Method and system for overhead message updates

Details Method and system for overhead message updates Method and system for overhead message updates

1998-09-30

2002-04-16

Hunter, Daniel (Department: 2684)

Telecommunications

Radiotelephone system

Zoned or cellular telephone system

C455S434000, C455S445000, C455S455000, C455S458000, C455S464000, C455S550100

Reexamination Certificate

active

06374103

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to the field of wireless communications and more particularly to the field of overhead messaging in code division multiple access systems.
BACKGROUND OF THE INVENTION
A code division multiple access (CDMA) cellular telephone system uses spread spectrum technology to allow multiple users access to the same frequency band. The Telecommunication Industry Association and the Electronics Industry Association have adopted a standard, TIA/EIA IS-95 (IS-95), for digital cellular phone applications using CDMA techniques. Such IS-95 systems are disclosed in detail in Garg, Smolik and Wilkes, Applications of CDMA In Wireless/Personal Communications, Prentice Hall, 1997.
A CDMA system uses pseudorandom noise (PN) sequences to spread base station and mobile signals to the transmission bandwidth. Transmitted signals using different PN sequences can be received at the receiver, and the PN sequences allow the receiver to distinguish a desired signal from all the received signals.
The geographic coverage provided by a CDMA cellular telephone system is divided into coverage cells, where each cell corresponds to a base station. The cell may be further divided for certain types of base stations into multiple sectors, where each sector uses multiple carrier channels.
In an IS-95 system, the parameters a mobile uses to establish and maintain a call are transmitted as a set of over the air (OTA) messages, known as overhead messages, by every base station in the network. In a mobile originated call, the mobile determines if it has a current set of overhead messages before requesting traffic channel resources.
If the overhead messages are not up to date, the mobile monitors the paging channel to update the overhead messages. Once the mobile updates its overhead messages, it begins the access procedure. The likelihood of success of an origination attempt is related to the time taken to complete overhead message updates. The longer the process takes, the more likely the mobile is to leave the cell's coverage area, causing an access failure.
SUMMARY OF THE INVENTION
This invention provides a method for reducing the time for a mobile to update overhead messages prior to making an access attempt, thereby improving the call origination success rate. The method takes advantage of time slots on the paging channel which are typically filled with a null message. According to this invention, a base station transmits a selected overhead message, in lieu of a null message. Because overhead messages are thereby transmitted more frequently, the mobile cycles through required messages and updates its parameters in a reduced time.
In one embodiment, the base station runs a timer to determine the paging channel slots that must contain an overhead message. In the intervening slots or slot fragments, the base station transmits mobile-directed messages, when they are available. When no mobile directed messages are available for transmission and the timer has not signaled that an overhead message must be sent, the base station selects an overhead message from a queue for transmission on the paging channel slot or slot fragment.
The actual selection algorithm for the overhead message is not critical, although the various overhead messages should be selected with approximately the same frequency. A base station operating according to the method of the invention sends overhead message updates more frequently without consuming additional paging channel capacity, since the existing paging channel resources are used more efficiently.


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Varma, V K et al., “Integrated Alerting and System Broadcast Channel for a Wireless Access System,” Feb. 1, 1996, vol. 45.

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