WO2003085995A1

WO2003085995A1 - Methods and apparatus for robust paging in wireless systems

Info

Publication number: WO2003085995A1
Application number: PCT/US2003/009610
Authority: WO
Inventors: Vincent Park; George Tsirtsis; Michaela Catalina Vanderveen
Original assignee: Flarion Technologies, Inc.
Priority date: 2002-04-02
Filing date: 2003-03-31
Publication date: 2003-10-16
Also published as: AU2003226119A1

Abstract

Methods and apparatus for improving the robustness of paging in wireless networks by defining separate signaling (502) and boundary paging areas (504) are described. Each boundary paging area (504) is a region used to control mobile node registration with a paging agent (506. There is a corresponding larger signaling paging area (502) into which paging signals are transmitted for each boundary paging area (5049. Signaling paging areas (502) normally have some overlap. Since the signaling paging area (502) is larger than the corresponding boundary paging area (504) a mobile node (510) may travel into a region into which it is supposed to register with a new paging agent (506), e.g., into a new boundary paging area (504), but still receive paging signals from the paging agent (506) with which it was just previously registered. Thus, failure to promptly detect entry into a new paging (504) area and to promptly register does not result in the loss of the ability to page a mobile node 510).

Description

METHODS AND APPARATUS FOR ROBUST PAGING IN WIRELESS SYSTEMS

RELATED APPLICATIONS:

The present application claims the benefit of the filing date of U.S. Provisional Patent

Application S.N. 60/369,399, filed April 2, 2002 which has the same title as the present application and which is hereby expressly incorporated by reference.

FIELD OF THE INVENTION:

The present invention is directed paging systems in a communications system and, more particularly, to methods and apparatus for robust paging in wireless systems.

BACKGROUND:

Typically, paging is used to allow mobile communication devices, hereinafter generically referred to as mobile nodes, to conserve battery power by entering a dormant or idle mode during which the communication capability of the mobile node is significantly reduced.

In the context of this document, paging refers to any mechanism used to locate, alert and/or re- activate a dormant or idle mobile communication device through the use of transmitted signals, e.g., a page.

In general, a mechanism for paging mobile nodes is coupled with a mechanism for mobile nodes to register for paging support. There are many different strategies for registration and paging. Typically, the registration process associates the mobile node with a particular "paging area" that comprises a subset of the base stations, cells and/or sectors of a wireless communication network and a "paging agent" that is responsible for attempting to page the dormant mobile node within the paging area when needed. When the paging agent receives an indication that a dormant mobile node must be paged, the paging agent sends page signaling throughout the corresponding paging area. As a dormant mobile node migrates between paging areas, re-registration or a location update is required to associate the mobile node with the particular paging area in which the mobile should be paged. Typically, a mechanism is provided by which the mobile node may detect when it departs from the paging area for which it has registered,. so that it can re-register for paging support throughout a new paging area. The area throughout which a mobile node may migrate without re-registration and the area throughout which a page will be signaled normally coincide, i.e., they are usually the same size.

If a mobile node migrates out of its registered paging area and fails to re-register in the new paging area, attempts to page the dormant mobile node that are directed to the most recently associated paging area will fail.

Thus, in existing systems if a mobile node leaves the paging area in which it is registered and enters another paging area without registering in the new paging area, the mobile may become unreachable for a period of time. Failure to register in a new paging area in a timely manner may be the result of the mobile node's failure to promptly detect entry into a new paging area and/or for other reasons, e.g., communications delays that interfere with the registration process.

It would be desirable if the chance of being unable to contact a mobile node because it has entered a new paging area and not yet registered with the paging agent in the new paging area could be reduced. In view of the above discussion, it is clear that a need exists for a better implementation and method of paging, in order to improve paging success rates.

BRIEF DESCRIPTION OF THE FIGURES:

Figure 1 illustrates an exemplary access node, e.g., base station and/or access router implemented according to this invention.

Figure 2 illustrates an exemplary end node, e.g., mobile node implemented according to this invention.

Figure 3 illustrates an exemplary paging agent implemented according to this invention.

Figure 4 illustrates an exemplary communications system of the invention that includes a paging agent and a signaling paging area that encompasses a boundary paging area. Figure 5 illustrates an exemplary communications system including two adjacent and overlapping signaling paging areas each of which fully encompasses one of two illustrated non- overlapping boundary paging areas in accordance with the present invention.

SUMMARY OF THE INVENTION:

The present invention is directed to methods and apparatus for improving the robustness of paging in a wireless network and increasing the success rate of paging attempts.

In order to provide the paging improvement of the present invention, a novel distinction is made between a first paging area used for boundary detection, referred to herein as a boundary paging area, and a second paging area referred to herein as a signaling paging area. Detecting a boundary of a boundary paging area causes mobile nodes to register their new location. Thus, boundary paging areas serve as paging registration areas since they are used to control paging registration. The signaling paging area, however, is the area into which paging signals are transmitted, e.g., to locate, alert and/ or re-activate a dormant mobile node. Normally there is one boundary paging area corresponding to each signaling paging area. In accordance with the present invention, the boundary paging area is normally a subset of the corresponding signaling paging area.

Communication systems in accordance with the present invention may include novel hardware and/ or software implementing the invention within the access nodes, e.g., base stations or access routers, paging agents, and mobile nodes (MNs), e.g., mobile terminals. The unique hardware and/or software used by such systems may perform functions including: (1) identifying, modifying and/or controlling boundary paging areas, (2) identifying, modifying, and/or controlling signaling paging areas, (3) storing and using user/mobile node session information, boundary paging area identifiers / state and signaling paging area identifiers / state, (4) signal processing, and (5) performing message generation, and/or transmission.

Various implementations of the present invention may include non-overlapping paging areas, overlapping paging areas, statically configured paging areas, and dynamically configured paging areas. By utilizing the unique features, novel area definitions, method and/or apparatus of the present invention, the efficiency and success rate of paging may be increased, particularly as the mobile node migrates, as compared to known systems where the signaling and boundary paging areas are the same. The present invention may be particularly useful and advantageous in system implementations where reduced communications overhead has been achieved by compressing the paging area information provided to the mobile node, which the mobile node uses to determine paging area crossing.

Additional features, embodiments and benefits of the present invention are discussed in the detailed description which follows.

DETAILED DESCRIPTION:

The following describes methods and apparatus for improving the robustness and success rate of paging attempts. This is achieved primarily by making a distinction between (1) the paging area used for boundary detection that triggers registration and/or re-registration and (2) the paging area into which paging signals are transmitted, e.g., to locate, alert and/or re-activate a dormant mobile node. In the subsequent discussion we will refer to the first area as the boundary paging area (BPA) and the second area as the signaling paging area (SPA). A paging area comprises a set of individual coverage areas, e.g. base station cells or sectors. As discussed above, in known systems, no distinction is made between the BPA and SPA, thus they are effectively the same, hi accordance with the present invention, by extending the SPA, e.g., by including additional base stations, cells and/or sectors, such that it is larger than the BPA, i.e., (SPA>BPA) the robustness of paging is improved. Normally, there is one SPA corresponding to each BPA with the SPA encompassing the full corresponding BPA.

Fig. 1 illustrates an exemplary access node 12, e.g., base station and/or access router, implemented in accordance with the invention. The base station 12 includes antennas 203, 205 and corresponding receiver, transmitter circuitry 202, 204, respectively. The receiver circuitry 202 includes a decoder 233 while the transmitter circuitry 204 includes an encoder 235. The circuitry 202, 204 is coupled by a bus 230 to an I/O interface 208, processor 206, e.g., CPU, and memory 210. The receiver's antenna 203 and the transmitter's antenna 205 couple the base station 12 to other nodes, e.g., mobile nodes via wireless links. The I/O interface 208 couples the base station 12 to other network nodes via, e.g., the Internet. The memory 210 includes routines, which when executed by the processor 206, cause the base station 12 to operate in accordance with the invention. Memory includes communications routines 223 used for controlling the base station 12 to perform various communications operations and implement various communications protocols. The memory 210 also includes a base station control routine 225 used to control the base station 12 to implement the method of the present invention. The base station control routine 225 includes a paging module 222 used to control paging in accordance with the present invention. Memory 210 also includes information 212 used by communications routines 223, and control routine 225. The information 212 includes an entry for each active mobile station user: User 1 /MN information 213, User N/ MN information 213' which lists the active sessions being conducted by the user and includes information identifying the mobile node, e.g., mobile terminal (MT), being used by a user to conduct a communications session. Information 212 also includes boundary paging area identifiers 214 and signaling paging area identifiers 215 in accordance with the novel features of the present invention. The information 212 may also include information associating various boundary and/or signaling paging areas with one or more paging agents wliich control paging signals transmitted into the SPAs identified by information 215 and with which mobile nodes register when in the BPA's identified by information 214.

Figure 2 illustrates an exemplary mobile node 14 implemented in accordance with the present invention. The mobile node 14 may be used as a mobile terminal (MT). The mobile node 14 includes receiver and transmitter antennas 303, 305 wliich are coupled to receiver and transmitter circuitry 302, 304 respectively. The receiver circuitry 302 includes a decoder 333 while the transmitter circuitry 304 includes an encoder 335. The receiver's antenna 303 and the transmitter's antenna 305 couple the mobile node 14 to other nodes, e.g., base station 12 via wireless links. The receiver and transmitter circuits 302, 304 are coupled by a bus 305 to a memory 310 and a processor 306, e.g., CPU. Processor 306, under control of one or more routines stored in memory 310 causes the mobile node 14 to operate in accordance with the methods of the present invention, hi order to control mobile node operation, memory 310 includes communications routine 323, and mobile node control routine 325. The communications routine 323 is used for controlling the mobile node 14 to perform various communications operations and implement various communications protocols. The mobile node control routine 325 controls the operation and signaling, including paging area registration signaling, performed by the mobile node 14 in accordance with the methods of the present invention and performs the steps described in regard to mobile node operations. The memory 310 also includes user/device/session /resource information 312 which may be accessed and used to implement the methods of the present invention and/or data structures used to implement the invention. Memory 310 also includes boundary paging area information 313 which according to this invention allows mobile node 14 to recognize when it crosses a paging boundary.

Fig. 3 illustrates an exemplary Paging Agent 16 implemented in accordance with the invention. The paging agent is normally coupled to one or more base stations in the SPA or SPAs into which the paging agent controls the transmission of paging signals. The 17O interface 408 couples the paging agent 16 to other network nodes, e.g., base station 12. The I/O Interface 408 is coupled by a bus 430 to a processor 406, e.g., CPU, and memory 410. The memory 410 includes routines, which when executed by the processor 406, cause the paging agent 16 to operate in accordance with the invention. Memory 410 includes communications routines 423 used for controlling the paging agent 16 to perform various communications operations and implement various communications protocols. The memory 410 also includes a paging agent control routine 425 used to control the paging agent 16 to implement the steps of the method of the present invention described herein. The paging agent control routine 425 includes a paging agent module 422 used to control paging for mobile nodes according to the method of the present invention. Memory 410 also includes information 412 used by communications routines 423, and control routine 425. The information 412 includes an entry for each pageable mobile station user: User 1 / MN information 413, User N MN information 413' registered with the paging agent 16. Information 412 also includes signaling paging area state 415 in accordance with the novel features of the present invention. The signal paging area state information 415 may be used to identify cells, base stations and routers, to which the paging agent 16 communicates to control the paging activity to mobile nodes registered with the paging agent. The Information 412 may also include boundary paging area state information 417. The boundary paging area state information 417 may be used in embodiments of the present invention where the boundaries are dynamically reconfigured. New boundary paging information may be generated and stored in the paging agent 16, e.g., in response to a new cell being added to the communications system or a cell being removed from the system. Some or all of the new BPA and SPA state is transmitted to the access nodes and/or base stations 12 as required, e.g., to update the BPA and/or SPA information stored therein. Servers and/or host devices which may be included in the communication system of the present invention may be implemented using circuitry which is the same as, or similar to, the circuitry of the exemplary access node, e.g., base station and/or access router shown in Fig. 1 but with interfaces and/or control routines suited to the particular server/host device's requirements. The control routines and/or hardware in such servers and/or hosts cause the devices to implement the described methods of the present invention.

Figure 4 illustrates an exemplary wireless communication system implemented in accordance with the present invention. Fig. 4 depicts the wireless coverage, e.g., transmission area, provided by a plurality of base stations. The transmission areas may be cells and/or sectors. Each cell normally includes a plurality of mobile nodes 510, e.g., cellular phones or notebook computers equipped with wireless receiver/transmitters. Each hexagon shape depicts a coverage area 501 of one base station. The base station may be the same as, or similar to, the base station 12 of Fig. 1. Each base station 12 is assumed to be located inside the cell coverage area 501. A boundary paging area (BPA) 504, designated through the use of circles for shading, is shown as the union of a set of transmission areas inside the innermost dark solid line shown in Fig 4. Mobile nodes, e.g., mobile node 510 within the BPA 504 register with a paging agent 506 and are to re-register with the same or possibly another paging agent upon leaving BPA 504. Mobile node 510 may be implemented as shown in Fig. 2. Arrow 520 represents mobile node 510 leaving BPA 504. In accordance with the invention, signaling paging area (SPA) 502, designated using diagonal lines for shading, fully includes BPA 504 and is the union of the transmission areas inside the outermost dark solid line shown in Fig 4. Accordingly, even though mobile node 510 has left BPA 504 and should re-register with the same or another paging agent, it remains in SPA 502. Accordingly, while it remains in SPA 502, mobile node 510 may still receive paging signals from the paging agent with which it last registered, thereby reducing the risk of missing paging signals due to a brief delay in re-registering upon leaving BPA 504. This is because paging agent 506, which is the same as or similar to paging agent 16 of Fig 3, will page into the whole of the area covered by SPA 502 if necessary to contact mobile node 510. Dashed lines 508, 509 are used to figuratively illustrate that the paging agent 506 is coupled to the cells in the whole of SPA 502 and controls the paging in that area 502. The paging agent 506 may, in addition, be coupled to and control paging in other areas. In fact, paging areas may be dynamically changed, e.g., when cells are deleted and/or added. In cases where a mobile node fails to detect that it has migrated beyond the BPA, e.g., as defined by information stored in the mobile node or transmitted thereto, or when detection of this condition is delayed, the mobile node may still be paged provided it is within the SPA associated with the BPA in which the node is registered. The degree to which the SPA is extended beyond the BPA is a system design choice and is dependent on other factors such as the boundary detection mechanism and its failure modes, hi various embodiments at least a portion of the SPA extends beyond the BPA by the minimum transmission range, e.g., radius, of a base station or one of its sectors. This corresponds, in many cases to the minimum radius of a cell. In other cases, the SPA extends beyond the BPA by at least the minimum diameter of a cell.

Figure 5 depicts an exemplary communications system 503 including two SPAs 502, 502' represented using diagonal lines of different slopes for shading each of the two areas 502, 502'. System 503 also includes two corresponding BPAs 504, 504'. BPA 504 is identified using circles for shading while BPA 504' includes triangles for shading. The area inside the boundary created by line 602 illustrates the overlapping portion of coverage between the two SPAs 502, 502' while the line 604 illustrates the non-overlapping border between the two BPAs 504, 504'. In the system depicted in Fig 5, two or more paging agents may be used to control paging. The paging agents may be the same as, or similar to, paging agent 16 of Fig 3. The first paging agent may control paging within SPA 502 and the second paging agent may control paging within SPA 502'. Alternatively, a single paging agent may control paging in both SPA's 502, 502' with mobiles registering with the paging agent each time they enter a different BPA 504, 504'. Mobile nodes similar to mobile node 14 of Fig 2 may move throughout the system. In various embodiments, located within each transmission area 501, e.g., cell or sector, it is a base station 12 or antenna coupled to a base station 12.

As in the Figure 4 and 5 examples, it is often convenient to make the SPA larger than the BPA by a distance or area corresponding to one or more base stations, cells, and/or sectors beyond the area of the BPA. hi some embodiments, the SPA exceeds the size of the BPA by a consistent relatively uniform amount. In other embodiments, the amount by which the SPA exceeds the corresponding BPA will vary depending on a host of factors such a geographic conditions, the number of base stations, cells, and/or sectors in a region, node mobility patterns, etc.

In one embodiment of a wireless communication network based on the invention the amount by which SPAs exceed BPAs throughout the entire system is uniform for all paging areas, while in another embodiment the amount by which SPAs exceed BPAs varies for individual paging areas. Accordingly, one exemplary wireless communication network comprises a plurality of paging areas, wherein the SPA exceeds the corresponding BPA in size for each paging area but by differing amounts.

The method and apparatus of the invention described above are applicable to many different paging area designs and systems. In particular, it is applicable for both non-overlapping and overlapping paging areas that are either statically or autonomously configured, hi the case of systems which use non-overlapping paging areas, the boundary paging areas remain non- overlapping, while the signaling paging areas are intentionally extended and thus become overlapping.

The methods and apparatus described herein may be particularly useful in support of paging systems where the paging area description and/or boundary detection mechanisms make use of information compression techniques.

For example, in some paging system designs the mobile node is provided with a list of identifiers for all the wireless network access nodes that comprise a paging area. As the mobile node migrates, it associates with different local wireless access nodes based on some criteria such as received signal strength. Boundary detection is achieved by comparing the identifier advertised by the currently associated wireless access node with the previously provided list of identifiers that comprise the paging area. To reduce communication overhead in such schemes, it may be desirable to compress the paging area list provided to the mobile node. A consequence of the compression maybe a non-zero probability of the mobile node failing to detect that the identifier of an associated wireless access node is not part of the paging area list, h such cases, if the signaling paging area does not extend beyond the boundary paging area as described herein, the mobile node may not be reachable and thus may miss a page, e.g., as a result of a mobile node's failure to detect leaving the BPA. The methods and apparatus of the present invention are not limited by the purpose of a page and any subsequent action required by a mobile device or any associated computing equipment or software that may be implied by the reception of a page. The methods and apparatus of the present invention, are applicable to a wide range of communications systems including, e.g., OFDM systems, CDMA systems, and various other types of cellular and non-cellular systems which support the use of IP for communications purposes.

hi various embodiments nodes described herein are implemented using one or more modules to perform the steps corresponding to one or more methods of the present invention, for example, signal processing, message generation and/or transmission steps. Thus, in some embodiments various features of the present invention are implemented using modules. Such modules may be implemented using software, hardware or a combination of software and hardware. Many of the above described methods or method steps can be implemented using machine executable instructions, such as software, included in a machine readable medium such as a memory device, e.g., RAM, floppy disk, etc. to control a machine, e.g., general purpose computer with or without additional hardware, to implement all or portions of the above described methods, e.g., in one or more nodes. Accordingly, among other things, the present invention is directed to machine-readable medium including machine executable instructions for causing a machine, e.g., processor and associated hardware, to perform one or more of the steps of the above-described method(s).

Numerous additional variations on the methods and apparatus of the present invention described above will be apparent to those skilled in the art in view of the above description of the invention. Such variations are to be considered within the scope of the invention. The methods and apparatus of the present invention may be, and in various embodiments are, used with CDMA, orthogonal frequency division multiplexing (OFDM), and/or various other types of communications techniques which may be used to provide wireless communications links between access nodes and mobile nodes. In some embodiments the access nodes are implemented as base stations which establish communications links with mobile nodes using OFDM and/or CDMA. In various embodiments the mobile nodes are implemented as notebook computers, personal data assistants (PDAs), or other portable devices including receiver/transmitter circuits and logic and/or routines, for implementing the methods of the present invention.

Claims

What is claimed is:

1. A communications system comprising: a first boundary paging area; and a first signaling paging area, said first signaling paging area being larger than and including said first boundary paging area.

2. The communications system of claim 1, further comprising: a first paging agent associated with said first signaling paging area for controlling the transmission of paging signals in said first signaling paging area.

3. The communications system of claim 2, further comprising: a mobile node, said mobile node including means for registering with said first paging area upon entry into said first boundary paging area.

4. The communications system of claim 2, wherein said first signaling paging area corresponds to a first plurality of cells; and wherein said first paging agent is coupled to at least one base station in each of said first plurality of cells to control the transmission of paging signals by said base stations into the first signaling paging area.

5. The communications system of claim 2, further comprising: a second boundary paging area; and a second signaling paging area, said second signaling paging area being larger than and including said second boundary paging area.

6. The communications system of claim 5, wherein said second signaling paging area overlaps a portion of said first signaling paging area.

7. The communication system of claim 6, wherein the first and second boundary paging areas are non-overlapping areas.

8. The communications system of claim 7, wherein said first and second boundary paging areas include overlapping areas.

9. The communication system of claim 6, wherein said second signaling paging area corresponds to a second plurality of cells; and wherein said second paging agent is coupled to at least one base station in each of said second plurality of cells.

10. The communications system of claim 9, wherein at least one of the cells in the first and second plurality of cells is common to both the first and second plurality of cells.

11. The communication system of claim 5, wherein said first and second boundary paging areas are static.

12. The communications system of claim 5, wherein said first and second boundary paging areas are dynamically configured during system operation thereby allowing said first and second boundary paging areas to include different cells at different times of system operation.

13. The communications system of claim 5, wherein the first signaling paging area extends beyond the first boundary paging area, by the diameter of at least one communications cell, at least one location.

14. A communication method for use in a communications system including a mobile node, a first boundary paging area, a first signaling paging area, and a first paging agent used to control the transmission of paging signals into said first paging signaling area, the first signaling paging area being larger than and including said first boundary paging area, the method comprising the steps of: transmitting a paging signal to said mobile node while said mobile node is registered with said first paging agent and within said first boundary paging signaling area at a location which is outside said first boundary paging area.

15. The communication method of claim 14, wherein said communications system further includes a second boundary paging area and a second paging agent, the method comprising: operating said mobile node to detect that it has moved into the second boundary paging area; and operating said mobile node to transmit a paging registration message to said second paging agent in response to detecting that said mobile node has moved into the second boundary paging area.

16. A paging method for use in a mobile communications system including a mobile node and a plurality of signaling paging areas, the system including a corresponding boundary paging area located within each of the signaling paging areas, the method comprising: storing registration information associating a mobile node with a first paging signaling area; operating the mobile node to detect when the mobile node leaves a first boundary paging area corresponding to said first paging signaling area and enters a second boundary paging area corresponding to a second signaling paging area; transmitting a paging signal directed to said mobile node into said first signaling paging area while said mobile node is in said second boundary paging area; and operating the mobile node to receive said transmitted paging signal.

17. The paging method of claim 16, further comprising the step of: operating the mobile node to transmit registration information to a paging agent used to control paging into said second signaling region in response to detecting entry into the second boundary paging area.

18. A communications system, comprising: a paging agent, said paging agent including: i) stored information defining a plurality of overlapping first paging areas into which paging signals are transmitted under control of said paging agent; and ii) stored information defining a plurality of non-overlapping second paging areas, one second paging area being included in each of said first paging areas, said non-overlapping second paging areas defining mobile node paging registration areas.

19. The communications system of claim 18, wherein said paging agent further includes: iii) means for modifying at least some of said first and second paging areas in response to the addition of a new communications cell to said system; and iv) means for transmitting modified first paging area information to at least some base stations included in a modified first paging area.

20. The communication system of claim 19, wherein said paging agent further includes: v) means for transmitting modified second paging area information to at least some mobile nodes included in a modified second paging area included within said modified first paging area.

21. The communications system of claim 19, further comprising: a plurality of base stations coupled to said paging agent, said base stations receiving and storing said transmitted modified first paging area information.

22. The communications system of claim 21, further comprising: a plurality of mobile nodes coupled to said paging agent by at least one of said plurality of base stations, said nodes receiving and storing at least some of said modified second paging area information.

23. The communications system of claim 19, wherein said modified first paging area information includes information identifying base stations corresponding to said modified first paging area.

24. The communications system of claim 21, wherein said second paging area information includes information identifying base stations included in said modified second paging area.

25. The communications system of claim 24, wherein said first paging area is a signaling paging area and said second paging area is a registration paging area.