Multiplex communications – Communication over free space – Combining or distributing information via time channels
Reexamination Certificate
1999-11-05
2004-09-21
Appiah, Charles (Department: 2686)
Multiplex communications
Communication over free space
Combining or distributing information via time channels
C370S321000, C370S328000, C455S424000, C455S458000
Reexamination Certificate
active
06795425
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to wireless communication systems and, more particularly, to methods and apparatus for communicating control information in wireless communications systems.
Cellular radio systems have been operating in the United States since the early 1980s. In a typical cellular radio system as shown in
FIG. 1
, a geographical area (e.g., a metropolitan area) is divided into several smaller, contiguous radio coverage areas (called “cells”) such as cells C
1
-C
10
. The cells C
1
-C
10
are served by a corresponding group of fixed radio stations (called “base stations”) B
1
-B
10
, each of which operates on a subset of the radio frequency (RF) channels assigned to the system. The RF channels allocated to any given cell may be reallocated to a distant cell in accordance with a frequency reuse pattern as is well known in the art. The cellular telephone users (mobile station subscribers) in the cells C
1
-C
10
are provided with portable (hand-held), transportable (hand-carried) or mobile (car-mounted) wireless stations, such as mobile stations M
1
-M
9
, each of which communicates with a nearby base station. The base stations B
1
-B
10
are connected to and controlled by a mobile station services switching center (MSC)
20
. The MSC
20
, in turn, is connected to a central office (not shown in
FIG. 1
) in the landline (wireline) public switched telephone network (PSTN) or to a similar facility such as an integrated system digital network (ISDN). The MSC
20
switches calls between and among wireline and mobile station subscribers, controls signaling to the mobile stations, compiles billing statistics, and provides for the operation, maintenance and testing of the system.
In each cell, at least one RF channel (called the “control” or “paging/access” channel) is used to carry control or supervisory messages, and the other RF channels (e.g., the “voice” or “speech” channels) are used to carry voice conversations. When turned on (powered up), each of the mobile stations M
1
-M
9
enters the idle state (standby mode) and tunes to and continuously monitors the strongest control channel (generally, the control channel of the cell in which the mobile station is located at that moment).
To detect incoming calls, the mobile station continuously monitors the control channel to determine whether a page message addressed to it (ie., containing its MIN) has been received. A page message will be sent to the mobile station, for example, when an ordinary (landline) subscriber calls the mobile station subscriber. The call is directed from the PSTN to the MSC
20
where the dialed number is analyzed. If the dialed number is validated, the MSC
20
requests some or all of the base stations B
1
-B
10
to page the called mobile station throughout their corresponding cells C
1
-C
10
. Each of the base stations B
1
-B
10
which receive the request from the MSC
20
will then transmit over the control channel of the corresponding cell a page message containing the MIN of the called mobile station. Each of the idle mobile stations M
1
-M
9
which is present in that cell will compare the MIN in the page message received over the control channel with the MIN stored in the mobile station. The called mobile station with the matching MIN will automatically transmit a page response over the control channel to the base station which then forwards the page response to the MSC
20
. Upon receiving the page response, the MSC
20
selects an available voice channel in the cell from which the page response was received (the MSC
20
maintains an idle channel list for this purpose), and requests the base station in that cell to order the mobile station via the control channel to tune to the selected voice channel. A through-connection is established once the mobile station has tuned to the selected voice channel.
FIG. 3
shows an exemplary DCCH superframe which includes at least three logical channels, namely, a broadcast control channel (BCCH), a paging channel (PCH), and an access response channel (ARCH). The BCCH, which in this example is allocated 6 DCCH slots, carries overhead messages. The PCH, which is allocated one DCCH slot, carries page messages. The ARCH, which is also allocated one DCCH slot, carries voice or speech channel assignment messages. The exemplary superframe of
FIG. 3
may contain other logical channels, including additional paging channels (if more than one PCH is defined, different groups of mobile stations may be assigned to different PCHs).
A mobile station operating on the DCCH of
FIG. 3
need only be “awake” (monitoring) during certain time slots (e.g., the BCCH and its assigned PCH) in each superframe and can enter “sleep mode” at all other times. While in sleep mode, the mobile station turns off most internal circuitry and saves battery power. Furthermore, by configuring the BCCH as taught in U.S. Pat. No. 5,404,355 to Raith, the mobile station can read (i.e., decode) the overhead messages when locking onto the DCC (e.g., at power-up) and thereafter only when the information has changed, thus resulting in additional battery power savings while allowing for fast cell selection.
Typically only a fraction of the page messages received over the PCH will be directed to the mobile station, as most messages will either be empty messages (“filler” messages containing no page) or pages to other mobile stations. The PCH will usually be operated substantially below the capacity limit in order to avoid excessive traffic blocking (and, hence, delay in delivering pages to the mobile stations). If blocking problems do develop (e.g., because of unanticipated demand) in any cell, the operator can assign additional control channels in that cell or use other capacity-enhancing techniques such as cell splitting. Thus, in general, an appropriately-managed PCH typically will be operated at a level far below maximum capacity, even at busy times. Consequently, more often than not, the PCH carries empty messages. Furthermore, since a mobile station usually receives no more than a few calls each day, most of the non-empty page messages sent on the PCH will be for other mobile stations.
To maximize sleep mode efficiency, the mobile station should be able to detect whether the received page messages are relevant messages (e.g., page messages directed to this particular mobile station) or irrelevant messages (e.g., empty page messages or page messages directed to other mobile stations) as early as possible in the receive processing (e.g., after demodulation but before decoding) so as to avoid as many signal processing steps as possible. Once an irrelevant page is detected, the mobile station can immediately return to sleep. To appreciate the possible power savings from an early detection of irrelevant pages, consider a typical PCH in which a page message is sent once per second. This means that there are (60*60*24=) 86,400 page messages sent to the mobile station each day. If, for example, the PCH carries non-empty page messages only 10% of the time, the mobile station can avoid processing 90% of the page messages if it can detect empty pages. Furthermore, if only a few of the non-empty page messages are directed to this mobile station, it can avoid processing almost all of the page messages transmitted on the PCH if it can also detect that the other non-empty page messages are directed to other mobile stations. Thus, the mobile station effectively can be in sleep mode during PCH reception.
The aforementioned U.S. Pat. No. 5,404,355 describes a technique of grouping information elements and providing an indicator whether the mobile station shall read the associated information elements. This technique is used in current IS-136 to inform the mobile stations about new or changed overhead information. In the PCH channel, change flags are provided to indicate the mobile station to read the overhead information and end-user broadcast messages respectively. Within the broadcast channel (BCCH), change flags are provided for to indicate changes, amendments or deletions
Appiah Charles
Ericsson Inc.
Iqbal Khawar
Myers Bigel & Sibley Sajovec, PA
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