METHOD FOR REDUCING CONTROL
CHANNEL SCAN TIME
FIELD OF INVENTION
The present invention relates generally to the communications field and, in particular, to a method for reducing the amount of time and resources required for a mobile unit to find an appropriate communications control channel in wireless communications systems.
BACKGROUND OF THE INVENTION
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 such 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.
During use, it is common for the mobile unit to initiate a band scan in order to locate an appropriate control channel. The band scan is a process by which a mobile unit searches through channels in a channel band, looking for an appropriate control channel to camp on. A band scan could be initiated for a wide variety of reasons, including at powerup, at call release, or when a control channel is lost. In some instances, multiple band scans are run back-to-back on different channel bands in what is called a wide-band scan. Because the band scanning process takes time and otherwise utilizes system resources including mobile unit power, it is very desirable for the band scan or wide-band scan to happen as quickly as possible.
SUMMARY OF THE INVENTION
The present invention is an improved method for a mobile unit to locate appropriate control channels in a wireless communications system, such as a cellular telephone system, operating on a communications spectrum having channel bands. The method is an improved band scan method which includes storing a list of acceptable service providers in the mobile unit, receiving service provider information identifying the service provider for a particular control channel, receiving minimum acceptable signal strength information for the control channel, determining the acceptability of the service provider by comparing the
received service provider information against the acceptable service provider list, and, if the service provider is acceptable, comparing the received signal strength for the control channel against the minimum acceptable level. If the
5 control channel is suitable, i.e. has sufficient received signal strength, and is allocated to an acceptable service provider, the mobile unit camps on the control channel. If the control channel is allocated to an unacceptable service provider, the mobile unit stores the received service provider information,
10 the channel number, and the channel band and then returns to the band scan invoking procedure. By checking the service provider information early, the method allows for the checking of received signal strength against the minimum acceptable level to be deferred or avoided. Thus, the method
15 reduces the time required to locate appropriate control channels in some situations and otherwise increases the efficiency of control channel scanning. The method is particularly useful in IS-136 cellular telephone systems.
20 BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a simplified representation of a cellular telephone wireless communications system.
FIG. 2 is an example of a typical communications spec
, trum organization showing channel bands.
25 6 6
FIG. 3 is a simplified logic flow diagram of the prior art. FIG. 3Ais a simplified logic flow diagram of the prior art showing a channel pointer trace process.
FIG. 4 is a simplified logic flow diagram of the present 30 invention.
FIG. 4A is a simplified logic flow diagram of the present invention showing a modified channel pointer trace process.
DETAILED DESCRIPTION OF THE 35 PREFERRED EMBODIMENT
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
4Q centers 16 connecting the wireless communications system
10 to other communications systems 18, such as the public
switched telephone network (see FIG. 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. 45 6
The radio links 13 typically include numerous discrete
communications channels 20 on one or more communications spectrums 50 (see FIG. 2). A communications channel 20 is typically a pair of frequencies, one transmit and one
50 receive, used by a mobile unit 12 to communicate within a wireless communications system 10. Some communications channels 20 are for control functions (control channels) while others are for voice and data communications (traffic channels). Examples of control functions include locating a
55 particular mobile unit 12, establishing a new communications session, and transferring oversight of a communications session from one base station 14 to another.
A wireless communications system 10 may utilize more than one communications spectrum 50. For instance, one
go spectrum 50 may be in the 800-900 MHz range while another may be in the 1850-2000 MHz range. For simplicity, the following description will discuss only one spectrum 50, but it is to be understood that the invention also includes the use of multiple spectrums 50.
65 A plurality of communications service providers typically compete in providing wireless communications service on a particular communications spectrum 50. It is customary for