stands for Code Division Multiple Access.
Notice that in all the foregoing described
technologies, the method of using multiple
transmit/receive channels with each such transmit/receive
channel utilizing a different pair of frequencies was
maintained throughout. Standard CDMA breaks completely
with this method of communication.
Standard CDMA utilizes cellular architecture and a
type of hand-off. However, in standard CDMA,
transmission and reception is done by ali users on the
same frequency. Standard CDMA is able to achieve this
feat by insuring that the signals from different users
are adjusted such that the signals do not interfere with
each other to the point of being unable to understand the
' messages from the different users.
The way in which standard CDMA works is somewhat
analogous to a situation in which two English speaking
persons are communicating in a room wherein many other
non-English speakers are also communicating in a language
CA 02287243 1999-10-13
WO 98/47238 PCT/US98/07433
8
which the two English speakers do not understand. Since
the two English speakers do not understand the language
spoken by the non-English speakers in the room, the
conversations of their non-English-speaking counterparts
will be interpreted by the two English speakers as
meaningless "noise." Consequently, since the English
speakers will attach no meaning to the "noise," the
English speakers will be able to disregard the "noise"
and continue to engage in their conversation provided
that they both speak loudly enough so that each can be
understood by the other despite the "noise" generated by
their non-English-speaking counterparts. This is true
even though all persons in the room are talking, or
communicating, in the same band of sound frequencies
which the human ear can hear.
Standard CDMA is able to achieve the same affect by
modulating the signal of each user within a particular
cell with a "pseudo-noise" code which, in effect, will
make each user in the cell appear as if each user were,
in effect, "speaking a different language," thereby
insuring that the meaning of a signal generated by one
user within the cell will not be drowned out by the
meaning contained within the signal generated by one or
more other users in the cell. Provided, of course, that
each user speaks "loudly" enough (or transmits enough
power) to be understood over the "noise" generated by the
other users in the CDMA cell.
Standard CDMA utilizes digital data technology to
achieve the foregoing. Standard CDMA utilizes complex
digital codes to modulate user data prior to transmission
within a cell. The standard CDMA pseudo-noise codes are
chosen such that a modulated signal, when transmitted
upon a carrier frequency within the cell, approximates
CA 02287243 1999-10-13
WO 98/47238 PCT/US98/07433
9
white (or Gaussian) noise, and does nvt greatly interfere
with any other signal transmitted upon the same carrier
frequency within the cell. Upon reception,.a similar
pseudo-noise code is used to demodulate the signal and
recover the data that was transmitted.
When digital data technology is utilized with the
standard CDMA pseudo-noise codes, it is necessary for all
transmitters and receivers within a cell to be
synchronized to the same digital clock. This
synchronization is provided by use of a "pilot" signal
which is transmitted by the base station. Each mobile
subscriber unit within a cell "locks" to this pilot
signal and thereafter utilizes it as the clock signal for
digital data-processing.
Tn standard CDMA, each base station transmits and
receives on the'same carrier frequency. Furthermore, in
standard CDMA, each base station transmits the same
period digital code which is utilized as the pilot signal
within each cell. Ordinarily, such a situation would
give rise to severe interference between cells. Standard
CDMA avoids this problem by phase-shifting (or time-
staggering) the pilot signal, or digital code,
transmitted within adjacent cells. Within standard CDMA,
the carrier signal, pilot code, pseudo-noise codes, and
phase-shifting (or time-staggering) of the pilot codes
utilized in adjacent cells have all been chosen to work
together such that inter-cell interference is minimized.
Thus, not only does standard CDMA ensure that users in
each cell appear to each other as if they are "speaking
different languages," but standard CDMA ensures that
adjacent cells appear to each other "as if" each cell was
in fact "speaking a different language."
CA 02287243 1999-10-13
WO 98/47238 PCT/US98/07433
Although at first examination, it appears that
standard CDMA can provide virtually unlimited bandwidth,
in actuality standard CDMA has provided an increase in
capacity of only roughly I3 times that of AMPS. The
primary reason for this is known in the art as "the near-
far" problem. Returning to our analogy of two English
speakers communicating in a room full of other non-
English speakers, it is apparent that there is a
practical limit with respect to how far apart the English
speakers can be and still communicate. That is, due to
the "noise" produced by the non-English-speaking persons
in the room, there is a practical limit on how far apart
the English speakers can be and still be understood by
each other. This practical limit is dependent upon both
the "noise" in the room and the "volume" which can be
generated by each English speaker. That is, when the
English speakers are "near" each other, they can
communicate with relatively low "volume" (or "power"
output), but when they are "far" from each other they can
only communicate with relatively high "volume" (or
"power" output).
A similar "near-far" problem exists in standard CDMA
for roughly the same reasons. That is, the "noise" of
the other users in a cell gives rise to a requirement
that the mobile subscriber units in the cell increase
their power outputs dependent upon both noise in the cell
and the distance from the base station transceiver. This
"near-far" problem thus puts a practical limit on the
bandwidth available in standard CDMA, which has been
found empirically to have a practical upper limit of 13
times AMPS.
As was the case for original cellular, AMPS, and
DAMPS/TDMA, the additional bandwidth provided by standard
CA 02287243 1999-10-13
WO 98/47238 PCTIUS98/07433
I1
CDMA is being quickly consumed by users. Consequently,
newer CDMA systems are being developed to provide users
-with additional bandwidth. However, as will be shown in
the detailed description, such newer systems, in certain
instances, tend toward communication failure. It is
therefore apparent that a need exists for a method and
system which increase the reliability of such wireless
communications systems by avoiding communication failure
in the instances identified.
CA 02287243 1999-10-13
WO 98/47238 PCT/US98107433
12
Su~ana.ry of the Invention
It is therefore one object of the present invention
to provide a method and system to be utilized with
wireless communications systems having cellular
architectures.
It is therefore another object of the present
invention to provide a method and system, to be utilized
with wireless communications systems having cellular
architectures and which utilize CDMA.
It is yet another object of the present invention to
provide a method and system, to be utilized with wireless
communications systems having cellular architectures and
which utilize CDMA, and which increase the reliability of
such wireless communications systems by avoiding
communication failure.
The method and system achieve their objects as
follows. At least one CDMA carrier acquisition failure is
detected. Channel acquisition procedures are adjusted
such that the at least one CDMA carrier for which
acquisition failed is no longer considered a viable
channel. Channel acquisition failure detection can
include storing the identity of the at least one CDMA
carrier for which acquisition failed. Adjustment of
channel acquisition procedures can include removing the
at least one CDMA carrier for which acquisition failed -
from the list of carriers considered active. Adjustment
of channel acquisition procedures can also include
allowing CDMA carrier selection as if the detection of at
least one CDMA carrier acquisition failure had not
occurred, and, if the CDMA carrier selected is the at
CA 02287243 1999-10-13
WO 98/47238
13
PCTIUS98107433
least one CDMA carrier for which acquisition failed,
substituting another CDMA carrier in place of the CDMA
carrier selected. Furthermore, adjustment of channel
acquisition procedures can also include substituting a
new seed into the pseudo-random number generator
ordinarily utilized to select the CDMA carrier, and
thereafter utilizing the new seed with the pseudo-random
number generator ordinarily utilized to select the CDMA
carrier.
The above, as well as additional objects, features,
and advantages of the present invention will become
apparent in the following detailed written description.
CA 02287243 1999-10-13
WO 98147238 PCT/US98/07433
14
Brief Description of the Drawings
The novel. features believed characteristic of the
invention are set forth in the appended claims. The
invention itself, however, as well as a preferred mode of
use, further objects, and advantages thereof, will best
be understood by reference to the following detailed
description of an illustrative embodiment when read in
conjunction with the accompanying drawings, wherein:
Figure 1 depicts a mufti-carrier CDMA environment
wherein one embodiment of the present invention can be
practiced;
Figure 2 illustrates as closely as is practicable
the way in which an independent CDMA system, from a
mufti-carrier CDMA environment, is selected and also
illustrates a defect in the selection standards which
will cause a system failure;
Figure 3 is a high-level logic flow chart which
depicts a method by which an embodiment of the present
invention is able to alleviate system failure in an ANSI
J-STD-008 standard system; and
Figure 4 is a high-level logic flow chart which
depicts a method by which another embodiment of the
present invention is able to alleviate system failure in
an IS-95-A+TSB74 standard system.
CA 02287243 1999-10-13
WO 98/47238 PCT/US98I07433
Detailed Description of the Invention
As was noted in the background section, the
additional bandwidth provided by standard CDMA is
currently being consumed by users. Consequently, a
desire has arisen. to provide additional bandwidth above
and beyond that available with standard CDMA.
One attempt at providing such additional bandwidth
has focused on providing additional carriers within each
cell above and beyond that normally provided by standard
CDMA. That is, as was explained in the background, while
standard CDMA utilizes only one carrier within each cell,
newer experimental systems are being tried which attempt
to increase the bandwidth available in each cell by
providing, in effect, multiple independent CDMA systems
within each individual cell. For ease in
differentiation, the newer systems will be referred tv
herein as "multi-carrier CDMA" to distinguish them from
"standard" (one carrier) CDMA.
Such experimental systems are quite complex, in that
they attempt to coordinate users across the multiple
independent CDMA systems which are required to implement
mufti-carrier CDMA within an within an individual cell,
as well as coordinate user handoff between such multiple
independent CDMA systems within adjacent cells. One
facet of the way which this is achieved is by having the
mobile subscriber units determine, via communication with
base station controllers, the carrier frequencies
available within a cell and then making the individual
mobile subscriber units responsible far selecting one of
the available carrier frequencies for use. Figure 1
shows this operation pictographically.
CA 02287243 1999-10-13
WO 98/47238 PCT/US98/07433
16
Figure 1 depicts a multi-carrier CDMA environment
wherein one embodiment of the present invention can be
practiced. A "cell" is the basic geographic unit of a
cellular system generated by a base station transmitting
within a geographic area. The term "cellular" comes from
the honeycomb shape of the areas into which a coverage
region is divided. Illustrated in Figure 1 is CDMA cell
101 which is depicted as a honeycomb shape within which
base station 111 is shown. Cells are pictographic
representations of the effective geographic area of base
station (a base station includes but is not limited to
transmitters and receivers sufficient to service existing
cell channels within a particular cell) transmitters that
are for convenience represent as hexagons. Each cell
size varies dependent upon the landscape. Because of
constraints imposed by natural terrain and man-made
structures, the true shape of cells is not a perfect
hexagon.
Base station 111 is shown as having a multi-carrier
CDMA scheme supporting three separate, and independent,
CDMA systems: CDMA I system 121 transmitting on carrier
frequency F 1~ CDMA 2 system 131 transmitting on carrier
frequency F 2: and CDMA 3 system 141 transmitting on r
carrier frequency F 3. Also depicted is mobile subscriber
unit 151.
Forsake of illustration, it is to be assumed that
mobile subscriber unit 151 is being powered-up (i.e., is
being turned on) in CDMA cell 101. Upon power-up (i.e.,
being turned on) it is necessary for mobile subscriber
unit 151 to determine which of the three independent CDMA
systems it will utilize while it is in CDMA cell 101
CA 02287243 1999-10-13
WO 98/47238 PCT/US98/07433
17
that. This is illustrated in a general sense by method
flow steps '160-I70.
Method step 160 depicts the start of the process.
Method step 162 illustrates the event of power-up or any
other state where determination of which independent CDMA
system will be utilized is necessary (e. g., entering cell
I01 upon handoff, or re-acquiring a carrier when one
carrier has been lost). Method step 164 shows that
mobile subscriber unit 151 tunes to its primary channel
(a pre-assigned channel native to mobile subscriber unit
151 ) .
Method step 166 depicts that upon acquisition of the
primary channel, mobile subscriber unit 151 listens to
what is known as the "paging channel," upon which are
carried what are known as overhead messages, and
determines how many independent CDMA systems are
available in cell 101 and the carrier frequencies upon
which such independent CDMA systems are operating.
,Method step 168 illustrates that upon determination
of the number of independent CDMA systems, and the
carrier frequencies upon which the independent CDMA
systems are operating, in cell 10I, mobile subscriber
unit I51 selects one of the carrier frequencies upon
which one of the independent CDMA systems is operating.
Thereafter, method step 170 shows that mobile subscriber
unit 151 tunes to the selected carrier frequency and
begins interacting with the independent CDMA system
operating on that tuned-to carrier frequency.
Method steps 160-170 have illustrated generally how
the independent CDMA system is selected in a multi-
CA 02287243 1999-10-13
WO 98147238 PCT/US98/07433
18
carrier (as opposed to standard) CDMA system. However,
those skilled in the art will recognize that while the
operation is generally as depicted as shown in method
steps 160-170, the specific way in which such is done is
more complicated.
Refer now to Figure 2. Figure 2 illustrates as
closely as is practicable the way in which an actual
independent CDMA system, from a multi-carrier CDMA
environment, is selected as dictated by pages 6-97
through 6-123 of the Mobile Station-Base S a ion
r -M Wi n
+ n
l~ul~et~w SuRport far 14 4 kbps Data Rate and PCS
Interaction for Widebar~d Spread Sgp~trmm ypti">>r
Systems, TIS/EIA/IS-95-A+TS874 standard (27 February
1996) (hereinafter referred to as the "IS-95-A+TSB74
standard"): the IS-95-A+TSB74 standard is well-known to
those within the art. Figure 2 will also be used to
illustrate a defect in the ~S-95-A+TSB74 standard which
will cause a system failure.
Method step 200 shows the start of the process.
Method step 202 depicts power-up or entry into any other
state requiring CDMA channel (or CDMA independent system)
acquisition. .See IS-95-A+TSB74 page 6-97 for details.
Method step 204 illustrates the selection of a CDMA
system in accordance with the custom selection process.
See IS-95-A+TSB74 page 6-97 for details. Method step 206
shows the selection of either the primary or secondary
CDMA channel over which the mobile subscriber unit will
receive the "paging channel" (those skilled in the art
will recognize that the foregoing is a portion of the
Custom System Selection Process, which has many more
CA 02287243 1999-10-13
WO 98/47238 PCT/US98/07433
19
steps in addition to the foregoing described step;
however, for purposes of the present invention selection
of the primary or secondary CDMA channel is most
- relevant). See Is-95-A+TSB74 page 6-101 for details.
Method step 208 depicts the event of a mobile
subscriber unit listening to a "paging channel"
subsequent to tuning to either the primary or secondary
CDMA channel and receiving "overhead messages," one of
which is/contains a "CDMA Channel List Message." See IS-
95-A+TSB74 pages 6-116 to 6-lI7 for details. Method step
2I0 illustrates the extraction and saving of the number
(an integer) of and carrier frequencies of the
independent CDMA systems/channels available within a
cell; those skilled in the art will recognize that each
channel will be known by a non-negative integer number,
which the mobile subscriber unit will associate
internally with a channel operating at a given carrier
frequency. See IS-95-A+TSB74 page 6-123 for details.
Method step 212 illustrates the selection of a CDMA
system/channel which will be utilized by a mobile
subscriber unit. ~S-95-A+TSR74 page 6-123; 6-230 to 6-231
for details. Method step 214 shows that subsequent to
the selection of a CDMA system/channel (or carrier
frequency) a mobile subscriber unit makes an attempt to
tune in to the CDMA system/channel (or carrier frequency)
selected. IS-95-A+TSB74.
In the event that the mobile subscriber unit is able
to tune in to the CDMA system/channel (or carrier
frequency) selected, the process proceeds to method step
216 and stops.
CA 02287243 1999-10-13
WO 98/47238 PCT/US98/07433
In the event that the mobile subscriber unit is
unable to tune in to the CDMA system/channel (or carrier
frequency) selected, the process returns to method step
200. Thereafter, the process proceeds through the flow
again. Notice that no provision is made in the method
shown to "remember" either the fact that channel
acquisition failed, or the designation of the channel
associated with that failed acquisition. See IS95-95-
A+TSB74 page 6-230 to 6-231 for details.
The fact that no provision is made in the method
shown to "remember" the fact that channel acquisition
failed gives rise to severe and significant errors under
the IS-95-A+TSB74 standard. This error arises because no
provision is made under the IS-95-A+TSB74 standard to
remember either the specific channel upon which
acquisition failed, and/or utilize the identity of the
channel that failed to ensure that an attempt is not made
to re-acquire the channel upon which acquisition failed.
While the foregoing example dealt with the IS-95-
A+TS874 standard, those skilled in the art will recognize
that there are analogous standards in which similar
problems occur. One such standard is the
Station-Base Station Conmatibilitv Rec,~irements for 1.8
to 2.0 Ghz Code Division Multiple Access (CDMA) Personal
Conununications Systems, ANSI J-STD-008 standard (Original
Version 24 March 1995: Corrected Version 29 August 1995)
(hereinafter the "ANSI J-STD-008 standard").
Accordingly, one embodiment, described in Figure 3 below,
of the present invention solves the above identified
problem under the ~,NSI J-STD-008 standard. A second
embodiment of the present invention, described in Figure
CA 02287243 1999-10-13
WO 98147238 PCTIU598/07433
21
4 below, insures that the foregoing identified error does
not occur under the IS-95-A+TSB74 standard.-
Refer now to Figure 3. Figure 3 is a high-level
logic flow chart which depicts a method by which an
embodiment of the present invention is able to alleviate
the foregoing described problem. The high-level logic
flow chart of Figure 3 can be referenced specifically to
the ANSI J-STD-008 standard via the BSI J-STD-008
standard section numbers depicted in Figure 3 (e. g.,
2.6.1.1, 2.6.2.2.4, 2.6.1.2, and 2.6.1.3). That is, the
high-level logic flow chart depicted in Figure 3 is
intended to be used within the context of ANSI J-STD-008
systems to alleviate the foregoing noted problems extant
within the standard itself.
Method step 300 illustrates the start of the
process. Method step 302 shows the event of "power up,"
such as the event of a mobile subscriber unit being
turned on. Method step 304 depicts the mobile subscriber
unit engaging in the ANSI J-STD-008 "custom selection"
process in order to find and tune to an available CDMA
primary or secondary channel in a fashion dictated by
.ANSI J-$TD008008 standard section 2.6.1.1, which is shown
as CDMACHS being set equal to "C," which represents the
mobile subscriber unit being tuned to either its primary
or secondary channel.
Method step 306 depicts the default initialization
of parameters to be utilized by the process to ensure
that any CDMA carrier frequency selected is in fact one
that is operational; that is, method step 306 depicts the
initialization of the variables CDMACHT~,,p (which is used
to hold the value of the primary or secondary channel,
CA 02287243 1999-10-13
WO 98147238 PCT/US98/07433
22
"C," for reasons explained below) and CDMACHS to default
channel "C" (which was introduced in method.step 304),
and CDMACH-FAIL LIST to default value NULL (which merely
means that the list of failed CDMA carrier frequencies is
empty at initialization).
Method step 308 illustrates the receipt of a CDMA
carrier frequency (or "channel list") list message in a
fashion dictated by ANSI J-STD-008 standard section
2.6.2.2.4. Method step 310 shows that upon receipt of
the CDMA carrier frequency list a modified ANSI J-STD-008
hash algorithm is utilized to select a CDMA carrier
frequency; shown in method step 310 is that the selection
is done by selecting the CDMA carrier frequency from the
CDMA carrier frequencies indicated in the received CDMA
channel list message minus the CDMA carrier frequencies
(if any) contained within CDMACH_FAIL LIST (that is, the
list of failed CDMA carrier frequencies). Those skilled
in the art will recognize that there are numerous ways in
which the ANSI J-STD-008 hash algorithm can be modified
such that the foregoing is achieved, with such ways
including, but not limited to, (1) subtracting out the
failed CDMA carriers prior to initializing the ANSI J-
STD-008 hash algorithm; (2) allowing the ANSI J-STD-008
hash algorithm to operate "as if" the failed CDM'A carrier
frequencies had not been noted, and in the event that a
failed frequency (i.e., a channel contained within
CDMACH_FAIL LIST) is selected, then substituting for that
failed frequency an operative frequency (i.e., a carrier -
frequency which is within the received CDMA channel list,
but which is not contained within CDMACH FAIL LIST); or
(3) substituting a new seed, other than that associated
with any failed carrier frequencies contained within the
list of failed carrier frequencies CDMACH_FAIL LIST, into
the pseudo-random number generator ordinarily utilized
CA 02287243 1999-10-13
WO 98/47238 PCT/US98107433
23
under the ~1SI J-STD-008 standard to select a CDMA
carrier frequency.
Method step 312 depicts that subsequent to the
selection of a CDMA carrier frequency, an attempt is made
to first acquire the selected carrier frequency and then.
the "pilot" channel being broadcast within selected CDMA
frequency (if the selected carrier frequency has been
successfully acquired) in the fashion dictated by At'1-
STD-008 standard section 2.6.I. In the event that either
attempt is unsuccessful the process proceeds to method
step 314 wherein it is illustrated that the acquisition
failure (arising either from the inability to acquire the
carrier or the inability to acquire the pilot) is noted.
Thereafter, method step 316 shows that the CDMA carrier
frequency wherein pilot acquisition failed is added to
the list of failed channels contained within
CDMACH FAIL LIST.
Those skilled in the art will appreciate that in the
custom selection process depicted in method step 304 the
mobile subscriber unit's receiver is tuned to either the
primary or secondary channel in_order to subsequently
receive the CDMA channel list message. However, those
skilled in the art will also realize that CDMACHS (i.e.,
the frequency at which the mobile subscriber unit's
receiver is tuned) was reset in method stop 310 to the
channel upon which acquisition has failed. Since the
flow of the process depicted in Figure 3 re-enters the -
flowchart at a point in the flow below method step 304
(i.e., where CDMACHS is set to either the primary or
secondary channel "C"), it is necessary that a mechanism
exist to reset the CDMACHS to channel "C." Method step
318 illustrates that this mechanism is provided by the
CA 02287243 1999-10-13
WO 98/47238 PCT/US98/07433
24
variable CDMACHT~,,p wherein was stored the channel "C" in
method step 306; thus, CDMACHS can be thereafter utilized
as normal since subsequent to method step 318 CDMACHS will
be reset to the value of channel "C." Thereafter, the
process proceeds to method step 308 and proceeds as is
shown in the flow chart with it being understood that the
variables subsequently used in the flow will be those
necessary to modify the A~1SI J-STD-008 hash algorithm in
the manner chosen by the system designer.
In the event that the attempt to acquire the
selected carrier frequency/"pilot" channel as illustrated
in method step 3I2 was successful, the process proceeds
to method step 320 wherein it is depicted that the
successful acquisition of the pilot channel is noted.
Thereafter, the process proceeds to method step 322
wherein it is shown that the list of failed CDMA carrier
frequencies is reset to be empty (that is, since it is
possible that what was previously noted as a failed CDMA
carrier frequency may in fact become an operative carrier
frequency at some subsequent time, the list of failed
CDMA carrier frequencies is reset to empty upon every
successful CDMA carrier frequency/"pilot" channel
acquisition). Thereafter, the process proceeds to 324
wherein the mobile subscriber unit enters into the "Sync
Channel Acquisition Substate" as defined by ALtsI J-STD-
Q~ standard section 2.6.1.3.
It will be understood by those within the art that
the process illustrated in Figure 3 is to be re-engaged
in each time the mobile subscriber unit leaves the "Sync
Channel Acquisition Substate" and enters into a state
wherein it is necessary to acquire a new CDMA carrier
frequency upon which to communicate.
CA 02287243 1999-10-13
WO 98147238
PCTIUS98107433
Refer now to Figure 4. Figure 4 is a high-level
logic flow chart which depicts a method by-which another
_ embodiment of the present invention is able to alleviate
the foregoing described problem of Figure 2. The high-
level logic flow chart of Figure 4 can be referenced
specifically to the Is-95-A+TSH74 standard via the IS95
A+TSB74 standard section numbers depicted in Figure 4
(e.g.. 6.1.1, 6.1.1.1.1, 6.6.2.2.4, 6.6.7, 6.6.1.2, and
6.6.1.3). That is, the high-level logic flow chart
depicted in Figure 4 is intended to be used within the
context of IS-95-A+TSB74 systems to alleviate the
foregoing noted problems extant within the standard.
Method step 400 depicts the start of the process.
Method step 402 illustrates the event of "power up,"
which is essentially the event of turning on or bringing
online a mobile subscriber unit. Method step 404 shows
the initialization of a list of inoperative CDMA carrier
frequencies to be empty; that is, the variable
CDMACH FAIL LIST is set equal to NULL.
Subsequent to the setting of the list of inoperative
CDMA carrier frequencies (e.g., the setting of the
variable CDMACH FAIL LIST? method step 406 depicts the
engagement in the custom selection of a CDMA primary or
secondary channel as dictated by IS-95-A+TSB74 sections
6.6.1.1 and section 6.1.1.1.1. Thereafter, method step
408 depicts the determination of whether the custom
selection procedure of method step 406 resulted in an
acquisition failure. In the event that no acquisition
failure occurred. the process proceeds to method step 410
which illustrates that operation is to proceed as normal
under the current IS-95-A+TSB74 standard.
CA 02287243 1999-10-13
WO 98147238 PCT/US98/07433
26
In the event that an acquisition failure did occur,
the process proceeds to method step 412 which shows the
receipt of the list of CDMA carrier frequencies via a
CDMA Channel List Message in the fashion dictated by the
IS-95-A+TSB74 standard section 6.6.2.2.4. Thereafter, the
process proceeds to method step 414 wherein it is
depicted that a modified IS-95-A+TSB74 section 6.6.7 hash
algorithm is utilized to select a CDMA carrier frequency
such that the CDMA carrier frequency selected is not one
already noted to be inoperative. How such hash algorithm
can be modified to insure that the CDMA carrier frequency
selected is not one already noted to be inoperative has
been discussed above in reference to method step 310, and
such discussion is herein incorporated by reference in
its entirety. However, it is to be understood that in
the method shown in Figure 4 the variable CDMACHS is
utilized to indicate the channel selected by the modified
hash algorithm and to which the mobile subscriber unit's
receiver is thereafter tuned.
Method step 416 illustrates that subsequent to the
selection of a CDMA carrier frequency a determination is
made as to whether or not the selected CDMA carrier
frequency or the "pilot" channel within the selected CDMA
carrier frequency can be acquired. In the event that it
is determined that the "pilot" channel cannot be
acquired, the process proceeds to method step 418 wherein
it is shown that the acquisition failure is noted.
Subsequently, the process proceeds to method step 420
wherein it is depicted that the CDMA carrier frequency
for which CDMA carrier frequency/"pilot" channel
acquisition failed is added to the List of failed, or
inoperative, CDMA carrier frequencies; that is, variable
CDMACH-FAIL LIST is reset such that the failed, or
inoperative, channel is now included in the list of
CA 02287243 1999-10-13
WO 98147238 PCT/US98/07433
27
failed channels. Thereafter, the process returns to
method step 406 and proceeds from that point, utilizing
the adjusted inoperative channel list contained within
the variable CDMACH FAIL LIST.
In the event that it is determined that the "pilot"
channel can be'acquired, the process proceeds to method I
step 422 which illustrates that the acquisition success
is noted. Subsequently, the process proceeds to method
step 424 which shows that the list of inoperative
channels is reset to be empty; that is, the variable
CDMACH_FAIL LIST is reset to be NULL. Thereafter, the
process proceeds to the "Sync Channel Acquisition
Substate" defined by IS-95-A+TSB74 standard section
6.6.1.3.
It will be understood by those within the art that
the process illustrated in Figure 4 is to be re-engaged
in each time the mobile subscriber unit leaves the "Sync
Channel Acquisition Substate" and enters a state wherein
it is necessary to acquire a new CDMA carrier frequency
upon which to communicate.
While the invention has been shown and described
with reference to particular embodiments thereof, it will
be understood by those skilled in the art that the
foregoing and other changes in form and detail may be
made therein without departing from the spirit and scope
of the invention, which is defined only by the following
claims.
