Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
2000-06-12
2002-11-05
Urban, Edward F. (Department: 2685)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S515000, C455S574000, C370S311000, C370S313000, C370S314000
Reexamination Certificate
active
06477382
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The field of the present invention relates to wireless communication and, more particularly, to paging techniques in a wireless communication system.
2. Description of Related Art
A mobile communication system may generally comprise a set of “user stations,” typically mobile and the endpoints of a communication path, and a set of “base stations,” typically stationary and the intermediaries by which a communication path to a user station may be established or maintained. A group of base stations may be connected to a base station controller, or a cluster controller, which can in turn be connected to a local public telephone network through, for example, a mobile switching center.
It is generally desirable in a mobile communication system to achieve the greatest possible user traffic capacity at a base station, so that fewer base stations need to be deployed in order to serve user demands. A variety of techniques have been developed or proposed by which a base station is able to communicate with multiple user stations. Such techniques generally each include some means for distinguishing transmissions between different cells and/or between different user stations within a cell. For example, a communication system in which transmissions are distinguished according to the transmission frequency may be referred to as a frequency division multiple access (FDMA) communication system. A communication system in which a forward link transmission over one frequency is paired with a reverse link transmission over a different frequency may be referred to as a frequency division duplex (FDD) communication system. A communication system in which transmissions are distinguished according to the relative timing of the transmission (i.e., by use of time slots) may be referred to as a time division multiple access (TDMA) communication system. A communication system in which a forward link transmission during one time slot (or time segment) is paired with a reverse link transmission occurring during a different time slot (or time segment) may be referred to as a time division duplex (TDD) communication system. A communication system in which transmissions are distinguished according to which code is used to encode the transmission may be referred to as a code division multiple access (CDMA) communication system.
In a CDMA communication system, the data to be transmitted is generally encoded in some fashion, in a manner which causes the signal to be “spread” over a broader frequency range and also typically causes the signal power to decrease as the frequency bandwidth is spread. At the receiver, the signal is decoded, which causes it to be “despread” and allows the original data to be recovered. Distinct codes can be used to distinguish transmissions, thereby allowing multiple simultaneous communication, albeit over a broader frequency band and generally at a lower power level than “narrowband” systems. Different users may thereby transmit simultaneously over the same frequency without necessarily interfering with one another.
In addition to the above, various “hybrid” communication systems incorporating aspects of more than one multiple access communication technique have been developed or proposed.
Initial communication between a user station and a base station can be established either when the user station seeks to initiate communication with a base station (for example, attempting to initiate a telephone call), or when the base station attempts to complete a call to the user station (for example, where the user station is paged). In many conventional mobile communication systems, a dedicated control channel is used to assist mobile stations in establishing communication. According to this technique, the mobile station first communicates over the control channel when establishing communication. The base station then assigns to the mobile station a “permanent” communication channel for exchanging bearer traffic messages for the duration of the call. Particular techniques for establishing initial communication between a base station and a user station are described, for example, in U.S. Pat. No. 5,455,822, U.S. Pat. No. 5,737,324, U.S. Pat. No. 5,671,219, U.S. Pat. No. 5,648,955, and U.S. Pat. No. 5,787,076, each of which is assigned to the assignee of the present invention, and each of which is hereby incorporated by reference as if set forth fully herein.
When a base station pages a user station, the base station typically sends a paging message directed to the specific user station (e.g., by including a specific user station identifier, which may be obtained from the user station at initial registration). Often a special broadcast channel is reserved for this paging purpose, sometimes in conjunction with additional broadcast functions. When the user station receives a paging message, it responds according to the particular communication protocol employed by the system, and thereby receives the incoming call. If more than one paging request is received at the base station, the base station may transmit multiple paging messages sequentially over the broadcast channel. The base station may repeat a paging message, or a group of paging messages, until each user station responds or a paging timeout occurs.
It has been found convenient in many mobile communication systems to allow user stations (particularly cellular telephone handsets) to remain in a low-power, dormant state (i.e., a sleep state) while no call is in progress, becoming active periodically (i.e., awakening) only long enough to determine whether it is being paged. In a typical mobile communication system, a handset awakens or otherwise activates at regular, fixed intervals to monitor the broadcast paging channel from the base station. If the handset receives a paging message during the time it is awake or active, it does not return to sleep or dormancy, but instead responds to the paging message according to the system protocol in an attempt to receive the incoming call. On the other hand, if no paging message for the handset is received, the handset returns to a sleep or dormant state.
In most mobile communication systems, paging is only one of a number of broadcast functions carried out by the base station. Where multiple broadcast functions are performed by the base station, the base station broadcast channel may be shared between paging functions other broadcast functions by, for example, time multiplexing paging messages and other messages. A result is that paging messages may only be sent periodically by the base station. However, if the handset wakes up and monitors the broadcast channel at the wrong times (i.e., at times other than when paging messages are being broadcast from the base station), the handset will miss any paging messages directed to it. One solution to this problem is to define a preset time slot or time interval for broadcasting paging information from the base station. Once the handset locks on to the paging channel, it wakes up at regular intervals matched to the transmission repetition rate of the paging channel. The handset thereby has an increased likelihood of receiving a page, since it will monitor the paging channel only at times when paging information is being transmitted. As a benefit of such an approach, the time which a handset can spend asleep or dormant is increased (thus saving power and increasing battery life), because there is a general assurance that the handset will not miss a page when the handset is asleep or dormant, particularly if the page is repeated a reasonable number of times.
While the above solution may increase power savings at the handset, it is not a totally adequate solution. It suffers from the drawback that the same amount of base station resources are consumed with paging traffic no matter whether the paging traffic is heavy or light. Reserving resources for paging traffic prevents the use of such resources for other broadcast needs. If too many resources are reserved for paging at a given time, the system is ineffic
Bilgic Izzet M.
Gavette Sherman L.
Gibbs Benjamin K.
Mansfield Carl
Blakely , Sokoloff, Taylor & Zafman LLP
Davis Temica M.
Urban Edward F.
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