Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1999-07-28
2002-05-07
Trost, William (Department: 2683)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S436000, C455S456500, C370S331000, C342S357490
Reexamination Certificate
active
06385452
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 using a time of arrival (TOA)-based positioning method.
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. Each TDMA frame consists of a number of time slots, with one time slot per carrier frequency. 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. In addition, the TDMA frames are numbered in a cyclic pattern.
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. 2
of the drawings, upon the reception of a positioning request from a Location Services (LCS) client
280
, the MSC
14
sends a Mobile Application Part (MAP) PERFORM LOCATION message to a Serving Mobile Location Center (SMLC)
270
within the PLMN
10
associated with the MSC
14
. 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. If the Time of Arrival (TOA) positioning method is selected, the SMLC
270
returns a MAP CHANNEL INFORMATION message to the MSC
14
. The MSC
14
, in turn, forwards a Base Station Subsystem MAP (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. 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.
In response, the BSC
23
sends a BSSMAP CHANNEL INFORMATION ACK message to the MSC
14
, which includes the requested physical channel description. The MSC
14
forwards this physical channel description to the SMLC
270
, which uses the 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, unless the LMU
260
is integrated with a BTS
24
, each LMU
260
is in wireless communication with at least one associated BTS
24
.
Once the SMLC
270
selects which LMUs
260
should obtain the positioning measurements, the SMLC
270
sends LCS Information Request messages to each of these selected LMUs
260
. The LCS Information Request messages specify the absolute time that the LMUs
260
should begin to measure the time of arrival (TOA) of access bursts transmitted by the MS
20
. The LMUs
260
only have knowledge of the absolute time, and do not have any information on the current TDMA frame number. Therefore, this absolute time must correspond to the TDMA frame number transmitted by the SMLC
270
to the BSC
23
in the CHANNEL INFORMATION message in order for positioning to occur. For example, if the transmitted TDMA frame number corresponds to starting time t
0
for one of the LMUs
260
, but the SMLC
270
instructs that LMU
260
to begin listening at starting time t
1
, then that LMU
260
will not begin listening to the access bursts transmitted by the MS
20
at the correct time. Thus, that LMU
260
will not be able to obtain positioning measurements, and, as a consequence, the SMLC
270
will not be able to calculate the location of the MS
20
.
Therefore, TOA-based positioning requires knowledge of the relation between the absolute time and air interface timing, e.g., the TDMA frame number. Currently, the LMUs
260
monitor the TDMA frame number on a synchronization channel of an associated BTS
24
and determine the corresponding absolute time using a GPS receiver within the LMU
260
for that TDMA frame number. Thereafter, the LMU
260
periodically sends this information to the SMLC
270
, which, in turn, stores this relation information in a database
275
therein. Later, when a positioning request is received, the SMLC
270
uses this relation information in the LMU
260
Lindqvist Dan
Zadeh Bagher R.
Ericsson Inc.
Jenkens & Gilchrist P.C.
Nguyen Simon
Trost William
LandOfFree
System and method for determining absolute time based upon... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with System and method for determining absolute time based upon..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and System and method for determining absolute time based upon... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2830621