Handover in a hybrid communications network

Handover in a hybrid communication network

CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority from U.S. Provisional Application No. 60/379,958 filed on March 10, 2002, which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION I. Technical Field The present invention generally relates to wireless communication, and more particularly, to a method and apparatus for providing continuous connection when a mobile phone moves from one base station to another base station.

II. Related Fields Code Division Multiple Access (CDMA) modulation is just one of several technologies that facilitate communication in which there are many system users. Although there are other amplitude modulation schemes such as time division multiple access (TDMA), frequency division multiple access (FDMA), global digital mobile phone system (GSM), amplitude companding single sideband (ACSSB) and other amplitude modulation schemes, orthogonal frequency division multiplexing ( Technologies such as OFDM and Integrated Distribution Advanced Network (iDEN) are available, and CDMA has significant advantages over these other modulation technologies. The use of CDMA technology in multiple access communication systems is in the serial number 4,901,307, and the invention name is "Spread Spectrum Multiple Access Communication System Using Satellite OrTerrestrial". Repeaters (spread spectrum multiple access communication system using artificial satellites or terrestrial transponders)" is disclosed in the US patent, which is assigned to the assignee of the present invention, and the content of its disclosure is incorporated herein by reference. The serial number is 4,901,307 The U.S. patent describes multiple access technology, in which a large number of mobile phone system users use code division multiple access (CDMA) spread spectrum communication signals to communicate through satellite transponders or ground base stations (also called cell base stations or cell sites). Each user has a transceiver. When using CDMA communication, the spectrum can be used repeatedly, which allows the increase of system user capacity. Using CDMA technology can achieve much higher spectrum efficiency than using other multiple access technologies.

In a conventional cellular phone system, when analog frequency modulation (FM) technology is used, the available frequency band is divided into channels with a bandwidth of usually 30KHz. The system service area is geographically divided into cells of various sizes. The available frequency channels are divided into groups, and each group usually contains an equal number of channels. The frequency groups are allocated to cells in a way that minimizes the probability of co-channel interference. For example, imagine a hexagon with seven frequency groups and the cells are of equal size. The frequency group used for a cell will not be used for the six nearest or surrounding neighboring cells of the cell. In addition, the frequency group of a cell will not be used for the twelve sub-adjacent units around the cell.

A more difficult situation occurs when the mobile station is moved to a cell served by a base station from another cellular system. A complicating factor in handover between systems is that neighboring cellular systems often have different characteristics and requirements. For example, neighboring cellular systems often work on different frequencies and may maintain different levels of base station output power, pilot strength, or capacity. Moreover, neighboring cellular systems may require different messaging structures, even for similar types of messages or their functionality. For example, the so-called GSM standard does not have a mechanism for soft handover. Therefore, using the error interface to switch calls from the CDMA network to the GSM network is problematic, and vice versa.

One way to deal with this problem is to modify GSM so that it can be switched to a non-GSM system (such as a CDMA system). Another way to deal with this problem is to modify CDMA so that it can handle the standard mechanism in the traditional GSM system. However, CDMA and GSM are relatively well-established systems, and operators and equipment providers are reluctant to make expensive modifications to existing equipment in order to adapt them to neighboring incompatible systems. If new messages are added to the error interface to support dual-mode mobile stations, then modifications must be made to use existing hardware to support these new messages. Frankly speaking, this is reluctant from the point of view of operators and equipment providers.

Summary of the invention

The present invention solves the problems discussed above.

One aspect of the hybrid communication system is to seamlessly integrate the standard GSM network into the standard CDMA network. This can be achieved by using a hybrid mobile switching node (MSN) that supports internal working functions between a CDMA-compatible radio access network (RAN) and a GSM core network. The hybrid MSN can be connected to standard GSM core network entities, such as GSM Location Home Register (HLR), Authentication Center (AuC) and Short Message Service Center (SMSC), etc. Therefore, the system built around the standard CDMA error interface will not require changes to the CDMA-based RAN and GSM core network. Such a system consists of dual-mode mobile stations that can connect to a standard GSM Subscriber Identity Module (SIM) and respond to GSM authentication procedures.

Correspondingly, the embodiments of the present invention provide an apparatus and method for realizing handover of a mobile station in a first wireless communication system and a second wireless communication system. The first wireless communication system has a first mobile station operable by a first base station. A second mobile switching node operable by the switching node and the second base station. In the embodiment, the first wireless communication system is a CDMA-based system, and the second wireless communication system is a GSM-based or iDEN-based system. It is also expected that the second wireless communication system will be an OFDM-based system.

The handover message is required to be received at the first mobile switching node. The handover request message is sent from the first mobile switching node to the second mobile switching node. A message from the second mobile switching node is sent to request the allocation of a handover. In an embodiment, this message is sent to the VLR of the second wireless communication system. In response to this, the second mobile switching node receives the handover request confirmation message. The handover request confirmation message is then sent from the second mobile switching node to the first mobile switching node. The initial address information is sent to start the circuit connection between the first mobile switching node and the second mobile switching node. Then, the call is received from the first mobile switching node.

A signal identifying that the circuit used for the call has been reserved from the second mobile switching node is sent to the first mobile switching node. Upon receipt, a handover execution message is sent from the first mobile switching node. The message that the handover has started is received at the first mobile switching node, and the first mobile switching node then sends a handover complete message.

The above and further features of the present invention will be stated together with the features and advantages in the appended claims, so these features will become clearer by considering the following detailed description of exemplary embodiments of the present invention with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings: Figure 1 illustrates a diagram of a hybrid cellular system.

Figure 2 illustrates the interfaces in a network of multiple MSNs and base stations (BS).

Figure 3A illustrates the direct switching application part (DTAP) data structure.

Figure 3B illustrates the base station subsystem management application part (BSSMAP)/base station mobile application part (BSMAP) data structure.

Figure 3C illustrates the base station subsystem-application protocol data unit (BSS-APDU) data structure.

Figure 4 illustrates the signaling in the inter-MSN handover.

Figure 5 illustrates the basic switching process without a circuit connection.

Figure 6 illustrates the signaling of a successful subsequent inter-MSN handover.

Figure 7 illustrates the signaling of the subsequent handover from MSN-B to MSN-C that requires a circuit connection between MSN-A and MSN-C.

Figure 8 illustrates the call flow chart of the switching procedure from MSN-B to MSN-C without the need for a circuit connection between MSN-A and MSN-C.

detailed description

FIG. 1 is a diagram of an exemplary cellular telephone system 100. As shown in FIG. The information shown can use any of a variety of multiple access modulation techniques to facilitate communication between mobile stations or mobile phones and base stations in the usual large number of systems. This multiple access communication system technology includes: Time Division Multiple Access (TDMA), Global Digital Mobile Phone System (GSM), General Packet Radio Service (GPRS), High-speed Circuit Switched Data (iDEN), Frequency Division Multiple Access (FDMA), Code Division Multiple Access (CDMA), TS Code Division Multiple Access (TSCDMA), Orthogonal Frequency Division Multiplexing (OFDM), and amplitude modulation schemes such as amplitude companding single sideband.

For the sake of illustration, Figure 1 describes the communication system as a combination of a CDMA-based system and a GSM-based system. It should be understood that any two communication systems may be used, such as the communication systems discussed above.

The mobile station 104 exemplifies a GSM/GPRS device with a subscriber identification module 106. The mobile station 108 exemplifies a GSM/CDMA2001x device with a subscriber identification module 110. The mobile station 108 can be equipped with hardware and/or software modified from a traditional GSM or CDMA mobile station, so that the device can interface with both GSM and CDMA architectures. The mobile station 112 exemplifies a CDMA2000 1x device with a subscriber identification module 114.

The mobile stations 104, 108, and 122 are wireless communication devices, such as mobile phones, personal digital assistants, computers, or other wireless devices capable of wireless communication of voice or data information. The SIM cards 106, 110, and 114 may be standard GSM SIM cards. The standard GSM SIM card can be operated in a CDMA 1x mobile phone and can receive and respond to signals from base stations in the CDMA and GSM cellular systems. The combination of such a GSMSIM card 108 and a CDMA1x mobile phone is discussed in U.S. Patent Provisional Application No. 60/350,829 filed on January 17, 2002 and U.S. Patent Provisional Application No. 60/354,086 filed on February 1, 2002. Both of these provisional applications were transferred to U.S. Patent Application No. 10,076,831 on February 14, 2002, were assigned to the same patent assignee as this application, and are specifically incorporated herein by reference. The SIM cards 106, 110, and 114 may also be dedicated SIM cards configured to operate in more than one wireless communication system.

The mobile station 104 may be communicatively coupled with a radio access network (RAN) 116. In one embodiment, the RAN 116 is a standard GSM or GSM/GPRS RAN, and includes a standard GSM-based base transceiver subsystem (BTS) and a standard GSM base station controller (BSC) (not shown).

The mobile stations 108 and 112 may be communicatively coupled with a radio access network (RAN) 120. The mobile station 108 may be communicatively coupled with the RAN 116 and the RAN 120 at the same time. In one embodiment, RAN 120 is a CDMA1x RAN as described in U.S. Provisional Patent Application No. 60/340,356 filed on December 14, 2001, which was converted to the United States on February 14, 2001. Patent Application No. 10/077,556, is assigned to the same patent assignee as this application, and is specifically incorporated herein by reference. The RAN 120 is a standard CDMA2000 or CDMA2000 1x RAN, and includes a standard CDMA-based base transceiver subsystem (BTS) and a standard CDMA-based base station controller (BSC) (not shown).

The GSM RAN 116 is coupled to the GSM SMSC/SGSN 124 through the A-interface 128. The GSM SMSC/SGSN 124 is coupled to the GSM switching network 132 using mobile application (MAP), integrated services digital network user part (ISUP) and GPRS tunneling protocol (GTP) interfaces and protocols.

The CDMA RAN 120 is coupled to the GSM1x mobile switching node (MSN) 132 through a standard IOS4 interface/protocol 136. The MSN 132 is preferably a hybrid MSN and is coupled to the RAN 112 and the GSM switching network 136 at the same time. The GSM switching network 136 is coupled to the remainder of the GSM service network 140. The MSN 132 can communicate with both the RAN 112 and the GSM service network 140 by mapping messages in the desired format and structure in one cellular communication system to the desired format and structure in the second cellular communication system. For example, if one communication system is the GSM system and the second communication system is the CDMA2000-1x system, the hybrid MSN 132 will map the message from the format and structure known in the GSM system to the format and structure known in the CDMA1x system, and vice versa The same is true.

Figure 2 illustrates various interfaces in a network of multiple mobile switching nodes (MSN) and base stations (BS) 200. In Figure 2, multiple MSNs are connected to each other, and each of the MSNs has one or more associated base stations. MSN-A 204 is connected to BS-A.1 208 and BS-A.2 212 through a standard CDMA IOS-A interface 216. Similarly, the MSN-B 220 is connected to the BS-B 224 through the IOS A-interface 216. MSN-C 228 is also connected to BS-C.1 232 and BS-C.2 236 through the same IOS A-interface 216. Each MSN 204, 220 and 228 is connected to the GSM core network (SS7) 240 through the GSM MAP/E interface 244. The IOS message is encapsulated in the GSM A-interface BSSAP data and is transmitted through the GSM MAP/E interface 216. The BSSAP data will be composed of a BSSAP header and a DTAP or BSSMAP layer 3 message, and will be encapsulated in the GSM MAP/E interface in the BSS-APDU parameter.

FIG. 3A illustrates the DTAP data structure 300. The DTAP data structure is composed of multiple octets. The DTAP data structure is specifically composed of octet 1 (authentication 304), octet 2 (data link identification code (DLCI) 308), octet 3 (length identifier 312) and octet Section 4-N (application message 316) composition.

FIG. 3B illustrates the BSSMAP/BSMAP data structure 320. The BSSMAP/BSMAP data structure 320 is composed of octet 1 (authentication 324), octet 2 (length identifier 328), and octet 3-N (application message 332).

FIG. 3C illustrates the BSS-APDU data structure 336. The BSS-APDU data structure 336 is composed of octet 1 (element identifier 340), octet 2-3 (length 334), and octet 4-N (APDU 348). The length limitation of the APDU field 348 in the BSS-APDU data structure 336 is sufficient to encapsulate the ISOA-interface message. The IOS A-interface message will be encapsulated in the BSS-APDU data structure 336 and transmitted through the GSM MAP/E interface 244 in the same way as in the standard GSM system.

A single MSN may be connected to GSM1X and GSM RAN at the same time. Therefore, MSN will be needed to distinguish MAP/E interface messages from each radio access network (RAN). According to the GSM standard, the authentication mode (304, 324) is encoded in one octet. The least significant bit of this octet is called bit D, which indicates whether the message is a DTAP data structure 300 or a BSSMAP/BSMAP data structure 320. If the message is a DTAP data structure 300, the value of D is 1, and if the data structure is a BSSMAP/BSMAP data structure 320, the value of D is 0. The other bits of this octet will be used to separate message groups for different error interfaces. Before encapsulating the IOS A-interface message, MSN will set the most significant bit to "1". This bit will be ignored by the standard GSM RAN.

Figure 4 illustrates the signaling of a successful basic inter-MSN handover that requires a circuit connection between MSN-A and MSN-B. In this embodiment, the handover is initiated by BS-A. The handover request message 404 is sent to MSN-A. MSN-A sends a MAP-prep-handover request 408 to MSN-B, and the request includes a complete handover request message. MSN-B requests a switch number from its associated VLR (step 412). The switch number will be used to route the call connection from MSN-A to MSN-B. MSN-B then requests the allocation of radio resources (step 416). This will be done by sending the received handover request message to BS-B. When the radio resource is successfully allocated, the BS-B responds with a handover request validation message 420. The VLR returns the assigned handover number to MSN-B (step 424).

When MSN-B receives the handover number, it returns a MAP-ready-handover response 428 to MSN-A. The response includes the complete handover request confirmation message received from BS-B. MSN-A then sends an SS7 initial address message (IAM) 432 to start the circuit between MSN-A and MSN-B. When MSN-B receives a call from MSN-A using the switching number, it releases the switching number in the VLR by sending a MAP-send-switch-report response in step 436.

In step 440, MSN-B then signals that MSN-A has reserved the circuit for the call. When MSN-A receives the signal, it starts to switch the execution command (step 444). BS-A then sends a handover started message 448 to MSN-A. BS-B sends a handover complete message 452 to MSN-B, notifying that the mobile station is successfully communicating with BS-B. MSN-B then sends a MAP-send-end-signal request 456 to MSN-A, and the request includes a complete handover complete message. MSN-A sends a clear command message 460 to BS-A to release wireless resources. BS-A sends a clear complete message 464 to MSN-A to notify that all resources have been cleared.

When MSN-B receives the handover complete message from BS-B, it generates an SS7 response signal 468 directed to MSN-A. When the call is terminated (mobile station or fixed user), MSN-A clears the circuit between MSN-A and MSN-B in step 472. MSN-A then sends a MAP-send-end-signal response 476 to MSN-B to release the MAP resources in MSN-B.

Figure 5 illustrates the basic switching technique without the use of a circuit connection 500. In this embodiment, the handover is initiated by BS-A. The handover request message 504 is sent to MSN-A. MSN-A sends a MAP-ready-handover request 508 to MSN-B, and the sent request contains a complete handover request message. MSN-B requests the allocation of wireless resources by sending the received handover request message 512 to BS-B. When the unlimited resources are successfully allocated, the BS-B responds with a handover request confirmation message 516. When MSN-B receives the handover request confirmation message 516, it returns a MAP-ready-handover response 520 to MSN-A. The response includes the complete handover request confirmation message 516 received from BS-B. MSN-A then begins to switch to execute the command 524.

BS-A then sends a handover started message 528 to MSN-A. BS-B sends a handover complete message 532 to MSN-B, notifying that the mobile station is successfully communicating with BS-B. MSN-B then sends a MAP-send-end-signal request 536 to MSN-A. The request includes a complete handover complete message. MSN-A sends a clear command message 540 to release wireless resources. BS-A then sends a clear complete message 544 to MSN-A, notifying that all resources have been cleared. MSN-A then sends a MAP-send-end-signal response 548 to MSN-B to release the MAP resources in MSN-B. Note that in the description of FIG. 5, the information transfer about the circuit establishment and the information about the handover number allocation are not necessary.

The handover procedure is usually triggered by the BS-A sending a handover request message to MSN-A on the IOS A-interface. This basic inter-MSN handover procedure instruction is executed and controlled by MSN-A. Sending a MAP-ready-handover request to MSN-B is triggered when MSN-A receives a handover request message. The cell identity of the cell provided in the handover request message is mapped to the target cell ID MAP parameter, and the handover request message is encapsulated in the MAP-parameter-handover request BSS-APDU MAP parameter. The call in the cell will be in the MSN -B area is processed.

Figure 6 illustrates the signaling 600 for a successful subsequent handover from MSN-B to MSN-A between MSNs that require a circuit connection between MSC-A and MSC-B. BS-B sends a handover request message 604 to MSN-B. In response to this, MSN-B sends a MAP-preparation-follow-up-handover request 608 to MSN-A, which indicates the new MSN number and contains a complete handover request message. Since MSN-A controls MSN calls, no call number is required for call routing. Therefore, MSN-A immediately starts radio resource allocation by sending the received handover request 612 to BS-A.

When the radio resources are successfully allocated, the BS-A responds with a handover request confirmation message 616. MSN-A then sends a MAP-preparation-following-handover response 620 to MSN-B. The response includes a complete handover request confirmation message. MSN-B then begins to switch command 624. In response to this, BS-B sends a handover started message 628 to MSN-B. BS-A then sends a handover complete message 632 to MSN-A, notifying the mobile station that it is successfully communicating with BS-A. MSN-A then sends a MAP-send-end-signal response 636 to MSN-B. When the MSN-B receives the MAP-send-end-signal response 636, it sends a clear command message 640 to the BS-B, so that the wireless resources will be released. MSN-A clears the circuit between MSN-A and MSN-B in step 644 after sending the MAP-send-end signal response 636. BS-B sends a clear complete message 648 to MSN-B, notifying that all resources have been cleared.

The difference between the subsequent switching procedure from MSN-B to MSN-A without circuit connection and the subsequent switching procedure from MSN-B to MSN-A requiring circuit connection is that no circuit release is required between MSN-A and MSN-B (644).

Figure 7 illustrates the signaling 700 for a successful subsequent handover from MSN-B to MSN-C that requires a circuit connection between MSN-A and MSN-C. The BS-B initiates the handover by sending a handover request message 702 to MSN-B. MSN-B sends a MAP-prep-follow-switching request 704 to MSN-A, indicating a new MSN number and including a complete handover request message. The new MSN number is the number of MSN-C. MSN-A then sends a MAP-prep-handover request 706 to MSN-C. The request includes a complete handover request message. MSN-C then requests a handover number from its associated VLR (step 708). The switch number will be used to route the call connection from MSN-C.

MSN-C then requests (step 710) to allocate radio resources by sending the received handover request message to BS-C. When the radio resource is successfully allocated, the BS-C responds with a handover request confirmation message 712. The VLR then returns (step 714) the assigned handover number to MSN-C. When MSN-C receives the handover number, it returns a MAP-ready-handover response 716 to MSN-A. The response includes the complete handover request confirmation message 712 received from BS-C.

MSN-A then sends an SS7 initial address message (IAM) 718 to start the circuit connection between MSN-A and MSN-C. When MSN-C uses the switching number to receive a call from MSN-A, it releases the switching number in the VLR by sending a MAP-send-switch-report response 720. MSN-C then signals (step 722) that MSN-A has reserved the circuit for the call. MSN-A then sends a MAP-preparation-follow-handover response 724 to MSN-B. The response includes a complete handover request confirmation message. MSN-B then begins to switch command 726. In response to this, BS-B sends a handover start message 728 to MSN-B. BS-C then sends a handover complete message 730 to MSN-C, notifying that the mobile station is successfully communicating with BS-C. MSN-C then sends a MAP-send-end-signal request 732 to MSN-A. The request includes a complete handover complete message.

When MSN-C receives the handover complete message 732 from BS-C, it generates SS7 response signal 734 and sends it to MSN-A. MSN-A then clears (step 736) the circuit between MSN-A and MSN-B. MSN-A then sends a MAP-send-end-signal response 738 to MSN-B, which releases the MAP resources in MSN-B. MSN-B then sends a clear command message 740 to BS-B to release wireless resources. In response to this, BS-B sends a clear complete message 742 to MSN-B, notifying that all resources have been cleared.

When the call is terminated by the mobile station or the fixed user, MSN-A clears (step 744) the circuit between MSN-A and MSN-C. MSN-A then sends a MAP-send-end-signal response 746 to MSN-B, and MSN-B then releases the MAP resources in MSN-C. MSN-C then sends a clear command message 748 to BS-C to release radio resources. BS-C then sends a clear complete message 750 to MSN-C, notifying that all resources have been cleared.

FIG. 8 illustrates a call flow chart of the subsequent handover procedure 800 from MSN-B to MSN-C without a circuit connection between MSN-A and MSN-C. The handover is initiated by BS-B by sending a handover request message 804 to MSN-B. MSN-B sends a MAP-Preparation-Follow-Handover Request 808 to MSN-A, which indicates the new MSN number and contains a complete handover request message. The new MSN number is the number of MSN-C. MSN-A then sends a MAP-prep-handover request 812 to MSN-C. The request includes a complete handover request message. MSN-C then requests (step 816) to allocate radio resources by sending the received handover request message to BS-C. When the radio resource is successfully allocated, the BS-C responds with a handover request confirmation message 820. When MSN-C receives the handover number, it returns a MAP-ready-handover response 824 to MSN-A. The response includes the complete handover request confirmation message received from BS-C.

MSN-A then sends a MAP-preparation-follow-handover response 828 to MSN-B, and the response includes a complete handover request confirmation message. MSN-B then initiates a handover command 832 to BS-B. In response to this, BS-B sends a handover started message 736 to MSN-B. BS-C then sends a handover complete message to MSN-C, and the message contains a complete handover complete message. MSN-C then sends a MAP-send-end-signal request 744 to MSN-A, including a complete handover complete message. MSN-A then sends a MAP-send-end-signal response 748 to MSN-B to release the MAP resources in MSN-B. MSN-B then sends a clear command message 752 to BS-B to release wireless resources. In response to this, BS-B sends a clear complete message 756 to MSN-B, notifying that all resources have been cleared. MSN-A then sends a MAP-send-end-signal response 760 to MSN-C to release the MAP resources in MSN-C. MSN-C then sends a clear command message 764 to BS-C to release wireless resources. In response to this, BS-C sends a clear complete message 768 to MSN-C, notifying that all resources have been cleared.

Describes the electrical connection, coupling, and connection of various devices or components. The connection or coupling can be direct or indirect. The connection between the first and second device may be a direct connection and may be an indirect connection. Indirect connections may include intervening elements that will process the signals processed by the first device and send them to the second device.

Those skilled in the art can understand that information and signals can be represented by any of a variety of different technologies and processes. For example, the data, instructions, commands, information, signals, bits, symbols, and chips that may be involved in the above description can be represented by voltage, current, electromagnetic waves, magnetic fields or their particles, light fields or their particles, or any combination thereof. .

Those skilled in the art can further understand that the various illustrative logic blocks, modules, circuits, and algorithm steps described in conjunction with the embodiments disclosed herein can be implemented by electronic hardware, computer software, or a combination of both. In order to clearly illustrate the interchangeability between hardware and software, various illustrative components, block diagrams, modules, circuits, and steps are generally described according to their functionality. Whether these functions are implemented as hardware or software depends on the constraints of specific applications on the overall system design. Skilled technicians may implement the functions in different ways for each specific application, but this implementation decision should not be interpreted as a departure from the scope of the present invention.

The implementation or execution of various illustrative logic blocks, modules, and algorithm steps described in conjunction with the embodiments described here can be used: general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field A programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination designed to perform the functions described herein. A general-purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. The processor can also be implemented by a combination of computing devices, such as a combination of a DSP and a microprocessor, multiple microprocessors, one or more microprocessors combined with a DSP core, or any other such configuration.

The steps of the method or algorithm described in combination with the embodiments disclosed herein may be directly included in the hardware, in the software module executed by the processor, or in both. The software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, removable disk, CD-ROM or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor such that the processor can read information from the storage medium or write information to the storage medium. Alternatively, the storage medium may be integrated with the processor. The processor and storage medium may reside in the ASIC. The ASIC may reside in the user terminal. Alternatively, the processor and storage medium may reside as discrete components in the user terminal.

The above description of the preferred embodiments is provided to enable those skilled in the art to make or use the present invention. Various modifications of these embodiments are obvious to those skilled in the art, and the general principles defined here can be applied to other embodiments without using creative ability. Therefore, the present invention is not limited to the embodiments shown here, but should conform to the broadest scope consistent with the principles and novel features disclosed herein.