WO2001019122A1

WO2001019122A1 - Method and network for providing to a positioning data

Info

Publication number: WO2001019122A1
Application number: PCT/US2000/024202
Authority: WO
Inventors: Bikash Saha; Shahrokh Amirjoo
Original assignee: Ericsson Inc.
Priority date: 1999-09-03
Filing date: 2000-08-31
Publication date: 2001-03-15
Also published as: BR0013736A; CN1382361A; EP1212917A1; AU7345900A; KR20020057954A

Abstract

In a wireless communications network (10), a method of providing Time of Arrival (TOA) positioning data that minimizes the use of traffic channels within the network. The method comprising the steps of assigning a signaling channel (62) to an idle mobile station (12) within the network (10), causing a handover (68) of the mobile station (12) directly from the signaling channel (62) to a traffic channel (66), causing the mobile station (12) to generate an access burst during handover (68), and utilizing the access burst to provide TOA positioning data for the mobile station (12).

Description

METHOD AND NETWORK FOR PROVIDING TO A POSITIONING DATA

TECHNICAL FIELD

This invention relates generally to cellular communications and applications, and more particularly to a method of providing Time Of Arrival (TOA) positioning data that minimizes the use of traffic channels within the wireless network.

BACKGROUND OF THE INVENTION

The increased demand for wireless (or cellular) communications has resulted in advanced communications systems capable of providing a high quality of service to an increasing number of users. The systems that have emerged include analog systems such as the Advanced Mobile Phone System (AMPS), and digital systems such as the Global System for Mobile Communications (GSM) and Digital AMPS (D-AMPS). To implement these systems, cellular based communication devices operate in interference- limited environments that rely on frequency reuse plans to maximize capacity and quality. Protocols such as the Frequency Division Multiple Access (FDMA) in analog systems, and the Time Division Multiple Access (TDMA) in digital systems are used for this purpose.

Because bandwidth is a limited resource (both in a physical and regulatory sense), schemes to divide the available network resources among as many subscribers as possible are often employed. One such scheme which seeks to maximize bandwidth allocation efficiency involves a combination TDMA and FDMA (TDMA FDMA). For example, a 25 MHZ bandwidth can be divided into 124 carrier frequencies spaced 200 kHz apart, with one or more carrier frequencies assigned to each Base Station in the network. Each of the carrier frequencies, in turn, can be divided in time using a TDMA scheme to define logical channels. Channels, in turn, may be divided into dedicated subchannels which are allocated to a mobile station.

A traffic channel, also commonly called a communication or transmission channel, is used to carry speech and data (typically non- command) signals over the network. Traffic channels are defined in GSM using a multi-frame, or a group of 26 separate TDMA frames. With 26 frames, typically 24 will be used for speech or data, one as a control channel, and one will be unused.

Control channels, also commonly called signaling or common channels, can be accessed both by idle mode and dedicated mode mobiles. The common channels are used by idle mode mobile to exchange the signaling information required to change to dedicated mode. Mobile systems in the dedicated mode monitor the radio transmissions from the serving base transceiver station for handover and other information. The common channels are defined within a 51 -frame multi-frame, so that dedicated mobile stations using the 26-frame multi-frame Traffic Channel (TCH) structure can still monitor control channels.

In other systems, such as Code Division Multiple Access (CDMA) or FDMA, other methods are used. In addition to dividing bandwidth among subscribers, traffic channels are assigned or allocated to incoming calls. Different approaches and protocols may be employed to increase channel efficiency, connection quality, and the number of potential channels available for subscribers within a base station operating area. Transmissions channel in the system facilitate communications in the system. As the use of the wireless network increases, so does the importance of determining the location or "positioning" of users within the network. Positioning algorithms and systems are being developed and used to calculate and render positioning coordinates of a user. At the same time, positioning has become mandated by government agencies (i.e., FCC) as a standard to be implemented as early as the year 2001. The Time of Arrival (TOA) positioning mechanism is based on collecting time of arrival (TOA) measurements computed from access bursts generated by the mobile station. Access bursts are generated during either inter-cell or intra-cell handover and are received and measured by both serving and neighboring base transceiver stations (BTSs). Utilizing access bursts to position the mobile requires additional hardware at the listening BTSs to accurately measure the TOA of the bursts.

In the current TOA positioning method, a Mobile Station (MS), also referred to as a mobile radio, mobile, or mobile handset, which is in idle mode is first assigned a signaling channel before paging, authentication and ciphering is completed. At such point, the Serving Mobile Location Center (SMLC) then instructs the Base Station Controller (BSC) through the Mobile Switching Center (MSC) to assign a first traffic channel. This process if often referred to as positioning call set-up. The SMLC then directs the BSC to perform a positioning handover (i.e., fake handover) to another traffic channel in order to send a handover access burst from the MS to an array of Location Management Units (LMUs) which obtain the TOA positioning of the MS.

This use of transmission channels for positioning in this manner is inefficient and wastes valuable network resources. The use of traffic channels for positioning a mobile station in the idle mode results in greater load on the network. As such, a means of reducing the use of traffic channels during positioning would provide numerous advantages.

SUMMARY OF THE INVENTION

The present invention provides a method in a wireless communications network of providing Time of Arrival (TOA) positioning data that minimizes the use of traffic channels within the network. The present invention is providing a new solution for TOA positioning where the idle MS is first assigned a signaling channel and then directly handed over to a traffic channel. The Serving Mobile Location Center (SMLC) instructs the Base Station Controller (BSC) via the Mobile Serving Center (MSC) to perform positioning handover (i.e., fake handover) directly from the signaling channel to a traffic channel reserved for that purpose. Decreased load on the network without tying up unnecessary network resources is one advantage provided by the present invention.

Disclosed in one embodiment is a method of providing Time of Arrival (TOA) positioning data that minimizes the use of traffic channels within a wireless communications network. The method comprises the steps of assigning a signaling channel to an idle MS within the network and causing a handover of the mobile station directly from the signaling channel to a traffic channel. A SMLC in communication with the BSC instructs the BSC to perform a handover. That is, the SMLC transmits a positioning handover instruction to the BSC via the MSC. The BSC serving the MS then performs a handover from the signaling channel to the traffic channel.

The method can further comprise the steps of causing the MS to generate an access burst during handover. The step is performed by sending a handover access burst from the MS to a set of Location Management Units (LMUs) used in one embodiment, the access burst is utilized to provide TOA positioning data for the MS.

Also disclosed is a method of providing Time of Arrival (TOA) positioning data for a MS, the wireless communications network having a Serving Mobile Location Center (SMLC) communicably coupled and adapted to instruct a Base Station Controller (BSC) serving the MS via a Mobile Station Controller (MSC). The method comprises the step of causing a Location Services (LCS) Information Request (TOA) to be transmitted from the SMLC to the MSC. Next, a Location Information Command (TOA) is generated and transmitted from the MSC to the BSC. This step can be performed by reporting Location Information (TOA) to the MSC. The reporting step is then followed by the step of sending a LCS Information Report (TOA) from the MSC to the SMLC.

The method can further comprise the step of causing a LCS Information Request to be transmitted from the MSC to a plurality of Location Management Units (LMUs) adapted to measure TOA access bursts generated by the MS. The LMUs are then adapted to relay a LCS Information Response to the MSC. Once the response has been transmitted, the SMLC then performs a location acknowledgment which is then sent to the MSC. The method can also comprise the steps of assigning a Stand Alone

Dedicated Control Channel (SDCCH) to the MS, transmitting a handover command to the MS, and performing a handover of the MS from the SDCCH to a traffic channel and causing the MS to generate an access burst during the handover step so that the plurality of LMUs can measure the TOA of the access burst for positioning of the MS. Such steps are accompanied by the step of assigning a timer for generation of the access burst during handover. If during the time allocated to the timer expires prior to a successful handover, a handover failure signal is transmitted from the MS to the BTS which then communicates with the BSC for further instruction. A technical advantage of the present invention includes less use of traffic channels during positioning handover. Thus, the load on the network is reduced.

Another technical advantage is that intra-cell handover is performed with less complexity and less time for each TOA positioning request from an MS in idle mode.

BRIEF DESCRIPTION OF THE DRAWINGS

The above features and advantages of the present invention will be more clearly understood from consideration of the following detailed description taken in connection with accompanying drawings in which: Figure 1 illustrates a GSM network in which the present invention may be employed;

Figure 2 shows the logical architecture for TOA positioning method according to one embodiment; Figure 3a portrays channeling while mobile in idle mode;

Figure 3b shows channeling while mobile in dedicated mode;

Figure 4 illustrates signaling during TOA positioning call set-up;

Figure 5 shows the present invention according to one embodiment; and Figure 6 is a signaling diagram illustrating the step for positioning the mobile station using a Time of Arrival (TOA) based positioning method.

Corresponding numerals and symbols in the figures refer to corresponding parts in the detailed description unless otherwise indicated.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

While the making and using of various embodiments of the present invention are discussed in detail below, it should be appreciated that the present invention provides many applicable inventive concepts which can be embodied in a wide variety of specific contexts. The specific embodiments discussed herein are merely illustrative of specific ways to make and use the invention, and do not delimit the scope of the invention.

To better understand the invention, reference is made to Figure 1 , which illustrates a GSM network 10 in which the present invention may be used. The mobile station 12 compπses mobile equipment 22, comprising a terminal such as a cellular telephone, and a Subscriber Identity Module (SIM) 24. The SIM 24 contains an International Mobile Subscriber Identity (IMSI) that identifies the subscriber to the GSM network 10, a secret key for authentication, and other information. Mobile equipment 22 is uniquely identified by the International Mobile Equipment Identity (IMEI). The IMEI and the IMSI are independent, thereby allowing the user personal mobility. The BSS 14 comprises two parts, the Base Transceiver Station (BTS) 26 and the Base Station Controller (BSC) 28. BTS 26 communicates across the standardized Abis interface 30 with BSC 28, allowing operation between components. BTS 26 houses radio transceivers that define a cell and handles the radio-link protocols with the mobile station 12. In a large urban area, there may be a large number of BTSs 26 deployed. BSC 28 manages the radio resources for one or more BTSs 26, and there may be several BSCs 28 within a BSS 14. BSC 28 handles radio-channel setup, frequency hopping, and handovers. BSC 28 provides a connection between the mobile station 12 and the MSC 30 of network Subsystem 16.

The central component of the network subsystem 16 is the Mobile Switching Center (MSC) 30, which acts like a normal switching node of the Public Switched Telephone Network (PSTN), and provides all the functionality needed to handle a mobile subscriber, such as registration, authentication, location updating, handovers, and call routing to a roaming subscriber. These services are provided in conjunction with several functional entities, which together form the network subsystem 16.

The MSC 30 provides the connection to the fixed networks 32 which may include the PSTN or an Integrated Service Digital Network (ISDN), for example. The Home Location Register (HLR) 34 and Visitor Location Register (VLR) 36, together with the MSC 30 provide call routing and roaming capabilities for the GSM network 10. In particular, HLR 34 contains administrative information of the subscriber registered in the corresponding GSM network 10, along with the current location of the mobile station 12. Likewise, the VLR 36 contains selected administrative information from HLR 34 necessary for call control and provisioning of the subscriber services for each mobile currently located in the geographical area controlled by the VLR 36. Other registers are used for authentication and security purposes and the network subsystem 16. The present invention provides a method for positioning of the mobile station 12 within the coverage area of the GSM network 10 or other Public Land Mobile Network (PLMN) that is more efficient than prior art positioning methods. The system for TOA positioning, according to one embodiment of the invention, is shown and denoted generally as 40 in Figure 2. The system 40 is capable of delivering Time Of Arrival (TOA) positioning data for at least one externally operated and maintained requesting agent 54. The requesting agent 54 sends a request for positioning via a Gateway Mobile Location Center (GMLC) 52 which provides an interface for requesting agent 54 to the system 40. The GMLC 52 also contains functionality required to support a Location Services (LCS) function that interacts with other entities within the system 40 to determine the location of the MS 12.

Thus, the GMLC 52 provides the entry node for an external LCS client to use to access the PLMN 46. The GMLC 52 may request routing information from the Home location Register (HLR) 36. After registration authorization, the GMLC 52 sends a positioning request to and receives location data from the VMSC 30. Once the positioning request has been processed by the VMSC 30, the VMSC 30 communicates with the BSC 28 and the Serving Mobile Location Center (SMLC) 50. The SMLC 50 contains the algorithms, methods and systems required to support LCS. The SMLC 50 manages the overall coordination and scheduling of resources required to perform positioning of a the MS 12. It also calculates the final location estimate within a specified level of accuracy.

Furthermore, the SMLC 50 controls a number of LMUs 48 for the purpose of obtaining radio interface measurements to locate or help locate the MS 12 in the area served by the system 40. The SMLC 50 is administered with the capabilities and types of measurement produced by each of its LMUs 48. Although only one LMU 48 is shown in the system 40, at least three such LMUs are used for triangularization of the TOA measurements and subsequent positioning of the MS 12. As such, the LMU 48 is representative of a plurality of LMUs which would normally be used for TOA measurements. Signaling between an SMLC 50 and LMU 48 is transferred via the MSC 30 serving the LMU 48. The measurements returned by an LMU 48 to an SMLC 50 have a generic status in being usable for more than one positioning method.

Alternatively, the functionality of the SMLC 50 and GMLC 52 may be combined in the same physical node, combined in existing physical nodes, or reside in different nodes of the system 40. The SMLC 50 and GLMC 52 are not interconnected, but communications are provided through the VMSC 30. When the VMSC 30 and GMLC 52 are in different PLMNs 46, they are interconnected through an air interface.

With reference to Figure 3a, a positioning handover, depicted generally as 60, according to the prior art, is shown as involving a change from a signaling channel (e.g., Stand Alone Dedicated Channel (SDCCH)) 62 to a first traffic channel (TCH) 64, and then to a second traffic channel 66. During idle mode, a mobile station 12 is assigned a SDCCH 62 within the network 10. A handover of the mobile station 12 is then preformed from the signaling channel to a reserved traffic channel 64. Positioning handover can also occur when the mobile station is placed in dedicated mode, as shown in Figure 3b. In dedicated mode, the traffic channel 64 is already assigned so that assignment to a second traffic channel 66 occurs directly during the handover. Therefore, a second traffic channel 66 is reserved and assigned for positioning handover by the system 40. The access burst 68 generated by the MS 12 during the handover is utilized to provide TOA positioning data for the MS 12.

The entire positioning process as shown in Figure 3a and 3b, portrays the current TOA positioning method. The existing TOA positioning method allows an MS 12 in idle mode to first be assigned a signaling channel (SDCCH) before paging, authentication and ciphering is complete. The SMLC 50 instructs the BSC 28 serving the MS 12 via the MSC 30 to set up a traffic channel 64 (or positioning call set-up). The SMLC 50 then instructs the BSC 28 to perform positioning handover (or fake handover) to another traffic channel 66 for sending handover access burst 68 from the MS 12 to the LMUs 48 utilized for measuring the TOA of the access burst. This method of performing positioning handover is inefficient since it utilizes the resources of two traffic channels, 64 and 66.

As discussed above, the current TOA positioning provides for setting up a positioning call before sending a LCS Information Command message for TOA positioning for a MS 12 in idle mode. Referring now to Figure 4, the signaling sequence during the TOA positioning call set-up for the TOA positioning method of the present invention is shown and denoted generally as 70. Call set-up 70 is initiated (step 72) where the SMLC 50 is adapted to assign a traffic channel 64 which is then communicated to the MSC 30. The assignment of the traffic channel 64 is then verified (step 74) during a message sent from said MSC 30 to the BSC 28.

Upon traffic channel assignment (step 74), channel activation (step 76) is performed by the BSC 28 serving the MS 12 and transmitted to the BTS 26. The BTS 26 is then adapted to send a channel activation acknowledgment to the BSC 28 (step 78). An assignment command is then transmitted from the BSC 28 to the MS 12 (step 80). An establishment indication (step 82) is then performed and sent from the BTS 26 to the BSC 28. Following the establishment indication (step 82), completion of the assignment is performed (step 84) by the MS 12. An assignment traffic channel acknowledgment is then sent from the MSC 30 to the SMLC 50. With reference to Figure 5, a simplified process diagram of the present invention is shown and denoted generally as 90. Essentially, a method of providing Time of Arrival (TOA) positioning data that minimizes the use of traffic channels within the network is illustrated. A signaling channel 62 is assigned to an idle mobile station 12 within the network. A handover 68 of the MS 12 is then performed directly from the signaling channel 62 to a traffic channel 66. The MS 12 is then adapted to generate an access burst during the handover 68, whereas the access burst is utilized to provide TOA positioning data for the MS 12.

The method of the present invention results in saving the assignment of a second traffic channel during positioning handover (68) and therefore reducing the use of the traffic channels within a network. Furthermore, an intra-cell handover to the same channel, or from a signaling channel to a traffic channel without the need for an additional assignment of a second traffic channel is achieved. This results in less complexity of TOA positioning method, less time for each TOA positioning request from an MS in idle mode, and less signals for TOA positioning method.

Figure 6 is a signaling diagram illustrating the step for positioning the MS 12 using a Time of Arrival (TOA) based positioning method, according to one embodiment of the invention. Upon reception of a positioning request from a Location Services (LCS), the Serving Mobile Location Center (SMLC) 50 then transmits (step 105) the LCS information request (TOA) to the Mobile Station Controller (MSC) 30. As such, the SMLC 50 is responsible for carrying out the positioning request. It should be noted that more than one SMLC 50 may be located within each PLMN 46 of the network. Once the MSC 30 receives the LCS information request for TOA positioning, the MSC 30 (step 110) sends a location information command for TOA positioning to the Base Station Controller (BSC) 28 serving said mobile station. The BSC 28 then sends a location information report for TOA positioning to the MS 12 controller 30 (step 115). The location information report for TOA positioning is then transmitted from the mobile station controller 30 to the SMLC 50 (step 120),

Once the SMLC 50 has received an LCS information report for TOA positioning from the MSC 30, an LCS information request is then sent from the SMLC 50 to the MSC 30 (step 125). The LCS information request (step 130) is then transmitted from the MSC 30 to a plurality of Location Management Units 48. The LMUS 48 are responsible for obtaining positioning measurements and providing these measurements to the SMLC 50 for use in calculating location of the MS 12. All communication to and from the LMUS 48 are sent over the air interface. Therefore, each LMU 48 is in wireless communication with an associated Base Station Controller (BTS)

26. The SMLC 50 is responsible for selecting which LMUS 48 should obtain the positioning measurements. As such, it is the SMLC 50 which sends LCS information request messages to each of these selected LMUS 48 (step 130).

Once the LMUS 48 have received the LCS information request (step 130), the BSC 28 is then ready to begin the positioning handover 68 process. A positioning handover occurs when the BSC 28 sends a handover (HO) command message to the MS 12 (step 135), instructing the MS 12 to perform a handover to the serving BTS 26 or a target BTS (not shown) on a specified channel. The handover command message also indicates the TDMA frame number that the MS 12 should begin sending access bursts. When the MS 12 starts sending the access bursts in the handover access message (step 145), the LMUs 48 make their a Time of Arrival (TOA) measurements of the access burst. Since the handover is a positioning handover and not a radio- related handover, the BTS 26 will not respond to the handover access message, and the MS 12 will stop sending the access burst upon the expiration of a timer (step 150) within the MS 12. Thereafter, the MS 12 returns to the old channel that it was assigned to, and sends a handover failure message to the BSC 28 (step 155).

The TOA measurements are forwarded via a LCS information response (step 165) from the LMUS 48 to the SMLC 50 for use in assisting the calculation of the geographical location of the MS 12. After the SMLC 50 calculates the location of the MS 12, this location is transmitted to the LCS client that requested the positioning. It should be noted that the requesting client could be located within the MS 12, within the MSC 30 or could be in external node 54 such as an Intelligent Location (IN) node. Once the LCS has received the requested information, an acknowledgment of location performance is transmitted (step 170) from the SMLC 50 to the MSC 30.

While this invention has been described with a reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications and combinations of the illustrative embodiments as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to the description. It is, therefore, intended that the appended claims encompass any such modifications or embodiments.

Claims

WHAT IS CLAIMED IS:

1. In a wireless communications network, a method of providing Time of Arrival (TOA) positioning data that minimizes the use of traffic channels within the network, said method comprising the steps of: assigning a signaling channel to an idle mobile station within the network; causing a handover of said mobile station directly from said signaling channel to a traffic channel; causing said mobile station to generate an access burst during said handover; and utilizing said access burst to provide TOA positioning data for said mobile station.

2. The method according to Claim 1 wherein said assigning step is performed by causing a Base Station Controller (BSC) serving said mobile station to perform a handover from said signaling channel to said traffic channel.

3. The method according to Claim 2 wherein said assigning step is performed by causing a Serving Mobile Location Center (SMLC) in communication with said BSC to instruct said BSC serving said mobile station to perform a handover after a specified period of time.

4. The method according to Claim 3 wherein said assigning step is performed by transmitting a positioning handover instruction to said BSC via said MSC.

5. The method according to Claim 1 wherein said step of causing said mobile station to generate an access burst is performed by sending a handover access burst from said mobile station to the configured Location Management Units (LMUs) for TOA measurement.

6. In a wireless communications network, a method of providing Time of Arrival (TOA) positioning data for a Mobile Station (MS), said network having a Serving Mobile Location Center (SMLC) communicably coupled and adapted to instruct a Base Station Controller (BSC) serving said MS via a Mobile Station Controller (MSC), said method comprising the steps of: causing a Location Services (LCS) Information Request (TOA) to be transmitted from said SMLC to said MSC; causing a Location Information Command (TOA) to be generated and transmitted from said MSC to said BSC; causing a LCS Information Request to be transmitted from said MSC to a plurality of Location Management Units (LMUs) adapted to measure TOA access bursts generated by said MS; assigning a Stand Alone Dedicated Control Channel (SDCCH) to said MS; transmitting a handover command to said MS; performing a handover of said MS from said SDCCH to a traffic channel; and causing said MS to generate an access burst during said handover step so that said plurality of LMUs can measure the TOA of said access burst for positioning said MS.

7. The method according to Claim 6 wherein said step of causing a Location Information Command (TOA) to be generated and transmitted from said MSC to said BSC further comprises the step of reporting Location Information (TOA) to said MSC.

8. The method according to Claim 7 wherein said reporting step is followed by the step of sending a LCS Information Report (TOA) from said MSC to said SML.

9. The method according to Claim 6 wherein said method further comprises the step of requesting LCS Information from said MSC.

10. The method according to Claim 10 wherein said sending step is followed by the step of relaying a LCS Information Response from said plurality of LMUs to said MSC.

11. The method according to of Claim 11 wherein said relaying step is followed by the step of performing a location acknowledgment, said location acknowledgment performed by said SMLC.

12. The method according to Claim 6 wherein said transmitting step is accompanied by the step of assigning a timer to said handover for use in TOA positioning.

13. The method according to Claim 14 wherein said step of assigning a timer is followed by causing a handover signal to be transmitted to said plurality of LMUs upon expiration of said timer.