Telecommunications – Transmitter and receiver at same station – Radiotelephone equipment detail
Reexamination Certificate
1998-12-21
2002-09-24
Le, Thanh Cong (Department: 2684)
Telecommunications
Transmitter and receiver at same station
Radiotelephone equipment detail
C455S439000, C455S552100, C455S553100, C370S229000, C370S331000, C370S332000, C370S333000
Reexamination Certificate
active
06456858
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to wireless networks, more specifically to dual-mode wireless telephone communication networks that overlay digital cellular systems over existing analog-based cellular systems.
2. Background Art
Wireless telephone communication systems have evolved from the Advanced Mobile Phone Service (AMPS) technology, introduced around 1983, to more sophisticated digital-based air interface protocols. Specifically, the AMPS technology is an analog-based technology that uses frequency division multiple access techniques to divide the available radio spectrum into channel bandwidths, where each 30 kilohertz voice channel supports a single conversation. The AMPS system includes a plurality of base stations transmitting voice channels within the 800 MHz cellular band into overlapping propagation regions, also referred to as cells, to establish a cellular-based coverage area.
Digital access technologies have been developed based on Time Division Multiple Access (TDMA) or Code Division Multiple Access (CDMA) schemes. These digital access technologies are more efficient relative to analog-based access technologies such as AMPS. In TDMA, the RF carrier is divided into time slots. The digital system allocates speech to these time slots by converting and compressing speech information carried by analog voice signals into compressed digital samples using vocoding techniques, enabling the speech samples to fit into the time slots. Hence, 3 or more time slots may fit into each 30 kHz channel, resulting in at least a three-fold increase in capacity. The well-recognized TDMA-based GSM standard utilizes 8 time slots in 200 kHz bandwidth channels.
Code Division Multiple Access (CDMA) is an even more efficient access technology, where the compressed speech samples are spread over a large frequency band by coding each speech sample with a unique pseudorandom sequence. Multiple voice samples can then be sent through the same wide-frequency band. The digital wireless telephone having the correct pseudorandom sequence will reproduce the corresponding speech sample, whereas voice samples transmitted with different pseudorandom sequences will appear as background noise in the frequency band.
Hence, digital access technologies have substantial advantages over analog-based systems. Digital cellular systems, however, have not yet been deployed in as many regions as AMPS-based systems. Hence, digital cellular subscribers are offered continuous coverage using dual-mode wireless telephones capable of switching between a first mode (e.g., CDMA) and a second mode (e.g., AMPS) based on the availability of a certain technology.
Current dual-mode digital telephones are configured for initially searching for the preferred and digital technology, such as CDMA. Hence, the dual-mode wireless telephones will connect to an alternative technology (e.g., AMPS) only if the dual-mode digital telephone is unable to establish a link with the preferred digital (e.g., CDMA) technology. Hence, the dual-mode telephone will always try to look for the preferred CDMA technology first.
One problem encountered in digital cellular systems is that the digital wireless communication system may encounter a traffic condition that results in a system overload in the digital wireless communication system. For example, the number of CDMA telephone users may exceed a certain number that results in an unacceptably high level of system noise in the common air interface, also referred to as the airlink interface. Alternatively, atmospheric conditions may cause interference overload of the airlink. Alternatively, a hardware failure in a base station or within the switching matrix of the digital wireless communication system may reduce the capacity of the digital wireless communication system, resulting in system blockage on the digital wireless communication system.
One possible solution to overcoming the blockage problem in the digital wireless communication system is to transfer an existing telephone call by a dual-mode telephone from the CDMA-based system to the alternative AMPS-based system using a hard handoff protocol. The hard handoff from the CDMA-based system within the dual-mode system to the AMPS-based system is one of the most complicated and signaling-intensive procedures in wireless networks, especially since the dual-mode wireless telephone must switch from the digital mode to analog mode simultaneously with the hard handoff. Hence the hard handoff from the CDMA system to the AMPS system has a substantial risk in dropping the call.
In addition, attempts to transfer a CDMA-based wireless telephone call initiated by dual-mode telephone to an analog system requires the dual-mode telephone and the analog-based AMPS system to effectively reinitiate the telephone call before the calls go through, resulting in a substantially long time for call completion when a dual-mode wireless telephone user places a call.
SUMMARY OF THE INVENTION
There is a need for an arrangement that minimizes the occurrence of a dropped call and minimizes call setup time by a dual-mode telephone in a dual-mode digital cellular system encountering traffic or overload conditions.
There is also a need for an arrangement that enables a dual-mode telephone system to redirect dual-mode telephones to access an alternative wireless telephone system based on detected traffic conditions in the digital wireless communication system.
These and other needs are attained by the present invention, where a dual-mode wireless communications system, having a digital wireless communications system and a second wireless communications system, selectively outputs a control command from the digital wireless communications system to at least one selected dual-mode wireless telephone based on a detected traffic condition in the digital wireless communication system. The control command, output to a selected dual-mode wireless mode telephone having registered with the digital wireless communication system, instructs the selected dual-mode wireless telephone to register with the second wireless communication system, for example when the dual-mode wireless telephone is in an idle state. Hence, the digital wireless communication system can selectively limit access by the dual-mode digital telephones by outputting a control command to selected dual-mode telephones to register with the second wireless communication system. Consequently, dual-mode telephones can be proactively configured to access the alternative wireless communication system during detected traffic conditions in the digital wireless communication system, avoiding any handoff or registration steps that normally would be encountered upon initiating a wireless telephone call on the digital wireless communication system.
According to one aspect of the present invention, a method is provided in a dual-mode wireless communication system having a digital wireless communication system overlying a second wireless communication system. The method includes detecting a prescribed traffic condition in the digital wireless communication system, and outputting a control command based on the detected traffic condition. The control command is output from the digital wireless communication system to at least one selected dual-mode wireless telephone that has registered with the digital wireless communication system. The control command instructs the dual-mode wireless telephone to register with the second wireless communication system. Hence, a dual-mode telephone can be proactively controlled to search for an alternate system based on the digital wireless communication system detecting a prescribed traffic condition.
Use of the control command enables the digital wireless communication system to redirect the selected dual-mode wireless telephone to register with the alternative wireless communication system while in an idle state (i.e., when a call is not is progress). Hence, dual-mode wireless telephones can be easily transferred to alternative wireless communication sy
Cong Le Thanh
D'Agosta Stephen
McDermott & Will & Emery
Verizon Wireless
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