Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1999-07-08
2002-04-02
Maung, Nay (Department: 2681)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S436000
Reexamination Certificate
active
06366781
ABSTRACT:
BACKGROUND OF THE PRESENT INVENTION
1. Field of the Invention
The present invention relates generally to telecommunications systems and methods for positioning a mobile station within a cellular network, and specifically to positioning a mobile station during a handover.
2. Background of the Present Invention
Cellular telecommunications is one of the fastest growing and most demanding telecommunications applications. Today it represents a large and continuously increasing percentage of all new telephone subscriptions around the world. A standardization group, European Telecommunications Standards Institute (ETSI), was established in 1982 to formulate the specifications for the Global System for Mobile Communication (GSM) digital mobile cellular radio system.
With reference now to
FIG. 1
of the drawings, there is illustrated a GSM Public Land Mobile Network (PLMN), such as cellular network
10
, which in turn is composed of a plurality of areas
12
, each with a Mobile Switching Center (MSC)
14
and an integrated Visitor Location Register (VLR)
16
therein. The MSC
14
provides a circuit switched connection of speech and signaling information between a Mobile Station (MS)
20
and the PLMN
10
. The MSC/VLR areas
12
, in turn, include a plurality of Location Areas (LA)
18
, which are defined as that part of a given MSC/VLR area
12
in which the MS
20
may move freely without having to send update location information to the MSC
14
that controls the LA
18
. Each LA
18
is divided into a number of cells
22
. The MS
20
is the physical equipment, e.g., a car phone or other portable phone, used by mobile subscribers to communicate with the cellular network
10
, each other, and users outside the subscribed network, both wireline and wireless.
The MSC
14
is in communication with at least one Base Station Controller (BSC)
23
, which, in turn, is in contact with at least one Base Transceiver Station (BTS)
24
. The BTS is the physical equipment, illustrated for simplicity as a radio tower, that provides radio coverage to the cell
22
for which it is responsible. It should be understood that the BSC
23
may be connected to several BTS's
24
, and may be implemented as a stand-alone node or integrated with the MSC
14
. In either event, the BSC
23
and BTS
24
components, as a whole, are generally referred to as a Base Station System (BSS)
25
.
The MS
20
and the BTS
24
communicate over a radio interface, which utilizes the Time Division Multiple Access (TDMA) concept, with one TDMA frame per carrier frequency. The TDMA frames are numbered in a cyclic pattern. Each TDMA frame consists of a number of time slots, in which each time slot is referred to as a physical channel. Depending upon the type of information being transmitted, different types of logical channels are mapped onto these physical channels. For example, to transmit speech, the logical channel “traffic channel” must be mapped onto one of the physical channels. The information sent on one of these channels is called a burst.
With further reference to
FIG. 1
, the PLMN Service Area or cellular network
10
includes a Home Location Register (HLR)
26
, which is a database maintaining all subscriber information, e.g., user profiles, current location information, International Mobile Subscriber Identity (IMSI) numbers, and other administrative information, for subscribers registered within that PLMN
10
. The HLR
26
may be co-located with a given MSC
14
, integrated with the MSC
14
, or alternatively can service multiple MSCs
14
, the latter of which is illustrated in FIG.
1
.
Determining the geographical position of an MS
20
within a cellular network
10
has recently become important for a wide range of applications. For example, location services (LCS) may be used by transport and taxi companies to determine the location of their vehicles. In addition, for emergency calls, e.g., 911 calls, the exact location of the MS
20
may be extremely important to the outcome of the emergency situation. Furthermore, LCS can be used to determine the location of a stolen car, for the detection of home zone calls, which are charged at a lower rate, for the detection of hot spots for micro cells, or for the subscriber to determine, for example, the nearest gas station, restaurant, or hospital, e.g., “Where am I” service.
As can be seen in
FIG. 2A
, which will be described in connection with the signaling diagram in
FIG. 2B
of the drawings, upon the reception of a positioning request from a Location Services (LCS) client (step
200
), the MSC
14
sends a MAP_PERFORM_LOCATION message to a Serving Mobile Location Center (SMLC)
270
within the PLMN
10
associated with the MSC
14
(step
205
). The SMLC
270
is responsible for carrying out the positioning request and calculating the MS
20
location. It should be noted that more than one SMLC
270
may be located within each PLMN
10
. Thereafter, the SMLC
270
determines the positioning method to use (step
210
), and if the Time of Arrival (TOA) positioning method is selected, the SMLC
270
returns a MAP CHANNEL INFORMATION message to the MSC
14
(step
215
). The MSC
14
, in turn, forwards a BSSMAP CHANNEL INFORMATION message to the serving BSC
23
, requesting the physical channel description of the traffic channel that will be used to perform a positioning handover (step
220
). The message also includes information on the cell
22
ID's and TDMA frame numbers for the serving and candidate cells
22
to which positioning handovers are to be performed to, along with a value for a delta timer
27
.
In response, the BSC
23
sends a BSSMAP CHANNEL INFORMATION ACK message to the MSC
14
, which includes the requested physical channel description (step
225
). In addition, the BSC
23
starts the delta timer
27
(step
230
). The MSC
14
forwards this physical channel description received from the BSC
23
to the SMLC
270
(step
235
), which uses this physical channel description to configure at least three Location Measurement Units (LMUs)
260
(only one of which is shown) within the PLMN
10
. The LMUs
260
are responsible for obtaining positioning measurements and providing these measurements to the SMLC
270
for use in calculating the location of the MS
20
. All communication to and from the LMUs
260
are sent over the air interface. Therefore, each LMU
260
is in wireless communication with an associated BTS
24
. The SMLC
270
selects which LMUs
260
should obtain the positioning measurements (step
240
), and sends LCS Information Request messages to each of these selected LMUs
260
(step
245
).
At the expiration of the delta timer
27
within the BSC
23
(step
250
), the BSC
23
begins the positioning handover process. The delta timer
27
is used to ensure that the SMLC
270
has enough time to configure the LMUs
260
prior to initiating the positioning handover process. A positioning handover occurs when the BSC
23
sends a HANDOVER (HO) COMMAND message to the MS
20
(step
255
), instructing the MS
20
to perform a handover to the serving BTS
24
or a target BTS (not shown) on a specified channel. The HO COMMAND message also indicates the TDMA frame number that the MS
20
should begin sending access bursts. When the MS
20
starts sending the access bursts in a HANDOVER ACCESS message (step
260
), the configured LMUs
260
measure the Time of Arrival (TA) of these access bursts (step
265
). Since the handover is a positioning handover, and not a radio-related handover, the BTS
24
will not respond to the HANDOVER ACCESS message, and the MS
20
will stop sending the access bursts upon the expiration of a timer (not shown) within the MS
20
. Thereafter, the MS
20
returns to the old channel that it was assigned to, and sends a HANDOVER FAILURE message to the BSC
23
(step
270
).
These TOA measurements are forwarded from the LMUs
260
to the SMLC
270
(step
275
) for use in assisting the calculation of the geographical location of the MS
20
(step
280
). After the SMLC
270
calculates the MS
20
Hussain Tahir
Zadeh Bagher
Ericsson Inc.
Maung Nay
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