WO1999022540A1

WO1999022540A1 - Avoiding forbidden service provider control channels during reselection

Info

Publication number: WO1999022540A1
Application number: PCT/US1998/021831
Authority: WO
Inventors: Richard M. Abdella
Original assignee: Ericsson Inc; Ericsson GE Mobile Communications Holding Inc
Current assignee: Ericsson Inc
Priority date: 1997-10-29
Filing date: 1998-10-15
Publication date: 1999-05-06
Anticipated expiration: 2000-04-29
Also published as: AU1091599A

Abstract

A method for avoiding control channels belonging to forbidden service providers during reselection in a wireless communications system includes checking the service provider of candidate control channels and setting a candidate ineligibility flag if the service provider is from a forbidden class. When reselection is triggered, due to the mere passage of time or some other condition, a neighbor list of control channels is filtered based on received signal strengths to create a viable neighbor list (VNL) of viable candidatae control channels. Each time a candidate control channel is selected from the viable neighbor list for examination, the service provider for the candidate control channel is identified. If the service provider is from a forbidden class, a candidate ineligibility flag is set for that control channel, and the channel is not camped on. Preferably, the candidate control channel is not examined further after the candidate ineligibility flag is set. If the candidate control channel fails, due to forbidden service provider, signal characteristics, or other factors, another candidate control channel is selected for examination from the viable neighbor list. In this manner, the mobile unit is prevented from camping on a control channel belonging to a forbidden service provider during reselection.

Description

AVOIDING FORBIDDEN SERVICE PROVIDER CONTROL CHANNELS DURING

RESELECTION

FIELD OF INVENTION

The present invention relates generally to the communications field and, in

particular, to a method for avoiding a forbidden service provider's control channels

during reselection in wireless communications systems.

BACKGROUND

Wireless communication systems, such as cellular telephone systems, have

proved to be very popular. Such systems typically include numerous mobile units

(e.g., cellular telephones), a plurality of base stations at fixed locations, and one or

more switching centers connecting the wireless communication systems to other

communications systems, such as the land line public switched telephone network.

It is common for wireless communications systems to employ a large

number of discrete communication channels for communicating voice and data

from one location to another and for controlling system functions. It is also

common for there to be multiple communications service providers in competition

with each other for each type of communication service. Further, within a given

geographical area, it is typical for the various communication channels to be

allocated to the different competitors such that only one service provider is

responsible for providing service on any given channel.

To facilitate communications channel allocation, the spectrum of channels

may be divided into several channel bands, each containing a plurality of

communications channels. Thereafter, an entire channel band is typically allocated to a particular service provider for a given geographic region. Thus, in a certain

region, service provider Alpha may be allocated channel bands A and C, while

service provider Beta may be allocated channel band B, and service provider

Gamma all other channel bands. The particular details of the channel band

allocations are well known in the industry.

The various service providers are typically in competition with each other.

However, many service providers have bi-lateral agreements under which

subscribers (users) to one service provider may use the communications network

of another service provider. Despite the prevalence of such agreements, some

service providers have no such agreements with particular other service providers

for competitive reasons. For example, service provider Alpha may have a sharing

agreement with service provider Beta, but no agreement with service provider

Gamma. Users who are subscribed to Alpha may use communications channels

belonging to service provider Beta, but should not use any channels belonging to

service provider Gamma. In order to ensure this, the Alpha mobile units are

typically given a list of service providers that are forbidden to be used; in this

example, the list would include Gamma but not Beta.

When a mobile unit is roaming, it is desirable for the mobile unit to use

certain service providers and avoid others. For instance, it may be desirable for

the mobile unit to use service providers Alpha and Beta, but completely avoid

forbidden service providers such as Gamma. Intelligent roaming allows this to

happen. In intelligent roaming, the mobile unit considers the identity or

classification of the service provider when selecting service. The methods and

protocols for intelligent roaming contain substantial safeguards, well known in the art, to ensure that the mobile unit obtains service from more desirable service

providers and avoids forbidden ones. One of the primary goals of intelligent

roaming is managing the provision of communications services from the various

service providers, and particularly preventing service acquisition on forbidden

service providers except in emergencies.

However, the existing intelligent roaming protocols have not been fully

developed and it is possible under some non-emergency circumstances that the

mobile unit may use a control channel belonging to a forbidden service provider.

One such circumstance is during control channel reselection.

While camped on one control channel, it is common for the mobile unit to

periodically attempt to obtain better service on a different control channel. If the

mobile unit finds a better control channel, the mobile unit will switch to that channel.

This process is called control channel reselection, or simply reselection.

Reselection is very helpful in optimizing service.

In addition to being a periodic event, reselection may also be a triggered

event. Several conditions may trigger reselection. For instance, signal conditions

on the control channel may cause the wireless communications system, or the

mobile unit itself, to initiate reselection. Alternatively, the wireless communications

system may cause the mobile unit to enter reselection by creating a cell barred

condition or by sending a directed retry message. In such situations, reselection is

triggered because the current control channel is somehow deficient. Whether

reselection is triggered by the mere passage of time or by some other condition,

the goal of reselection is to find another acceptable control channel, preferably one

that is better than the current control channel. However, in some situations, reselection may undermine the goal of

intelligent roaming and result in service acquisition on a forbidden service provider.

For instance, it is possible that the "best" control channel identified during

reselection will belong to a forbidden service provider. Because the prior art

reselection methods did not check the service provider classification, the mobile

unit would simply proceed to camp on this control channel. As a result, a mobile

unit programmed to avoid a particular service provider could end up using that

forbidden service provider, thereby defeating the intent of intelligent roaming.

Accordingly, there exists a need for method of identifying and then avoiding

control channels belonging to forbidden service providers during reselection in

wireless communications systems.

SUMMARY OF THE INVENTION

The present invention provides a method for identifying and then avoiding

control channels belonging to forbidden service providers during reselection. A

wireless communications system mobile unit is provided with a list of forbidden

service providers. When the mobile unit is camped on a control channel, the

wireless communications system sends the mobile unit a neighbor list (NL) of

potential candidate control channels. The mobile unit then monitors the received

signal strength of those channels. Thereafter, when a reselection is triggered, due

to the mere passage of time or some other condition, the neighbor list is filtered

based on at least the received signal strength to create a viable neighbor list (VNL)

of viable candidate control channels. A candidate control channel, called CAND_1 ,

is selected from the viable neighbor list and more thoroughly examined. As part of

this examination, the service provider for the candidate control channel is identified. If the service provider is from a forbidden class, i.e., is a Forbidden SP, a candidate

ineligibility flag is set for that control channel, and the channel is not camped on.

Preferably, the candidate control channel is not examined further after the

candidate ineligibility flag is set. If the candidate control channel fails, due to

forbidden service provider, signal characteristics, or other factors, another

candidate control channel is selected for examination from the viable neighbor list.

The method also preferably checks the candidate ineligibility flag during the filtering

of the NL to the VNL and during the selection of the candidate control channel from

the VNL. In this manner, the mobile unit is prevented from camping on a control

channel belonging to a forbidden service provider during reselection.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGURE 1 is a simplified representation of a cellular telephone wireless

communications system.

FIGURE 2 is a simplified logic flow diagram of the overall reselection

process.

FIGURE 3 is a simplified logic flow diagram of the filtering portion of the

present reselection method.

FIGURE 4 is a simplified logic flow diagram of the examination portion of the

present reselection method.

DETAILED DESCRIPTION

A wireless communications system 10 typically includes numerous mobile

units 12 (e.g., cellular telephones), a plurality of base stations 14, and one or more

switching centers 16 connecting the wireless communications system 10 to other

communications systems 18, such as the public switched telephone network (see Figure 1). Typically, the mobile units 12 communicate with the base stations 14

using radio links 13. Likewise, the base stations 14 typically communicate with the

switching center 16 via radio links 15.

The radio links 13 typically include numerous discrete communications

channels on one or more communications spectrums. A communications channel

is typically a pair of frequencies, one transmit and one receive, used by a mobile

unit 12 to communicate within a wireless communications system 10. Some

communications channels are for control functions (control channels) while others

are for voice and data communications (traffic channels). Examples of control

functions include locating a particular mobile unit 12, establishing a new

communications session, and transferring oversight of a communications session

from one base station 14 to another.

For any given communications service, there are typically a number of

service providers competing to provide the service in a given area. To provide

some order to the marketplace, the communications channels are usually allocated

to the various competing communications service providers. Typically this

allocation is in groups of communications channels known as channel bands. In a

particular geographic area, only one service provider will provide service on any

given channel. However, other service providers may provide competing service

on different channels. Thus, at any given location, a mobile unit 12 may be within

the service area of a plurality of different service providers operating on different

channels.

For a particular mobile unit 12, the various service providers may be

classified as either a Home SP, a Partner SP, a Favored SP, a Neutral SP, or a Forbidden SP. When acquiring service on a control channel, the mobile unit 12 will

scan the available control channels and make a selection based on the service

provider classification. Home SPs and Partner SPs are preferred over all others

and are known as acceptable service providers. A Favored SP has a lower priority

than an acceptable SP, but a higher priority than a Neutral SP. The lowest

classification is Forbidden SP. The mobile unit 12 will not register with a Forbidden

SP except in emergencies, such as when "911" is dialed. As used herein, the

term "Forbidden SP" refers to a service provider that should be used for

communications only in emergencies. The mobile unit 12 should acquire service

on a control channel with the highest classification level.

It is common in wireless communications systems 10 for mobile units 12 to

contain a programmable Intelligent Roaming Database (IRDB). The IRDB typically

includes a listing of service provider identification codes, including a listing of

Forbidden SP identification codes, a band search list, and various other control

information. The identification codes used by the IRDB typically are system ID's

(SID) and/or system operator codes (SOC).

The IRDB is commonly stored in semi-permanent memory in the mobile unit

12. That is, the IRDB is stored in the mobile unit 12 even while the mobile unit 12

is not in use, but the contents of the IRDB can be changed by the wireless

communications system 10, possibly through over-the-air programming, or by an

authorized technician. The mobile unit 12 user is typically not able to program the

IRDB independently.

In practice, the IRDB is usually supplemented by the Number Assignment

Module (NAM). The NAM is programmable memory containing specific information about a mobile unit 12 such as the electronic serial number, phone number, and

the like. Like the IRDB, the NAM is semi-permanent memory. However, it should

be noted that the electronic serial number portion of the NAM is typically only

programmable by the mobile unit's 12 manufacturer due to "cloning" concerns.

The NAM also contains the identification code for the mobile unit's 12 Home SP.

For simplicity of discussion, the NAM will be considered part of the IRDB.

An idle, but active mobile unit 12 typically camps on a control channel while

waiting for a page or call activation command. While camped on one control

channel, it is common for the mobile unit to periodically attempt to obtain better

service on a different control channel. If the mobile unit finds a better control

channel, the mobile unit will switch to that channel. This process is called control

channel reselection, or simply reselection.

In addition to being a periodic event, reselection may also be a triggered

on the control channel may cause the wireless communications system, or the

system may cause the mobile unit to enter reselection by creating a cell barred

triggered because the current control channel is somehow deficient.

Whether reselection is triggered by the mere passage of time or by some

other condition, the goal of reselection is to find another acceptable control

channel, preferably one that is better than the current control channel, without

going through the entire initial selection routine. The acceptability of the new

control channel is based on a several selection criteria which are in turn dependent on the triggering condition. The interplay of the trigger condition and the selection

criteria is well known in the art. For simplicity, the following discussion will use a

reselection procedure triggered by the mere passage of time (periodic reselection)

for illustrative purposes; however, the method of the present invention is applicable

to and includes reselections triggered by other conditions.

In a broad sense, reselection is accomplished by checking a list of candidate

control channels to determine if any of those channels would offer better service. If

so, the mobile unit switches to that better control channel; if not, the mobile unit

remains camped on the current control channel. Ideally, reselection results in the

mobile unit 12 locating the "best" available control channel as quickly as possible

and switching to that control channel.

Once a mobile unit is registered with a wireless communications system and

is camped on a control channel, the mobile unit receives a list of potential

alternative control channels called a Neighbor List (NL). In systems operating

according to the protocols described in Telecommunications Industry Association

Interim Standard IS-136, the NL is received as part of an E-BCCH message. In

practice, the NL can be supplemented by potential alternative control channels

identified by Private Operating Frequencies (POFs) and Non-Public Mode Search

(NPS-DCCH). For simplicity of discussion, these potential alternative control

channels will be considered part of the NL. The mobile unit monitors the NL

channels for signal strength when the mobile unit is not busy performing other

tasks and stores their respective received signal strengths (RSSI) measurements.

Preferably, the mobile unit keeps a running average of the respective RSSI

measurements, such as for the last five RSSI measurements. The reselection process includes three main steps: filtering the NL,

determining which is the best candidate control channel, and examining that control

channel. Filtering involves creating a Viable Neighbor List (VNL) which is a sub-list

of the NL comprised of potential alternate control channels that meet certain

criteria. The particular criteria used to filter to the NL to the VNL depends on what

condition triggered the reselection, but typically includes RSSI. This filtering

process is well known in the art, and a detailed discussion is not necessary to

understanding the present invention.

During the filtering process, some ineligibility status flags are checked, and

may be used to prevent the associated potential alternate control channels from

being added to the Viable Neighbor List. Examples of such ineligibility status flags

include temporary ineligible for reselection (TIR) and ineligible for service offering

reasons (ISOR).

Once the VNL is established, the reselection process proceeds in a looping

two-step process: selecting the best candidate control channel from the VNL and

then checking that candidate in more detail. In the first step, called CAND_1

Determination, the best candidate control channel from the VNL is identified and

labeled as CAND_1. In the second step, called CAND_1 Examination, the

CAND_1 control channel is more thoroughly checked for appropriateness. If

CAND_1 is inappropriate, that candidate is marked with an ineligibility flag, and the

process returns to CAND_1 Determination to find the best of the remaining

candidates. Reselection loops through these steps until there are no more

candidates on the VNL. If one of the candidates is found to be better than the

current control channel, the mobile unit switches to that control channel. The details of CAND_1 Determination and CAND_1 Examination are well

known in the art and a complete discussion is not necessary for understanding the

present invention. However, it should be noted that during CAND_1 Determination,

ineligibility status flags, such as TIR and ISOR, are used to prevent control

channels from becoming CAND_1. Further, the TIR and ISOR ineligibility status

flags may be set during CAND_1 Examination depending on the results of

evaluation.

In the prior art reselection process, the classification of the candidate control

channel's service provider is not checked or otherwise used to evaluate the

candidate control channels. Unfortunately, it is possible that a control channel

allocated to a Forbidden SP may be included on the NL. As such, it is possible that

the mobile unit operating under the prior art may conclude the reselection process

by camping on a control channel allocated to a Forbidden SP.

For instance, assume service provider Beta has a bi-lateral sharing

agreement with service providers Alpha and Gamma. However, Alpha and Gamma

are competitor service providers which have no agreement between themselves

and consider each other as Forbidden SP. If an Alpha mobile unit 12 is in an area

served by Beta, it may have been sent a NL by service provider Beta. Because

Beta has an agreement with Gamma, this NL may include some Gamma control

channels. If one of the Gamma control channels has the best signal

characteristics, etc., of the candidates on the NL (and the current control channel)

the prior art reselection process would conclude with the Alpha mobile unit

camping on the Gamma control channel. Thus, under the prior art, the Alpha

mobile unit 12 might start on an acceptable service provider's (Beta) control channel, but end up on a Forbidden SP's (Gamma) service channel after

reselection. This defeats the intent of intelligent roaming.

The reselection method of the present invention checks the service provider

classification as part of candidate evaluation and utilizes a new ineligibility status

flag to mark those control channels which are allocated to Forbidden SP.

The candidate eligibility filtering of the present invention is shown in Figure 2

and includes three main steps: filtering the NL (box 200), determining which is the

best candidate control channel (box 300), and examining that control channel (box

400).

Filtering (box 200) includes evaluating potential candidate control channels

from the Neighbor List against various criteria to produce a Viable Neighbor List. In

addition to the evaluation criteria of the prior art, the present invention checks a

new ineligibility status flag called Carryover Ineligibility (Cl). Cl is a status flag that

indicates whether the particular control channel has already been determined to be

allocated to a Forbidden SP. The setting of this flag is described below. Unlike the

TIR flag, which may be reset at the beginning of each reselection, or the ISOR flag,

which may be reset after a pre-determined period of time, once set, the Cl flag is

not reset until a new NL is received.

Filtering (box 200) begins by retrieving the NL and associated RSSI

measurements (box 210). See Figure 3. Any ineligibility status flags are retrieved

when the NL is retrieved. Then, starting with the first potential alternate control

channel on the NL (box 220), the Cl flag of the candidate is checked (box 230). If

the Cl flag is set (box 230), the eligibility filtering of the prior art (box 240) is

skipped for that candidate, the candidate is not added to the VNL, and the filtering process continues with the next potential alternate control channel on the NL

(boxes 270,280). If the Cl flag is not set (box 230), the process proceeds as with

the filtering of the prior art (box 240). If the candidate is eligible (box 250), the

candidate is added to the VNL (box 260). Then, the next candidate is evaluated

(box 270,280). When there are no more candidates on the NL (box 270), filtering

stops (box 290). In this manner, the VNL is built and candidate control channels

with Cl flags set are prevented from being added to the VNL.

As discussed above, the checking of the Cl flag (box 230) is preferably done

before the prior art filtering criteria are applied to evaluate the candidate (box 240).

Alternatively, the Cl flag may be checked at other times during filtering, or may not

be checked at all during filtering. For instance, the Cl flag may be checked when

the other ineligibility flags are checked.

Once the VNL is established, the reselection process of the present

invention enters a looping process of determining which is the best candidate

control channel from the VNL (box 300), checking that candidate in more detail

(box 400), and switching to the candidate (box 900) if it is better than the current

control channel (box 500), or moving to the next candidate (box 600) if it is not.

See Figure 2.

As with the prior art, during CAND_1 Determination (box 300), the best

candidate control channel from the VNL is identified and labeled as CAND_1.

Further, ineligibility status flags are checked during this step, but with the Cl flag

added to the list of possible ineligibility flags which prevent the respective

candidate control channel from becoming CAND_1. Referring now to Figure 4, once CAND_1 is selected, the service provider

classification for CAND_1 is checked (box 410). Preferably, this is accomplished

by decoding the F-BCCH message of the control channel. The F-BCCH is a logical

channel which is used to broadcast digital control channel (DCCH) structure

parameters and other information essential for accessing the wireless

communications system 10. In particular, encoded within the F-BCCH message, in

a manner well known in the art, are several parameters relating to service provider

identification. For typical IS-136 systems, these parameters include SID and,

optionally, SOC. Thereafter, the classification of the service provider for CAND_1

is checked by comparing the service provider information against the IRDB (box

410). If the service provider information indicates the CAND_1 belongs to a non-

forbidden SP, CAND_1 is examined as in the prior art (box 450).

If the service provider information indicates that CAND_1's service provider

is a Forbidden SP, the Cl flag for CAND_1 is set (box 420), the RSSI of CAND_1 is

optionally set to a very low value, such as -113 dBm (box^;430), and examination

process terminates.

After examining CAND_1 (box 400), reselection proceeds as in the prior art.

If CAND_1 is better than the current control channel (box 500), the mobile unit

camps on CAND_1 (box 900). If CAND_1 is not better than the current control

channel, the next candidate is selected (box 600).

It is preferred that CAND_1's service provider be checked (box 410) before

proceeding to Examination of the prior art (box 450). However, it is within the

scope of the present invention for this service provider checking, and the

associated Cl flag setting and optional RSSI setting, to be integrated with the prior art Examination (box 450). Alternatively, CAND-1's service provider checking (box

410) could be done later, but before the switching decision (box 500).

If none of the candidate control channels on the VNL are better than the

current control channel, the reselection process terminates by executing an

appropriate candidate not found procedure (CAND_NOT_FOUND procedure), well

known in the art (box 990).

It should be noted that the Cl flag is preferably checked (box 410) during

CAND_1 Determination (box 300) because CAND_1 Determination looks through

the entire VNL list for each pass and the Cl flag may be set for a particular

candidate control channel after the VNL is established.

In summary, the present method sets the Cl ineligibility flag (box 420) when

it is determined that the candidate control channel's service provider is a Forbidden

SP (box 410). If the Cl flag is set (box 230), the control channel will be filtered out

and prevented from being added to the VNL. Further, if the Cl flag is set (box 230),

the associated control channel cannot be selected as CAND_1. Because a control

channel must be CAND_1 before it can be switched to as a result of reselection,

the Cl flag prevents switching to control channels belonging to a Forbidden SP

during reselection.

The discussion above has focused on reselection triggered by the mere

passage of time. In such a scenario, the purpose of reselection is to find a better

control channel than the current control channel. If, on the other hand, reselection

has been triggered by other conditions, the purpose of reselection is to find an

acceptable control channel, not one that necessarily has better signal

characteristics than the current control channel, without going through the entire initial selection routine. That is, the determination of what is "better" (box 500) will

depend on a number of factors including, but not limited to, signal strength. The

weighting and interplay of these factors are well known in the art. In some

reselection situations, the current control channel will become essentially invalid,

meaning that almost all other candidate control channels will be "better" than the

current control channel. Accordingly, the meaning of "better" in box 500 may

understood to mean "acceptable" in some situations, as known in the art.

The present method helps further ensure that mobile units will not use

Forbidden SP's when roaming. Thus, the present method fills a gap in safeguards

of the prior art. By preventing use of Forbidden SPs, the present method helps

user satisfaction in wireless communications systems.

The description above has assumed that the wireless communications

system 10 is a IS-136 digital cellular telephone network; however, the present

reselection method also functions in other wireless communications environments

where there are multiple service providers, some of which are forbidden to

particular mobile units.

The discussion above has assumed that the initial control channel camped

on is a digital control channel. While the present invention also applies to analog

control channels, it is believed that reselection from analog control channels is

typically handled in a substantially different manner. For instance, in IS-136

systems, reselection from an analog control channel does not involve the use of a

neighbor list NL. However, those reselections from analog control channels

coming within the scope of the appended claims are intended to be encompassed

therein. Note that the candidate control channels may be either analog or digital. The discussion above has principally used a cellular mobile telephone as

the example of a mobile unit 12. However, it is to be understood that the present

invention encompasses any type of mobile unit 12, e.g., a cellular mobile

telephone, a pager, a personal communications device, or any other device that

uses a wireless communication system 10 having a plurality of service providers, at

least one of which is forbidden, and which uses channel pointers.

The present invention may, of course, be carried out in other specific ways

than those herein set forth without departing from the spirit and essential

characteristics of the invention. The present embodiments are, therefore, to be

considered in all respects as illustrative and not restrictive, and all changes coming

within the meaning and equivalency range of the appended claims are intended to

be embraced therein.

Claims

CLAIMSWhat Is Claimed Is:

1. A method for a wireless communications system mobile unit to avoid

camping on a control channel belonging to a forbidden service provider,

comprising:

a) camping on a first control channel;

b) thereafter triggering a reselection; said reselection including:

i) selecting a second control channel as a candidate control

channel;

ii) identifying the service provider for said candidate control

channel; and

iii) camping on a control channel other than said candidate

control channel if said service provider for said candidate control channel is from a

forbidden class.

2. The method of claim 1 wherein said reselection further includes setting a

candidate ineligibility flag associated with said candidate control channel after said

identifying if said service provider for said candidate control channel is from a

forbidden class.

3. The method of claim 2 further including storing said ineligibility flag with

said respective candidate control channel.

4. The method of claim 1 wherein said reselection further includes forming

a viable neighbor list before said selecting.

5. The method of claim 1 further comprising forming a neighbor list of

potential candidate control channels after said camping and before said triggering.

6. The method of clam 5 further comprising monitoring the received signal

strength of said potential candidate control channels.

7. The method of claim 6 wherein said reselection further includes filtering

said neighbor list to create a viable neighbor list of viable candidate control

channels based on said received signal strength of said potential candidate control

channels before said selecting.

8. The method of claim 7 wherein:

a) said reselection further includes setting a candidate ineligibility

flag associated with said candidate control channel after said identifying if said

service provider for said candidate control channel is from a forbidden class; and

b) said filtering includes checking said candidate ineligibility flag and

excluding any potential candidate control channels from said viable neighbor list

whose candidate ineligibility flag has been set.

9. The method of claim 1 wherein said first control channel is a digital

control channel.

10. The method of claim 1 wherein said second control channel is a digital

control channel.

11. The method of claim 1 wherein said second control channel is an analog

control channel.

12. The method of claim 1 wherein said identifying includes decoding a

F-BCCH message.

13. The method of claim 1 further comprising storing a list of forbidden

service providers in the mobile unit after said camping on a first control channel.

14. The method of claim 1 wherein said reselection further includes camping

on said candidate control channel if the service provider for said candidate control

channel is not from a forbidden class.

15. A method for a wireless communications system mobile unit to avoid

camping on a control channel belonging to a forbidden service provider,

comprising:

a) camping on a first control channel; wherein said first control

channel is a digital control channel;

b) storing a list of forbidden service providers in the mobile unit;

c) after said camping, forming a neighbor list of potential candidate

control channels and monitoring the received signal strength of said potential

candidate control channels;

d) thereafter triggering a reselection; said reselection including:

i) filtering said neighbor list to create a viable neighbor list of

viable candidate control channels based on said received' signal strength of said

potential candidate control channels;

ii) after filtering, selecting a second control channel as a

candidate control channel from said viable neighbor list;

iii) identifying the service provider for said candidate control

channel;

iv) thereafter setting a candidate ineligibility flag associated

with said candidate control channel if said service provider for said candidate

control channel is from a forbidden class; and v) thereafter camping on a control channel other than said

candidate control channel if said service provider for said candidate control channel

is from a forbidden class.

16. The method of claim 15 wherein filtering includes checking said

candidate ineligibility flag and excluding any potential candidate control channels

from said viable neighbor list whose candidate ineligibility flag has been set.

17. The method of claim 15 wherein said selecting includes excluding any

viable candidate control channels whose candidate ineligibility flag has been set.

18. The method of claim 15 wherein said identifying includes decoding a

F-BCCH message.

19. The method of claim 15 wherein said reselection further includes

camping on said candidate control channel if the service provider for said

candidate control channel is not from a forbidden class.

20. The method of claim 15 wherein said reselection further includes storing

said ineligibility flag with said respective candidate control channel.