Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1999-03-04
2002-08-20
Bost, Dwayne (Department: 2681)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S343200, C455S414200, C340S007330
Reexamination Certificate
active
06438375
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to wireless communication systems, and more particularly, to a method and apparatus for efficiently communicating different types of control messages between a radio network and a mobile radio station.
BACKGROUND AND SUMMARY OF THE INVENTION
In a typical cellular radio system, a geographical area is divided into cell areas served by base stations which are connected to a radio network. Each user (mobile subscriber) in the cellular radio system is provided with a portable, pocket, hand-held, or car mounted mobile station which communicates voice and/or data with the mobile network. Each base station includes a plurality of channel units including a transmitter, a receiver, and a controller and may be equipped with an omnidirectional antenna for transmitting equally in all directions or with directional antennas, each directional antenna serving a particular sector cell. Each mobile station also includes a transmitter, a receiver, a controller, and a user interface and is identified by a specific mobile station identifier. Each mobile subscriber is identified by another identifier, e.g., an international mobile subscription number (IMSI).
The growth of cellular radio telephone systems has compelled system designers to search for ways to increase capacity. One way to achieve this goal is to increase communications efficiency over the radio interface between the radio network and mobile radio stations. A large portion of the radio bandwidth available at this interface is allocated to carrying substantive traffic between mobile stations and the radio network. However, there is also a considerable amount of control information that must be transmitted between mobile stations and the radio network to perform various operations such as mobile registration, paging, call setup, handover, etc. Some of these operations occur quite frequently. Where possible, it is desirable to reduce the volume and frequency of such signaling to increase the amount of radio bandwidth available for substantive traffic, i.e., increased system capacity.
Besides a limited amount of radio bandwidth, another significant aspect of mobile radio communications is that batteries which power the mobile radio stations have a limited life before recharging is necessary. At least from a user's perspective, the portability of mobile radios is enhanced as the size of those portable radios decreases. But smaller battery size typically results in shorter battery life. Accordingly, a desirable objective is to minimize the drain on a mobile's battery while still providing reasonable access so the mobile radio can be quickly located by the radio network, e.g., in order to set up a call.
In traditional analog cellular systems, when a mobile station is idle, (not using a traffic channel), it tunes to and continuously monitors a control channel corresponding to its current cell in the network. As a result, the mobile can continuously determine whether a page message addressed to it has been received over a control channel. If so, the mobile then transmits a page response over the control channel to the base station which forwards the page response to the radio network. Upon receiving the page response, the radio network selects an available voice channel in the cell from which the page response was received and requests the base station in that cell to order the mobile station via the control channel to establish a through connection. Unfortunately, continuous monitoring of the control channel is a substantial drain on the mobile station battery.
In addition to control messages initiated by the radio network, e.g., pages, a mobile station may access the network to initiate a call by dialing the telephone number and pressing the “SEND” button on the telephone handset. A control signal including the mobile station identifier and the dialed telephone number is transmitted over the control channel to the base station and forwarded to the radio network which validates the mobile station, assigns a traffic channel, and establishes a through connection. If a mobile station moves between cells while a connection is established, a “handover” of that connection takes place between the cells. Handover also requires control signaling over the radio interface.
In addition to call origination and page responses requiring the mobile to access the radio network using control signals, a mobile station often must access the radio network for purposes of location registration. For example, the mobile may periodically register with the radio network so that the network knows the cell, location area, or registration area in which the idle mobile station is currently located. In addition, the idle mobile station also preferably registers with a new cell each time it passes a cell or other area border.
As cellular systems have evolved, plural control channels have been used such as a general system broadcast channel (BCH), a paging channel (PCH), a reverse access channel (RACH) used by mobiles to access the radio network, and forward access channel (FACH) used by the base station to acknowledge mobile accesses over the RACH. In more sophisticated cellular systems, control signaling carried by control channels may be Time-Division Multiplexed (TDM) meaning that one or more mobile stations are assigned or associated with one timeslot in repeated frames of multiple timeslots. One benefit of this TDM approach is that during the other timeslots, an idle mobile station can enter a power savings or sleep mode to extend the life of the mobile's battery. For example, mobile stations may be divided into different paging groups with each paging group being assigned a particular timeslot on a paging control channel. Rather than all mobiles listening to the paging channel for pages all of the time, an idle mobile station need only wake up from sleep mode and monitor the particular timeslot on the paging channel assigned to the paging group to which the mobile station belongs. The mobile station can “sleep” during the other timeslots to save battery power. The amount of time the mobile spends reading paging messages and the time spent asleep represents a tradeoff between call setup delay and power consumption.
An example paging channel format with paging groups is shown in FIG.
1
. The paging channel is divided into plural blocks
1
, . . . , N. corresponding to successive timeslots in a frame. The paging blocks/timeslots are repeated in each successive frame. Paging groups i, i+1, i+2, . . . , i+N−1 may be assigned either statically or dynamically to a corresponding block. Each block corresponding to a paging group includes a page indicator field indicating whether a page currently exists for a mobile in that particular paging group along with a paging message which includes an identification of specific mobile(s) in the group being paged.
Current cellular systems are of the “multiple access” type and therefore must regulate access to limited communication resources by large numbers of mobile stations. As described earlier, mobile stations frequently require access to the radio network in order to register, respond to a page, originate a call, etc. It is therefore desirable to establish access restriction procedures that limit the number of mobiles and/or mobile types which are allowed to perform a particular access procedure, e.g., registration, call origination, etc. Without such restrictions, multiple collisions and large numbers of unsuccessful access attempts may occur. Such collisions, unsuccessful accesses, and successive access re-attempts result in inefficient use of the system and channel resources. Access restrictions may also specify a maximum number of access attempts in a particular time span for a particular mobile access group, a particular minimum mobile priority status or level of service, etc.
One manner for regulating mobile access to the radio communications network is now described in conjunction with an example, uplink random access channel (RACH) illu
Bost Dwayne
Green Miguel D.
Nixon & Vanderhye P.C.
Telefonaktiebolaget LM Ericsson (publ)
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