Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
2001-09-07
2004-09-14
Barnie, Rexford (Department: 2682)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S454000
Reexamination Certificate
active
06792268
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention disclosed broadly relates to wireless communications and more particularly relates to RF spectrum monitoring for wireless systems.
2. Related Art
The invention disclosed is related to the copending U.S. patent application Ser. No. 09/401,408, filed Sep. 22, 1999, to Mathilde Benveniste, entitled “Self-Configurable Wireless Systems: Spectrum Monitoring In A Layered Configuration”, assigned to the AT&T Corporation, and incorporated herein by reference.
The invention disclosed is also related to U.S. Pat. No. 5,404,574 to Mathilde Benveniste, issued Apr. 4, 1995, entitled “Apparatus And Method For Non-Regular Channel Assignment In Wireless Communication Systems”, assigned to the AT&T Corporation, and incorporated herein by reference.
The invention disclosed is also related to U.S. Pat. No. 5,809,423 to Mathilde Benveniste, issued Sep. 15, 1998, entitled “Adaptive-Dynamic Channel Assignment Organization System And Method”, assigned to Lucent Technologies, Inc., and incorporated herein by reference.
The invention disclosed is also related to U.S. Pat. No. 5,787,352 to Mathilde Benveniste, issued Jul. 28, 1998, entitled “System and method for management of neighbor-channel interference with power control and directed channel assignment”, assigned to the AT&T Corporation, and incorporated herein by reference.
3. Background
The IS-136 Digital Cellular/PCS Standard
An IS-136 Digital Cellular/PCS system includes one or more cellular radio telephones or mobile devices within the communications range of a base station. The base station can have one or more radio transceivers, a control computer, and an antenna system. The base station is connected by means of a mobile switching center (MSC) to the public switched telephone network (PSTN). The mobile switching center provides the functionality of a telephone central office and is additionally responsible for call processing, mobility management, and radio resource management. The IS-136 Digital Cellular/PCS network architecture and system operation are specified by the
Telecommunications Industry Association, TIA/EIA Interim Standard: TDMA Cellular/PCS
-
Radio Interface—Mobile Station
-
Base Station Compatibility, Revision A, TIA/EIA/IS
-136-
A
, October 1996.
FIG. 1
shows the prior art state diagram of an IS-136 compliant mobile device. A mobile's operation is carried out in processes that occur when it transitions from one state to another. The processes are carried out by software in the mobile. State
102
is the null state when the mobile is powered down. Upon being powered up by the power up action path
120
, the mobile transitions to state
104
which is the Control Channel Scanning and Locking state. A mobile executes the DCCH Scanning and Locking procedure while in this state, attempting to find a digital control channel (DCCH). A mobile executes the Control Channel Selection procedure from the Control Channel Scanning and Locking state
104
once a DCCH is found using the DCCH Scanning and Locking procedure. The Control Channel Selection procedure is executed in order to determine if the DCCH is suitable for camping.
Communication between the mobile device and the base station employs a time division multiple access (TDMA) frame structure shown in
FIG. 2
, where each frame
200
and
200
′ has six time slots. Frames
200
and
200
′ shown in
FIG. 1
, occur at different frame times in the same 30-kHz RF channel. In the digital PCS full rate mode, each user is allowed access to two of the six time slots in a frame, so one RF channel can simultaneously serve up to three users. The frames have a duration of 40 ms and are organized into superframes of 16 TDMA frames, having a duration of 640 ms. A hyperframe consists of two superframes, and has a duration of 1.28 seconds. Frequency division multiple access (FDMA) is used to support more users by assigning multiple RF channels for use in the same cell. A mobile user transmits in the reverse or uplink direction on one frequency and receives in the forward or downlink direction on a different frequency, using frequency division duplexing (FDD).
Only one forward digital control channel (DCCH) consisting of two time slots
202
and
208
in one RF channel of
FIG. 2
, is required in the forward or downlink direction from the base station to the mobiles. Similarly, only one reverse digital control channel (DCCH) consisting of two time slots in another RF channel, is required in the reverse or uplink direction from the mobiles to the base station. The logical channels of the DCCH in the forward direction (from the base station to the mobile) are divided into broadcast channels and point-to-point channels, while the reverse DCCH is a point-to-point channel. The frame
200
shown in
FIG. 2
carries the forward digital control channel (DCCH) containing control channel selection parameters for SCANINTERVAL in time slot
202
and DELAY VALUE in time slot
208
. Time slots
204
and
210
carry traffic from the base station (BS) to mobile
20
and time slots
206
and
212
carry traffic from the base station (BS) to mobile
20
′. The frame
200
A shown in
FIG. 2
carries the forward digital control channel (DCCH) containing the access parameter for MAX_RETRIES in time slot
214
. Time slots
216
and
222
carry traffic from the base station (BS) to mobile
20
and time slots
218
and
224
carry traffic from the base station (BS) to mobile
20
′. Time slot
220
carries other forward digital control channel (DCCH) broadcast channel messages or point-to-point control channel messages.
Once a suitable digital control channel (DCCH) is found, action path
121
causes the mobile to transition to the DCCH Camping state
106
in FIG.
1
. The DCCH Camping state
106
is the normal state for the mobile while in service on a DCCH and not processing a call. Upon entering the DCCH Camping state, a mobile must read control information from the base station contained in the DCCH messages
140
. This information includes control channel selection parameters used by the mobile in the reselection of a DCCH, including the SCANINTERVAL parameter and the DELAY parameter. This information also includes access parameters used by the mobile to access the base station, including the MAX_RETRIES parameter. The mobile periodically executes a number of processes and procedures while in the DCCH Camping state
106
, including control channel reselection. A mobile remains in the DCCH Camping state
106
while it reselects from one DCCH to another. In the process reselection to select the best DCCH, the mobile periodically measures the received signal strength on the neighboring control channels from base stations in neighboring cells. The mobile then evaluates whether another base station's control channel would be better. If a better control channel is found, the mobile tunes to the new base station's control channel, synchronizes, and begins to monitor it for messages.
While in the DCCH Camping state
106
, a mobile periodically measures the signal strength on the current DCCH and all control channels in the neighbor cell list. This measurement process is called the Control Channel Locking procedure, and is executed every SCANINTERVAL. The Control Channel Locking procedure is part of the Control Channel Reselection procedure. The mobile must wait for a delay interval timed by its camping state delay timer
106
A, whose maximum delay value is set by the DELAY parameter, before the mobile can begin periodically measuring the signal strength. The DELAY parameter keeps the mobile from considering a neighboring control channel as a reselection candidate until the time delay has been met.
Once the DELAY interval has expired in camping state delay timer
106
A, the mobile executes the Control Channel Reselection procedure to find a better control channel from which to obtain service. It typically invokes this procedure from the DCCH Camping state
106
over action path
132
. In the Control Channel Locking proced
Benveniste Mathilde
Prabhu Sushil Kumar
AT&T Corporation
Barnie Rexford
Morgan & Finnegan , LLP
Redmond, Jr. Joseph C.
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