Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1998-02-19
2002-06-04
Maung, Nay (Department: 2681)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S419000, C455S558000
Reexamination Certificate
active
06400948
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to systems and methods for allowing radiotelephones to acquire a control channel and, more particularly, to systems and methods for acquiring a control channel for selectively setting the number of entries in a history list, the content for the entries in the history list, and a threshold power level for a control channel.
BACKGROUND OF THE INVENTION
A mobile radiotelephone system includes a base station serving one or more cells and a plurality of radiotelephones, which are commonly mobile radiotelephones or mobile stations. The radiotelephones communicate with the base station through two different types of channels. The first channel is a voice channel and is used to carry voice and other transmissions between the radiotelephone and a base station. The other type of channel is a control channel and is generally used by the radiotelephone in acquiring a voice channel and in obtaining other service from the base station. For instance, control channels are used by a radiotelephone to select a particular cell within a radiotelephone network and to acquire a voice channel. The control channels are also used for various other purposes.
In the United States, the predominate radiotelephone system for mobile radiotelephones, or cellular phones, is the Advanced Mobile Phone System (AMPS). AMPS is an analog cellular system deployed nationwide and currently uses a common set of 21 analog control channels from which a mobile radiotelephone can obtain service, receive pages for incoming calls, and originate outgoing calls. In general, the bandwidth available for AMPS is divided into an A-Band and a B-Band with these two bands being serviced by two different carriers. The A-Band has a range of channels in the 313 to 333 MHz bandwidth and the B-Band has a set of channels in the 334 to 354 MHz bandwidth. A mobile radiotelephone will typically be set for either the A-Band or the B-Band depending upon its carrier. Because of the fairly limited number of control channels in AMPS, a mobile radiotelephone can always ensure that a scan through these channels should result in finding an appropriate channel through which service may be obtained. If no channels are found, then the radiotelephone may assume that there is no service in the current area but continue to search periodically.
A new generation of mobile radio telephones is reflected in Telecommunications Industry Association (TIA) standard EIA/TIA IS-136. IS-136 capable mobile radiotelephones transmit and receive digital signals which have been multiplexed together in a time division multiple access (TDMA) system. These digital mobile radiotelephones offer a number of features not found in the pure analog mobile radiotelephones, such as short message service (SMS), voice and data privacy, a message waiting indicator (MWI), calling number identification (CNI), and circuit-switched data support. IS-136 capable digital phones are designed to operate both in the analog spectrum as well as in the purely digital spectrum of the 1900 MHz frequency bands. They provide seamless operation on both the AMPS analog cellular system as well as an IS-136 system.
A core component of the EIA/TIA standard IS-136 is the definition of a digital control channel (DCCH). The DCCH is a new control channel added to existing analog control channels (ACCs), analog voice channels (AVCs), and the digital traffic channels (DTCs) of a TDMA system. The DCCH enables many of the new functions and enhanced features of IS-136. In contrast to analog control channels, the DCCH may be placed on any channel in the frequency range of the mobile radiotelephone system and a radiotelephone network may offer a greater or lesser number of DCCHs than ACCs.
The detection and acquisition of a DCCH, however, is not as easy as the acquisition and detection of an ACC. As discussed above, the AMPS cellular network typically has twenty one control channels with these control channels being set at predefined frequencies. An AMPS cellular phone can quickly scan through the twenty one frequencies to find an ACC through which cellular service may be obtained. In contrast to an ACC, the DCCH may be located at any channel within the frequency range of the cellular carrier. Cellular networks, furthermore, may have differing numbers of DCCHs, with one network possibly having twenty one DCCHs while another neighboring network having thirty three DCCHs. Due to the uncertain number of DCCHs and their uncertain location within the available bandwidth, an IS-136 capable phone cannot quickly or easily perform a scan of the bandwidth to locate a suitable DCCH.
In light of the difficulty of scanning a multitude of channels in order to obtain cellular service, IS-136 phones are commonly provided with a “history list” of channels. The history list is generated by the digital phone dynamically as the phone operates in a cellular environment. Typically, cellular carriers will utilize a common set of channels system-wide in which to place their DCCHs. A digital phone will build its history list of DCCHs by placing on the list those DCCHs through which the phone has obtained service with the first position on the list designated for the DCCH used most recently. When a digital phone attempts to locate a DCCH, the digital phone scans the entire list and removes from consideration those channels below a minimum threshold power level. Of the channels above the threshold, the radiotelephone selects the strongest channel available. A history list could theoretically contain any number of channels which the phone will scan for service, but a balance of the number of channels, the amount of time required to scan them, and the amount of memory required to store them will, as a practical matter, limit the number of DCCHs stored in the history list.
The factors of the time required to scan the channels and the maximum number of channels allowed in memory can greatly affect the performance of a digital cellular phone in a specific cellular network. For example, a digital cellular phone that stores only five channels in its history list operating in a system where the carrier has chosen to use twenty different DCCH channels for reuse across the system will only be effective at best five out of twenty different times. The five channels stored in the phone will preferably be channels that the user has acquired service on previously via different methods whereby the use of these five channels increases the user's chance that one of them will be available. Nonetheless, by increasing the number of DCCHs stored in the history list, the digital phone increases its chances that it will find an available DCCH. For instance, if a digital phone increases the number of DCCHs stored in its history list from five to ten, then the odds that an available DCCH will be found is increased from approximately five out of twenty times to ten out of twenty times.
The structuring of the history list so that it contains the most recently used channels is not without its shortcomings. This type of history list works well when the user stays within commonly used cells of a cellular network or stays within just one cellular network. When the user enters other cells of the cellular network or enters another cellular network, the location of the DCCHs in these other cells or in this other network may be different from the locations of the DCCH for the cells within which the user typically travels. As a result, when the IS-136 capable phone attempts to locate a DCCH in one of these other cells or in another network, the IS-136 capable phone will likely find it difficult to obtain service using the DCCHs stored in its history list. The history list therefore provides its optimal functionality only when the user limits his or her movement to within a limited number of regularly used cells.
In addition to the problem of the uncertain locations of the DCCHs, a cellular carrier in one network may have a larger number of control channels than a cellular carrier in another network. For instance, o
BellSouth Intellectual Property Corporation
Kilpatrick Stockton, Esq.
Maung Nay
Sutcliffe, Esq. Geoff L.
Wang, Esq. Li K.
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