Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1999-04-08
2001-01-30
Maung, Nay (Department: 2744)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S422100, C455S432300, C455S439000, C455S517000
Reexamination Certificate
active
06181942
ABSTRACT:
BACKGROUND OF THE INVENTION
I. Field of the Invention
The present invention relates to spread spectrum telecommunications systems. More particularly, the present invention relates to a novel and improved messaging method and apparatus in a CDMA cellular communication system.
II. Description of the Related Art
The use of code division multiple access (CDMA) modulation techniques is one of several techniques for facilitating communications in which a large number of system users are present. Although other techniques such as time division multiple access (TDMA), frequency division multiple access (FDMA), and amplitude modulation (AM) schemes such as amplitude companded single sideband (ACSSB) are known, CDMA has significant advantages over these other techniques. The use of CDMA techniques in a multiple access communication system is disclosed in U.S. Pat. No. 4,901,307, entitled “SPREAD SPECTRUM MULTIPLE ACCESS COMMUNICATION SYSTEM USING SATELLITE OR TERRESTRIAL REPEATERS,” assigned to the assignee of the present invention and incorporated by reference herein.
In the CDMA cellular system, a large number of mobile telephone system users, each having a transceiver, communicates through satellite repeaters or terrestrial stations which are also referred to as cells. Each cell includes a physical plant called a base station. A cell covers a limited geographic area and routes calls carried over cellular telephones to and from a telecommunication network via a mobile switching center. When a cellular telephone user moves into the geographic area of a new cell, the routing of that user's call may be eventually made through the new cell by a process called a “handoff.”
A cellular telephone or, more specifically, a mobile station, broadcasts a signal that is received by a base station. The signal is then relayed to a mobile switching center which in turn routes the signal to the public switched telephone network and to telephone lines or other mobile stations. Similarly, a signal may be transmitted from the public switched telephone network to a mobile station via a base station and a mobile switching center. The communications channel allocated for communication of information between the mobile station and the base station is called the traffic channel.
The interface between the mobile station and the base station is referred to as the Air-Interface. The telecommunications industry association (TIA) has provided a standard for CDMA call processing on the Air-Interface entitled “IS-95-A Mobile Station—Base Station Compatibility Standard for Dual Mode Wideband Spread Spectrum Cellular System,” hereinafter IS-95-A, which is incorporated by reference. The interface between the base station and the mobile switching center is referred to as the A-Interface. The TIA has provided for call processing on the A-Interface through the standard provided in “IS-634 Mobile Switching Center—Base Station Interface for Public 800 MHz,” which is also incorporated by reference. IS-95-A and IS-634 both define the messages and signals that are sent on their respective interfaces for the operation of a CDMA cellular telephone call.
The call flow in a CDMA environment requires processing on both the Air-Interface and the A-Interface. The successful progression of a call requires that the proper messages and signals are sent at the right times on both the Air-Interface and the A-Interface. The IS-634 standard is being developed to provide for call processing on the A-Interface. A number of problems and deficiencies are present in IS-634 which currently does not support some of the necessary operations on the A-Interface. Some of these problems and deficiencies are recognized and solved by the present invention in the manner described below.
SUMMARY OF THE INVENTION
The present invention is a novel and improved method and apparatus for providing a new message on the interface between a mobile switching center and a base station, also known as the A-Interface, of a cellular telephone system. The present invention recognizes that the A-Interface, as presently defined by the IS-634 standard, does not support some of the operations necessary for reliable call processing. Introduction of the new message will provide support for required functionality on the A-Interface.
The present invention recognizes that improvements are needed for the A-Interface to reliably handle the call waiting and the hard handoff procedures. An Alert With Information Message is introduced on the A-Interface to improve the operation of these procedures.
Using the call waiting feature, a mobile station may have a first party of a public switched telephone network put on hold while being connected to a second party. If the second party hangs up, then according to the current procedure, a Release/Clear Message (or an equivalent message) is sent to the mobile station, causing the mobile station to release its traffic channel. A new traffic channel must then be reestablished to reconnect the mobile with the first party. The present invention recognizes that the current procedure is unreliable in that difficulties may arise in the process of reconnecting the mobile with the first party. Moreover, Air-Interface resources are used inefficiently as the current procedure requires the release of the traffic channel and the reassignment of a new channel. To overcome these shortcomings, an Alert With Information Message is sent on the A-Interface to the base station, triggering the transmittal of an Alert With Information Message on the Air-Interface. Upon receipt of the Alert With Information Message, the mobile station is prompted to transmit a Connect Message to the mobile switching center via a base station. The mobile switching center then reconnects the first party to the mobile station, without the need to reestablish a new traffic channel.
A hard handoff occurs in a cellular system when a mobile station moves from the coverage area of one base station to the coverage area of another base station. During a mobile station terminated call, in order for the mobile to undertake handoff, it must first receive an Alert With Information Message transmitted by the base station. Under current procedure, the Alert With Information Message is generated and transmitted solely by the base station in whose coverage area the mobile is currently located. The present invention recognizes that the current procedure may cause the hard handoff procedure to be unreliable. If the mobile moves from the coverage area of a first base station to the coverage area of a second base station, the mobile station may never receive the Alert With Information Message from the first base station, resulting in a dropped call. Thus, the present invention provides for an Alert With Information Message to be generated and transmitted by the mobile switching center. While the mobile station is moving from the coverage area of the first base station to that of the second base station, the mobile switching center transmits the Alert With Information Message to the second base station. The second base station in turn transmits an Alert With Information Message to the mobile station. Having received the Alert With Information Message, handoff can now proceed without the call being dropped.
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Baker Kent D
Beladi S. Hossain
Maung Nay
Qualcomm Incorporated
Wadsworth Philip R
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