TECHNICAL FIELD

The present invention is directed, in general, to communication systems and, more particularly, to a system and method for providing enhanced cell selection for a communications terminal in a packet based communication system.

BACKGROUND

As wireless communication systems such as cellular telephone, satellite, and microwave communication systems become widely deployed and continue to attract a growing number of users, there is a pressing need to accommodate a large and variable number of communication subsystems transmitting a growing volume of data with a fixed resource such as a fixed channel bandwidth accommodating a fixed data packet size. Traditional communication system designs employing a fixed resource (e.g., a fixed data rate for each user) have become challenged to provide high, but flexible, data transmission rates in view of the rapidly growing customer base. The third generation partnership project long term evolution ("3GPP LTE") is the name generally used to describe an ongoing effort across the industry to improve the universal mobile telecommunications system ("UMTS") for mobile communications. The improvements are being made to cope with continuing new requirements and the growing base of users. Goals of this broadly based project include improving communication efficiency, lowering costs, improving services, making use of new spectrum opportunities, and achieving better integration with other open standards and backwards compatibility with some existing infrastructure that is compliant with earlier standards. The project envisions a packet switched communications environment with support for such services as VoIP ("Voice over Internet Protocol") and Multimedia Broadcast/Multicast Services ("MBMS"). MBMS may support services where base stations transmit to multiple user equipment simultaneously, such as mobile television or radio broadcasts, for example. The 3GPP LTE project is not itself a standard-generating effort, but will result in new recommendations for standards for the UMTS.

The UTRAN includes multiple Radio Network Subsystems ("RNSs"), each of which contains at least one Radio Network Controller ("RNC"). However, it should be noted that the RNC may not be present in the actual implemented systems incorporating

Long Term Evolution ("LTE") of UTRAN ("E-UTRAN"). LTE may include a centralized or decentralized entity for control information. In UTRAN operation, each RNC may be connected to multiple Node Bs which are the UMTS counterparts to Global System for Mobile Communications ("GSM") base stations. In E-UTRAN systems, the e-Node B may be, or is, connected directly to the access gateway ("aGW," sometimes referred to as the services gateway "sGW"). Each Node B may be in radio contact with multiple UEs (generally, user equipment including mobile transceivers or cellphones, although other devices such as fixed cellular phones, mobile web browsers, laptops, PDAs, MP3 players, and gaming devices with transceivers may also be UEs) via the radio Uu interface.

The wireless communication systems as described herein are applicable to, for instance, 3GPP LTE compatible wireless communication systems and of interest is an aspect of LTE referred to as "evolved UMTS Terrestrial Radio Access Network," or E- UTRAN and also UTRAN communications systems. Although the discussion uses E- UTRAN as the primary example, the application is not limited to E-UTRAN, LTE or 3GPP systems. Other example wireless communications systems include WiMAX and WLAN. In general, E-UTRAN resources are assigned more or less temporarily by the network to one or more UEs by use of allocation tables, or more generally by use of a downlink resource assignment channel or physical downlink control channel ("PDCCH"). LTE is a packet-based system and, therefore, there may not be a dedicated connection reserved for communication between a UE and the network. Users are generally scheduled on a shared channel every transmission time interval ("TTI") by a Node B or an evolved Node B ("e-Node B"). A Node B or an e-Node B controls the communications between user equipment terminals in a cell served by the Node B or e-Node B. In general, one Node B or e-Node B serves each cell. A Node B may be referred to as a "base station." Resources needed for data transfer are assigned either as one time assignments or in a persistent/semi-static way. The LTE, also referred to as 3.9G, generally supports a large number of users per cell with quasi-instantaneous access to radio resources in the active state. It is a design requirement that at least 200 users per cell should be supported in the active state for spectrum allocations up to 5 megahertz ("MHz"), and at least 400 users for a higher spectrum allocation. In order to facilitate scheduling on the shared channel, the e-Node B transmits a resource allocation to a particular UE in a downlink-shared channel ("PDCCH") to the UE. The allocation information may be related to both uplink and downlink channels. The allocation information may include information about which resource blocks in the frequency domain are allocated to the scheduled user(s), the modulation and coding schemes to use, what the size of the transport block is, and the like.

The lowest level of communication in the UTRAN or e-UTRAN system, Level 1 , is implemented by the Physical Layer ("PHY") in the UE and in the Node B or e-Node B and the PHY performs the physical transport of the packets between them over the air interface using radio frequency signals. In order to ensure a transmitted packet was received, an automatic retransmit request ("ARQ") and a hybrid automatic retransmit request ("HARQ") approach is provided. Thus, whenever the UE receives packets through one of several downlink channels, including command channels and shared channels, the UE performs a communications error check on the received packets, typically a Cyclic Redundancy Check ("CRC"), and in a later subframe following the reception of the packets, transmits a response on the uplink to the e-Node B or base station. The response is either an Acknowledge ("ACK") or a Not Acknowledged ("NACK") message. If the response is a NACK, the e-Node B automatically retransmits the packets in a later subframe on the downlink ("DL"). In the same manner, any uplink ("UL") transmission from the UE to the e-Node B is responded to, at a specific subframe later in time, by a NACK/ ACK message on the DL channel to complete the HARQ. In this manner, the packet communications system remains robust with a low latency time and fast turnaround time. The types of UEs the UTRAN or e-UTRAN environments can accommodate are many. One type of UE service that is presently proposed to be supported in UTRAN and e-UTRAN systems is a UE that includes support for one or more closed subscriber groups ("CSG"). A closed subscriber group, for purposes of this application, is a group of one or more cells (Node B or e-Node B stations, or base stations) on which the access is restricted to a limited group of one or more users, and which is not generally available for "public" access on the network. This type of UE, when registering with Node B or e-Node B devices, can communicate with certain stations that are available only to a limited group of UE devices. A single UE may be a member of multiple CSGs. A single cell may support multiple CSGs. Examples include arranging a Node B or e-Node B in a residence, office, apartment building, or area so that only certain subscriber group UEs may register with and communicate with the e-Node B station (typically referred to as a "cell"). Home cell stations for residences may be referred to as HNBs or eHNBs. For purposes of this application, the term NB includes HNBs, the term eNB includes eHNBs, and either term contemplates other like arrangements whether in homes, hotels, office parks, hospitals, universities, etc., including so-called femtocells.

In implementing a CSG scheme as proposed in the prior art, the UE typically accesses a cell by scanning frequencies or multiple radio access technology (RAT) parameters to locate cells in the CSG list. This scanning or searching step may take a significant amount of time and UE resources, also decreasing battery life for battery powered devices. Hence, the selection and/or camping on cells that are not part of the UE whitelist should be avoided as much as possible.

In the prior art solutions, the presently proposed CSG "whitelist" stores a unique CSG identifier ID that is uniquely associated with a cell. The UE, on power up or otherwise when switching cells due to traversing the cell boundary physically, or in response to other triggering events that require cell selection or cell reselection, needs to locate and access a cell. Presently, the UE will need to search for the cell from a range of possible frequencies and RAT parameters, including for example the encoding and modulation schemes needed to access the cell, and once the cell is identified and received, determine if there is a CSG ID match from a transmitted message. The prior art cell selection procedure takes substantial time for searching and requires the UE to expend power, a limited resource for portable battery powered devices. For example, in the present approaches the UE may encounter other CSG cells within the same RAT that do not transmit any of the CSG IDs present in the UE CSG whitelist. However, in the prior art solutions, the UE can only obtain the information after attempting to camp and receive the message with these cells CSG ID. The time spent incorrectly camping on CSG cells that are not part of the UE CSG whitelist, and the UE attempting to obtain the CSG ID from a transmitted message increases with the number of deployed CSG cells. Some proposed prior art solutions involve having the NB or eNB transmit additional information as a beacon or signal. However, these known approaches have several problems. These prior art solutions place additional demands and modifications on the standards and the software and hardware for the NBs in the system.

A need thus exists for methods and apparatuses to provide for rapid and efficient UE cell selection. For example, the UE should be able to efficiently identify and access cells without the need for additional signaling or modifications to or from the base stations. The need is for methods that, for example, enable a UE to efficiently identify and access a cell while having minimum impact on the efficiency and operation of the remaining services in the environment, the other UEs, the Node B or e-Node B devices, and the network.

SUMMARY OF THE INVENTION

An apparatus and method according to embodiments of the present invention provide enhanced cell identification and access for UEs.

In certain illustrative exemplary embodiments described below, the UE searches for cells and in the examples, the cells provide CSG functions. However, the approach of embodiments of the invention of storing additional cell information to provide rapid identification and access to a previously successfully accessed cell is not so limited. In addition to CSG IDs, other methods for identifying cells and storing cell information are also contemplated as part of the embodiments and these alternatives also fall within the scope of any appended claims.

According to an illustrative embodiment, a communication terminal such as a UE (typically a mobile phone or cell phone) is provided. In some embodiments, the UE may further implement a CSG function. The communication terminal may also include automatic and manual cell selection using a CSG list (the "CSG whitelist"). In one exemplary embodiment, the UE or communication terminal may temporarily associate a list of recently used cells with entries in a CSG whitelist. The stored information for these cells will include the CSG ID as in prior approaches and in addition for embodiments of the present invention, the stored information maintained within the UE will also include the RAT parameters, such as frequency, encoding, etc. and the physical cell identity information for previously successfully used cells. For UTRAN CSG cells, the physical cell identity is equivalent to the primary scrambling code (PSC) used in the cell. This additional information is stored so that the UE can rapidly access a previously used cell, without the need to search frequencies/RAT parameters to locate the cell.

According to another illustrative embodiment, a communication terminal may begin building a CSG whitelist using stored or acquired information. As an alternative, the UE may build a list of cells using other methods for identifying cells; the approach is not limited to CSGs, which are but one example. When the UE is first accessing a particular cell, the prior art approach may be used by scanning multiple frequencies or RATs to identify a cell to which the UE is granted access. This may be referred to as "camping" or "being camped on" a cell. After once successfully camping on a cell, the UE stores all of the parameter information required to again access the cell, possibly including for example the RAT parameters, physical cell information and frequency of the cell. In future cell searches, the UE may save time and resources by attempting to access these cells first using all of the stored information, so that cell acquisition times for the UE can be minimized and power can be saved. More accurate searching is achieved. Searching for cells with physical parameters which do not match the stored physical parameters is not needed. In an exemplary embodiment, the UE associates the stored physical parameters with a stored cell whitelist. In an alternative exemplary embodiment, the whitelist contains CSG IDs for cells. In one exemplary method of the invention, the stored RAT parameters for the cell are stored in a manner such that they are associated with the CSG ID in the CSG whitelist. For example, the CSG ID may be used as a look up table address or index pointer for cell information storage. In another embodiment, the storage for the CSG whitelist may be increased to include additional fields so that when the whitelist is accessed, the RAT parameters and other physical cell information are also provided. Compression techniques may be optionally used to provide additional embodiments of the invention where the UE stores the RAT parameters, PCI, cell frequency, etc., in a data compressed form associated with the CSG ID.

In one exemplary implementation, the additional stored information may be stored in embedded memory that is on board an integrated circuit that includes other UE functions. In another exemplary implementation, the additional information could be stored in a commodity integrated circuit for storing, such as without limitation a subscriber identity mode (SIM) card, or a FLASH device. EEPROM, SRAM, volatile and nonvolatile memory could be used to store the information. Compression techniques could be used to reduce the size of the stored information. Error detection, error correction and parity information may be stored with the information to increase reliability.

In one exemplary method embodiment, a UE having the additional stored information will first attempt to access a cell that has previously been accessed using the specific RAT parameters and stored PCI information. In some embodiments, this information may be stored along with the CSG ID. If, after a predetermined time or a predetermined number of attempts, the cell cannot be accessed, the additional stored information will be discarded and a search for the cell using the prior art approaches will be performed. In some exemplary embodiments, this search is performed using only the CSG ID. If this full search is successful, the UE may again store the RAT parameters, physical cell ID and any additional information that might make future accesses to the cell efficient. In this manner, the use of the invention presents advantages when successful, yet the embodiments of the invention remain compatible with the prior art approaches and changes to the RAT parameters and physical cell information of a particular cell will not prevent the UE from accessing it.

In another exemplary embodiment, the UE could store a single set of physical parameters, RATs, frequencies, etc., that correspond to one CSG ID. In other exemplary embodiments, a CSG may include several cells so that several sets of physical parameters, RATs, frequencies, etc. may be stored that correspond to a single CSG.

In another exemplary embodiment, the UE may store physical parameters that correspond to a cell that is not part of a whitelist. For example, access may be permitted by some cells to UEs that do not belong to a CSG for that cell, albeit at higher costs or lower priority than cells that do have the CSG ID on their whitelist. The UE may camp on and have access to these cells without the cell identification information on the whitelist.

The method embodiments of the present invention may be added to an existing UE architecture by implementing the methods in software. Alternative embodiments would be to implement the storage of the parameters for successfully accessed cells in hardware. For example, a CSG handler may be included in the UE and may store information to non- volatile memory to implement storing the physical access parameters for cells. In some embodiments, this additional information may be stored on the CSG whitelist. In other embodiments, it may be stored with cell information other than CSG IDs.

In another embodiment, when performing cell search at power up or at other times, the UE may be made to automatically search for cells that have complete parameters stored from a previous successful "camping" by the UE. In some exemplary embodiments, this search may include a CSG ID. By searching for these fully identified cells first, time for accessing a cell is minimized and thus power for the battery powered UE may be conserved, and cell selection may be performed faster. This efficient cell access search is a limited search, the UE may restrict this search to only the frequency, and RATs, that are stored for the cell of interest, and the UE may ignore most of the results on a given frequency without further consideration, as these are uninteresting (physical cell IDs don't match, as one example). In yet another embodiment, a computer readable medium stores instructions which, when executed by a programmable user equipment device, perform the methods of storing additional parametric information that is used to access a cell that has previously been accessed. The user equipment will attempt using the specific RAT parameters and stored PCI information along with the CSG ID to rapidly access the cell. If, after a predetermined time or a predetermined number of attempts, the cell cannot be accessed, the additional stored information may be discarded and a search for the cell using the prior art approaches may be performed using the CSG ID. If this full search is successful, the programmable UE may execute instructions stored on the computer readable medium that causes it to again store the RAT parameters, physical cell ID and any additional information that might make future accesses to the cell efficient. In this manner, the use of the computer readable medium embodiment of the invention presents advantages when successful, yet the embodiment of the invention remains compatible with the prior art approaches and changes to the RAT parameters and physical cell information of a particular cell will not prevent the UE from accessing it.

Use of exemplary embodiments of the invention does not require modification to the communications standards or the implementation of the NB or eNB devices. Thus, implementing the methods of the present invention has minimal impact on the system and architectures already determined. Use of UEs in the same environment that does not implement the invention is also robust; the UEs implementing the invention can operate alongside other UEs without impact on the operation of either type of device.

The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures or processes for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawing, in which: Figure 1 illustrates user equipment communicating to an e-Node B over an air interface, and an e-UTRAN communications system according to an exemplary embodiment of the present invention;

Figure 2 illustrates a block diagram of a communication terminal according to an exemplary embodiment of the present invention;

Figure 3 illustrates communication layers of a UE, eNB and MME according to an exemplary embodiment of the present invention;

Figure 4 illustrates a UE including a receiver for common subscriber group ("CSG") information, CSG storage, and CSG memory portions, an antenna and an e-Node B/Node B that may be used to implement an exemplary embodiment of the present invention;

Figure 5 illustrates additional details on the CSG memory and storage of the UE of Figure 5 that may be used to implement an exemplary embodiment of the present invention; Figure 6 illustrates a first portion of a state diagram that the UE of Figures 4 and 5 may use to implement exemplary embodiments of the present invention; and

Figure 7 illustrates a second portion of a state diagram that the UE of Figures 4 and 5 may use to implement exemplary embodiments of the present invention.

DETAILED DESCRIPTION Referring initially to Figure 1 , a system level diagram of a communication system including a wireless communication system is depicted. Figure 1 provides an example of an environment where the application of the principles of the present invention may be used. The wireless communication system provides, as a non-limiting example, an e- UTRAN architecture including base stations 13 providing e-UTRAN user plane (packet data convergence protocol/radio link control/media access control/physical transport) and control plane (radio resource control) protocol terminations directed towards user equipment 15 . Alternatively, for another non-limiting example, a UTRAN architecture could be used, however for the illustrative purposes of explaining the operations and use of the embodiments, the e-UTRAN architecture is described here. The base stations 13 are again shown interconnected with an X2 interface or communication link. The base stations 13 are also connected by an Sl interface or communication link to an evolved packet core ("EPC") including, for instance, MME/UPE 11 which may form an access gateway ("aGW," a system architecture evolution gateway). The Sl interface supports a multiple entity relationship between the mobility management entities/user plane entities and the base stations and supports a functional split between the mobility management entities and the user plane entities.

The base stations 13 may host functions such as radio resource management (e.g., internet protocol ("IP"), header compression and encryption of user data streams, ciphering of user data streams, radio bearer control, radio admission control, connection mobility control, and dynamic allocation of resources to user equipment in both the uplink and the downlink). Additional functions may include selection of a mobility management entity at the user equipment attachment, routing of user plane data towards the user plane entity, scheduling and transmission of paging messages (originated from the mobility management entity), scheduling and transmission of broadcast information (originated from the mobility management entity or operations and maintenance), and measurement and reporting configuration for mobility and scheduling. The mobility management entity /user plane entity MME/UPE 11 may host functions such as distribution of paging messages to the base stations, security control, terminating user plane ("U-plane") packets for paging reasons, switching of U-plane for support of the user equipment mobility, idle state mobility control, and system architecture evolution bearer control. The user equipment 15 receives an allocation of a group of information blocks from the base stations.

Figure 2 illustrates a simplified system level diagram of an example communication element of a communication system. Figure 2 provides an illustration of an environment and structure for application of the principles of the present invention. The communication element may represent, without limitation, an apparatus including a base station, user equipment, such as a terminal or mobile station, a network control element, or the like. The communication element 31 includes, at least, a processor 32, memory 34 that stores programs and data of a temporary or more permanent nature, an antenna 38, and a radio frequency transceiver 36 coupled to the antenna and the processor for bidirectional wireless communication. Other functions may also be provided. The communication element 31 may provide point-to-point and/or point-to -multipoint communication services.

The communication element 31 , such as a base station in a cellular network, may be coupled to a communication network element 33, such as a network control element of a public switched telecommunication network. The network control element may, in turn, be formed with a processor, memory, and other electronic elements (not shown). The network control element 33 generally provides access to a telecommunication network such as a public switched telecommunication network ("PSTN"). Access may be provided using fiber optic, coaxial, twisted pair, microwave communication, or similar communication links coupled to an appropriate link-terminating element. A communication element 31 formed as a mobile station is generally a self-contained device intended to be carried by an end user; however, in areas where wired services are not available, the mobile station may be permanently installed at a fixed location as well. The processor in the communication element 31 , which may be implemented with one or a plurality of processing devices, performs functions associated with its operation including, without limitation, encoding and decoding of individual bits forming a communication message, formatting of information, and overall control of the communication element, including processes related to management of resources. Exemplary functions related to management of resources include, without limitation, hardware installation, traffic management, performance data analysis, tracking of end users and mobile stations, configuration management, end user administration, management of the mobile station, management of tariffs, subscriptions, and billing, and the like. The execution of all or portions of particular functions or processes related to management of resources may be performed in equipment separate from and/or coupled to the communication element, with the results of such functions or processes communicated for execution to the communication element. The processor of the communication element 31 may be of any type suitable to the local application environment, and may include one or more of general-purpose computers, special-purpose computers, microprocessors, digital signal processors ("DSPs"), and processors based on a multi-core processor architecture, as non-limiting examples.

The transceiver of the communication element 31 modulates information onto a carrier waveform for transmission by the communication element via the antenna to another communication element. The transceiver demodulates information received via the antenna for further processing by other communication elements.

The memory of the communication element 31 , as introduced above, may be of any type suitable to the local application environment, and may be implemented using any suitable volatile or non-volatile data storage technology, such as a semiconductor-based memory device, a magnetic memory device and system, an optical memory device and system, fixed memory, and removable memory. The programs stored in the memory may include program instructions that, when executed by an associated processor, enable the communication element to perform tasks as described herein. Exemplary embodiments of the system, subsystems, and modules as described herein may be implemented, at least in part, by computer software executable by processors of, for instance, the mobile station and the base station, or by hardware, or by combinations thereof. Other programming may be used such as firmware and/or state machines. As will become more apparent, systems, subsystems and modules may be embodied in the communication element as illustrated and described above.

Figure 3 depicts an illustrative and non-limiting example block diagram of an embodiment of user equipment 15 and a base station 13 constructed according to the principles of the present invention. Other protocols and layers could also be used with embodiments of the present invention. The user equipment UE 15 and the base station eNB 13 each include a variety of layers and subsystems: the physical layer ("PHY") subsystem, a medium access control layer ("MAC") subsystem, a radio link control layer ("RLC") subsystem, a packet data convergence protocol layer ("PDCP") subsystem, and a radio resource control layer ("RRC") subsystem. Additionally, the user equipment and the mobile management entity 11 include a non-access stratum ("NAS") subsystem. The example physical layer subsystem shown supports the physical transport of packets over the air interface and provides, as non-limiting examples, cyclic redundancy check ("CRC") insertion (e.g., a 24 bit CRC is a baseline for physical downlink shared channel ("PDSCH"), channel coding, physical layer hybrid-automatic repeat or retransmit request ("HARQ") processing, and channel interleaving). The physical layer subsystem also performs scrambling such as transport-channel specific scrambling on a downlink- shared channel ("DL-SCH"), broadcast channel ("BCH") and paging channel ("PCH"), as well as common multicast channel ("MCH") scrambling for all cells involved in a specific multimedia broadcast multicast service single frequency network ("MBSFN") transmission. The physical layer subsystem also performs signal modulation such as quadrature phase shift keying ("QPSK"), 16 quadrature amplitude modulation ("QAM") and 64 QAM, layer mapping and pre-coding, and mapping to assigned resources and antenna ports. The media access layer or MAC performs the HARQ functionality and other important functions between the logical transport layer, or Level 2, and the physical transport layer, or Level 1.

Each layer is implemented in the system and may be implemented in a variety of ways. More or fewer layers could be used, and in alternative layer protocols, layers could be combined. A layer such as the PHY in the UE 15 may be implemented using hardware, software, programmable hardware, firmware, or a combination of these as is known in the art. Programmable devices such as DSPs, reduced instruction set ("RISC"), complete instruction set ("CISC"), microprocessors, microcontrollers, and the like may be used to perform the functions of a layer. Reusable design cores or macros as are provided by vendors as ASIC library functions, for example, may be created to provide some or all of the functions and these may be qualified with various semiconductor foundry providers to make design of new UEs, or e-Node B implementations, faster and easier to perform in the design and commercial production of new devices.

Figure 4 depicts an illustrative embodiment. In Figure 4, a cellular base station eNB/NB 53 transmits cell information such as CSG information to UE 55 over the air interface using radio frequency signals via an antenna 51. In some applications, certain CSG information such as CSG identity may be transmitted to the UE over the air interface. The CSG information is then forwarded within the UE from a receiver area to CSG storage, which comprises in this exemplary embodiment either local memory 57, including volatile or non-volatile memory, or a removable media storage such as flash cards, smart cards, compact flash and the like, or permanent or semi-permanent storage 59 provided by the cellular provider to the UE, such as a subscriber identity module ("SIM") card, which is a non-volatile storage card. SIM cards such as 59 may be provided by the service provider when the UE is initially activated, when additional features are added, or at other times. The SIM card 59 may be moved to another UE so that the user may maintain the list of subscriber features including a user phone number, frequently called phone numbers, subscriber data features, and CSG whitelist information that are part of the services the user purchases from the service provider, and thus the user may import that SIM card into another UE to access the services without changing phone numbers or losing the subscriber information.

The CSG information includes a list of cells that the UE is a subscriber to or member of, referred to as the "CSG whitelist." In this exemplary embodiment, the network may provide the CSG whitelist to the UE in accordance with the subscriber information stored in the MME or other network resource. The CSG whitelist is used by the communications system to determine which cells, or base stations (e-Node B stations or "eNB" in e-UTRAN standard terminology), the UE can register with. As the UE is used in different environments, the "whitelist" may expand to include generally open cells such as eNB equipments located in hotels, cafes, office parks and the like. Home NBs and Home eNBs may be accessed. Femtocells or other cells may be accessed. The UE may gain access to these automatically, or the user may have to enter these into a list using a user interface, for example, a business may grant customers the option to become subscribers to their cell and an access code or other password may be required. As the UE is used in different environments, the UE CSG storage handler that manages the CSG whitelist may add cells to which the UE gained access in the past, that is, the cells on which the UE has previously "camped."

In embodiments of the present invention, the UE may store, for cells that were previously successfully accessed, additional parametric information. The stored parametric information may include RAT parameters such as the type of RAT, which may be for example UTRAN or e-UTRAN, frequency, physical cell identification fields including the PSC. The stored information is associated with the cell specific information such as a unique CSG ID field. By using the stored information the next time the UE attempts to access the cell, efficient cell search may be performed and the need to search or scan multiple RAT parameters or frequencies to locate a cell may be eliminated, or minimized. Of course, if the UE has not previously camped on the cell, this information will not be available to it and before such information has been stored, a full searching step will be necessary. In some exemplary embodiments, this search may use CSG ID information, although other cell information could be used. Figure 5 depicts a detailed block diagram view of one example implementation of the CSG functionality provided within the UE 55. CSG storage handler 61 may be implemented as hardware, using ASIC or semicustom integrated circuitry, or using a programmable device such as a microprocessor, RISC core, or a state machine. CSG storage handler 61 resides within the UE and may be part of integrated circuitry incorporating other functions of the UE, or could be implemented along with non-volatile storage such as local memory 57 using integrated circuit technologies and semiconductor fabrication facilities available from wafer foundries, as is known in the art. SIM card 59 may also store part of the CSG whitelist. These entries are also considered more or less permanent and may include the CSG information relating to the user's home, office, university, or neighborhood, the cells where the UE is a permanent member of the subscriber group. Local memory 57 is depicted having two areas of storage, user permanent entries

60, and, user temporary entries 58. The whitelist will include cells or eNBs where the UE has "camped" and been granted access. In some exemplary embodiments the whitelist will be a list of CSG IDs, although other information identifying cell could be used. By maintaining the list of cells where the UE has previously successfully been used, the registration process for the UE on power up, or the re -registration process needed as the UE moves from one cell signal receiving area to another, may be made much quicker. This process is detailed below, but by providing the CSG whitelist, the cell selection and registration process may be made more efficient. Advantages of the use of the invention may include, for example, saving battery power and time. The temporary whitelist will be updated. The UE may be set to automatically update the whitelist. The UE may also conduct cell identification as a background task, updating the whitelist for future use even while camping on another cell. The cell identification may include, for example, CSG IDs or other identification information that identifies a cell.

Figure 6 depicts, in a state transition diagram, methods for operating a UE in accordance with exemplary embodiments of the present invention.

When a UE is powered "on" from an "off state, it must first determine what networks are available and which network to connect to. In addition, it must identify a suitable cell, if one is available, to register with ("camp" on). Once a UE is registered with a cell on a network or "camped", the UE is active and can be paged, for example, to receive calls or data, or can initiate a call or data transmission. At power up, the public land mobile network ("PLMN") is selected based on various criteria. In Figure 6, this is depicted as the entry point for state 01, "Cell Selection". In one embodiment, the UE can automatically select the network, or, in an alternative approach, the UE can prompt the user, listing available networks, and the user can select a network. The UE must monitor radio transmissions from cells to determine what networks are available for selection. In some exemplary embodiments, part of the beacon signals transmitted from the cells or eNBs includes the information identifying the CSGs the cell supports. Following the network or PLMN selection, the UE must select a cell. The added functionality of the CSG or the other cell identification used, and the enhanced parametric information stored along with the whitelist, will affect the cell selection process and is further described below. From the Cell Selection state 01 , the state diagram transition either to state 03, when the UE has stored information for one or more available cells in the CSG whitelist, or to state 06, when there is no entry in the CSG whitelist. State 06, the Initial Cell Selection state, will be used for UEs being powered up for the first time or when the whitelist has been cleared for some reason. If there is no stored information in the UE and no CSG whitelist, the UE transitions to a state 06 labeled "Initial Cell Selection" in Figure 6. In this state, the UE attempts to identify a suitable cell. A suitable cell for a UE without a CSG whitelist is one that is part of the PLMN and that fulfills other "suitable cell" criteria that are provided by the system.

In state 06, the Initial Cell Selection state, the UE has no stored information about a cell so a full search must be performed, using multiple RAT parameters, multiple frequencies and other parameters, to locate an available cell and to access it. Once this is done, the state transition diagram transitions to the "Camped Normally" state, state 02. Since the UE in this exemplary situation has no CSG information already stored, it may store the CSG ID (or other cell identification information, as an alternative) on its local memory CSG whitelist. Further, in accordance with embodiments of the present invention, the UE may store the RAT parameters, frequency, and physical cell ID for the cell it has camped on, so that in future accesses it can efficiently select and access this cell without the need to do a full search for a cell.

If instead the UE does have entries on the CSG whitelist, the state diagram transitions to state 03, the Stored Information Cell Selection state. From this state, certain method embodiments of the invention are shown in detail on Figure 7 for selecting a cell using, for example, the CSG ID to index stored parameters for the cell. These steps are described in detail below. After a suitable cell is located, the state diagram of Figure 6 again transitions to the "Camped Normally" state, 02. Again, the UE may store the parametric information associated with the cell (if it has not previously done so, or needs to update the stored information for the cell), so that in the future, it may efficiently access this cell again. The dashed circle leaving state 02, "Camped Normally", denotes another path to the steps of Figure 7; the UE may in a background mode continue to identify cells, and store the physical information needed to access the cells, continuously updating the whitelist. This process also improves the efficiency of future accesses.

Periodically, an event may cause the UE state to transition out of the "Camped Normally" state into the Cell Reselection state, 05. In some examples, the UE may be traveling out of range of the selected cell, signal strength or loading may change, or some other event may cause the UE to reselect (the user or network could remove the cell from the CSG whitelist for example). The reasons for entering the "Cell Reselection " state are referred to here collectively as "triggers" and may include time elapses, location changes, reception changes, changes by a user command, changes by a system command, and other factors.

In any event, on the detection of a "Trigger", the UE will transition to the "Cell Reselection" state and again attempts to find a suitable cell. From the Cell Reselection state, the state diagram transitions to the cell selection states shown on Figure 7 for using the method embodiments of the present invention, and then if a suitable cell is located, transitions to state 02 again. When entering the "Camped Normally" state, the UE may store the parametric information associated with the cell, if it has not previously done so. In an exemplary method, cells on the CSG whitelist will be searched for first using the additional stored information of the embodiments.

In some embodiments, the UE may start with the most recently accessed CSG ID cells. In alternative embodiments, the UE may start with the permanent CSG whitelist where the UE has additional information, then proceed to the CSG whitelist for cells where the UE does not have additional parameters stored for efficient access.

In a case where the UE is in the "Camped Normally" state and a message is received that requires action by the UE, for a simple non-limiting example, a paging message, the state diagram may transition to the "Connected Mode" 07 and then back to the "Camped Normally" state. Once a suitable cell is located, the UE transitions to the "Camped Normally" state, state 02 in Figure 6. Registration with the network is then performed. A registered UE is available for paging, can receive information and parameters, and can initiate a transition to a "Connected Mode" state in Figure 6 to communicate with the network.

Whenever the UE state is in state 02, "Camped Normally", the UE may identify a cell that has information stored on the whitelist. Alternatively, the UE may, in a background mode, identify a cell that is available for access but which is not stored on a whitelist. In some embodiments, the UE may receive CSG ID information, or a cell may indicate it is "open" for all UEs to access. The UE may proceed as a background task to identify the physical parameters associated with the cell and update the whitelist, even while camped on another cell.

In the embodiments of the present invention, whenever the UE goes through a cell selection process and successfully camps on a cell where the stored information for that CSG ID does not include the various RAT and frequency parameters, the UE will then create a new set of stored parameter information associated with that CSG ID. Then, on the next attempt to access that cell, for example by using the CSG ID, the UE will first attempt rapidly connecting to the cell using the stored physical parameters.

In some cases, the UE may not be able to find a suitable cell. In that case, the state diagram transitions back to state 01 and the selection process begins again. In some embodiments, a different PLMN selection may be made when repeated attempts to locate an available cell are unsuccessful.

Figure 7 depicts a simplified state diagram illustrating the states and the decision branches used in one exemplary embodiment of the cell selection method. In Figure 7, state 16 depicts an entry from one of the cell selection states 03 or 05 depicted in Figure 6.

In state 08, the state diagram shows a decision state. If the UE has stored additional parameters for the CSG ID, meaning the UE has previously successfully "camped" on that cell, a transition is made to state 12, "Attempt efficient cell access without full searching". If there is no additional stored parametric information, the transition is to state 09, where a full search for the cell is performed using the multiple RAT parameters and multiple frequency searching. In this example, a UE that transitions to state 09 is performing method steps similar to the Initial Cell Selection in Figure 6.

In the embodiments of the present invention, the UE typically has additional parametric cell information stored in local memory for cells that have previously been successfully "camped" on. In that case, the efficient cell access search without full searching step is performed in state 12. This additional stored information makes it possible for the UE to immediately attempt to access the cell using the RATs, frequency and physical cell ID that were successfully used earlier, to quickly confirm whether the cell identified by the CSG ID can still be accessed without performing the lengthy cell searches of the prior art.

In state 14, another decision state is shown. If the stored CSG ID indexed parametric information related to the RATs, the frequency and so forth fail to provide a good connection to the cell, the UE will then process that information and after a certain number of attempts, or alternatively after a predetermined time period, stops trying to access the cell in this manner.

The UE will then transition to state 09, and revert to the frequency and RAT searching used in the prior art cell selection processes. This could happen for several reasons. The cell stored parametric information may be out of date; for example, if a home NB is powered down and then reinitialized, some of the RAT parameters, frequency, etc., may be reassigned by the network and the UE will not be able to quickly access it using the previously stored information.

In some embodiments of the invention, the stored parametric information may automatically be discarded from the local memory on the UE when an attempt to use it fails to locate the cell. If the UE then later subsequently successfully locates the cell and again camps on the cell, the UE stores new RAT parameters, frequency information, etc., associated with the unique CSG ID for the cell; so that for the next attempt to access that same cell, the stored parametric information has been updated. The states of Figures 6 and 7 are example embodiment state diagrams for implementing the cell selection and reselection process for a UE including support for the rapid cell selection using CSG and CSG whitelist functions of the various embodiments of the present invention. As is known to those skilled in the art, these states and the transitions between them may be combined or rearranged and these alternative implementations are also contemplated as exemplary embodiments that fall within the scope of the invention and are covered by the appended claims.

In additional illustrative embodiments, the efficient cell access without searching may be performed on a periodic basis. The advantage of the embodiments of the invention is that the stored physical parametric information available to the UE may make this limited search much more efficient than the full cell searches of the prior art. The UE can restrict this efficient cell access search to the stored frequency and RAT and the UE can ignore uninteresting responses on the frequency used, so that only the received message with the correct physical cell ID field is needed. The remaining search results can be ignored without further consideration.

In additional illustrative embodiments, the cell search and selection process may be controlled by the user using the stored CSG whitelist. The UE may be configured to automatically, or manually, perform a limited cell search and cell selection process. Embodiments of the present invention provide solutions to a rapid cell selection CSG function in UEs in the environment. The use of additional information stored and associated with the cells in the CSG whitelist may enable the system to implement an enhanced UE with rapid cell selection without modifying the communications standards, or requiring modifications to the Node B or e-Node B hardware or software. Embodiments of the present invention may be implemented in software in an existing UE architecture, and UEs with the rapid cell selection features of the present invention can interoperate with UEs that do not have the feature, so there is no need to modify existing UEs. The embodiments of the present invention as presented herein may provide advantages in efficient cell selection. The embodiments also advantageously remain compatible with the existing services and interoperable with UEs and networks determined previously. Embodiments of the present invention also have advantages in providing UE devices including an efficient cell selection using enhanced CSG functionality at a reduced or minimum cost and with as little wasted system bandwidth. In one embodiment, an apparatus comprises a communications terminal comprising a cell identification storage handler, cell identification storage for storing physical parameters such as RAT and frequency and physical cell identification associated with a cell identification, wherein the storage handler retrieves the stored physical parameters and the communications terminal performs efficient cell searching utilizing the retrieved physical parameters,

In another embodiment, an apparatus comprises a communications terminal comprising a cell identification storage handler, cell identification storage for storing physical parameters such as RAT and frequency and physical cell identification associated with a cell identification, wherein the storage handler stores physical parameters associated with cell identification when the communications terminal establishes an access with the cell.

In another embodiment, an apparatus comprises user equipment comprising a processor, data memory, storage for a CSG whitelist, a CSG ID storage handler adapted to store and retrieve CSG IDs from the CSG whitelist, additional storage for storing physical parameters such as RAT and frequency and physical cell identification associated with a CSG ID, wherein the storage handler retrieves the stored physical parameters and the processor performs efficient cell searching utilizing the retrieved physical parameters and the CSG ID. In another embodiment, the apparatus above is provided wherein the storage is non-volatile. In yet another embodiment, the apparatus provided above wherein the storage comprises a SIM card. In yet another embodiment, the apparatus described above is provided wherein the storage comprises embedded memory. In yet another embodiment, the apparatus described above wherein the processor, CSG storage handler and the storage are integrated onto an integrated circuit. In yet another embodiment, the above described integrated circuit apparatus wherein the storage comprises embedded FLASH memory on the integrated circuit.

In a method embodiment, a method comprising storing cell identification information on a whitelist, storing additional physical parameters associated with the stored cell identification information, retrieving stored physical parameters, performing a cell search using the retrieved stored physical parameters, and accessing a cell using the retrieved stored physical parameters.

In an alternative method embodiment, a method comprising storing CSG IDs for cells on a CSG whitelist, receiving physical parameters for cells indexed by the CSG IDs, storing physical parameters of a cell after a successful cell access, retrieving physical parameters for a cell indexed by a CSG ID, and searching for a cell using the retrieved physical parameters. In an alternative embodiment, the above described method and further comprising stopping the search for the cell after a predetermined number of attempts, searching for the cell using the CSG ID over variety of frequencies and RATs, identifying the cell, accessing the cell, and storing updated physical parameters for the cell indexed by the CSG ID.

In another embodiment, an apparatus comprises user equipment comprising means for storing CSG IDs, means for storing physical parameters such as RAT and frequency and physical cell identification associated with a CSG ID, storage handler means for retrieving the stored physical parameters, means for performing efficient cell searching utilizing the retrieved physical parameters and the CSG ID. In yet another embodiment, the apparatus above further comprises a means for transceiving for communicating over an air interface. In another embodiment, a computer readable medium comprises instructions that, when executed by a programmable user equipment device, perform the method of storing CSG IDs for cells on a CSG whitelist, receiving physical parameters for cells indexed by the CSG IDs, storing physical parameters of a cell after a successful cell access, retrieving physical parameters for a cell indexed by a CSG ID, and searching for a cell using the retrieved physical parameters. In an alternative embodiment, the computer readable medium above described further comprises instructions that, when executed by the programmable user equipment device, comprise stopping the search for the cell after a predetermined number of attempts, searching for the cell using the CSG ID over variety of frequencies and RATs, identifying the cell, accessing the cell, and storing updated physical parameters for the cell indexed by the CSG ID.

In certain illustrative exemplary embodiments described herein, the UE searches for cells and in the examples, the cells provide CSG functions. However, the approach of embodiments of the invention of storing additional physical cell information to provide efficient cell identification and access to a previously successfully accessed cell is not so limited; in addition to CSG IDs, other methods for identifying cells and for storing cell information are also contemplated as part of the embodiments of the invention and these alternatives also fall within the scope of any appended claims.