HK1099168A - Parallel cell id acquisition in frequency division multiple access systems - Google Patents

Abstract

This disclosure is directed to cell acquisition techniques for telecommunication systems that implement FDMA and TDMA techniques, such as GSM systems. The techniques make efficient use of processing time in order to accelerate the cell acquisition process. Upon acquiring synchronization information of a first cell of an FDMA system, the timing for the acquisition of cell identification (ID) information associated with the first cell can be scheduled based on the synchronization information of the first cell. Synchronization information of a second cell of the FDMA system can then be acquired prior to acquiring the cell ID information associated with the first cell. Moreover, synchronization information of a additional cells may similarly be acquired prior to acquiring the cell ID information associated with the first cell. In this manner, efficient use of processing time can be achieved between the acquisition of synchronization information and the acquisition of cell ID information.

Description

Parallel cell identity acquisition in a frequency division multiple access system

Technical Field

The present invention relates to wireless communications, and more particularly, to cell selection in wireless communication systems implementing Frequency Division Multiple Access (FDMA) and Time Division Multiple Access (TDMA).

Background

A wide variety of wireless communication technologies have been developed to facilitate wireless telecommunications. In the present invention, the phrase Frequency Division Multiple Access (FDMA) refers broadly to any wireless communication technique that divides an allocated frequency spectrum into a plurality of smaller frequency cells. Each cell of the allocated spectrum has a carrier signal that can be modulated with data. Dividing the allocated spectrum into cells can increase the amount of data that can be transmitted over the spectrum and also provide a simple mechanism for service providers to allocate bandwidth proportionally. For example, a particular cell may be assigned to a particular service provider, and a wireless network of a given service provider may use one or more cells to provide service to its users.

In the present invention, the phrase Time Division Multiple Access (TDMA) broadly refers to a wireless communication technique in which frequency cells are divided into time slots. In systems implementing TDMA techniques, different wireless communications are transmitted during specific time slots, and in some cases time slots may be allocated for communication based on a subscription. Thereby, a single frequency cell can support multiple time division communication channels.

The global system for mobile communications (GSM) standard, standardized by the European Telecommunications Standards Institute (ETSI), is an example of a system that utilizes FDMA and TDMA techniques. For example, in europe, frequency bands around 900 megahertz (MHz) and around 1800MHz have been allocated to GSM. The frequency band around 900MHz and around 1800MHz is divided by GSM into about 548 frequency cells, with each cell being about 200 kilohertz (KHz). Within each cell, TDMA techniques are performed, wherein time slots are used for time allocation communications. Different cells may be assigned to different service providers for use in the service provider's network. Some cells act as network beacons to inform subscriber units of which cells are associated with a given network, while other cells are used only to pass network traffic between subscriber units.

One challenge in systems using FDMA techniques, such as GSM, is the cell selection or acquisition process by a subscriber unit. A subscriber unit refers to devices used by end users such as a mobile radiotelephone and the like. In an FDMA system, the subscriber unit scans the various cells of the allocated spectrum and measures the power of the cells to find the most desirable cell for telecommunication. The most desirable cell is typically a cell associated with the subscriber unit's service provider's network or, possibly, a cell for which the subscriber unit's service provider has a good roaming agreement. For a given subscriber unit, when selecting cells, for example, in a given service provider's network, cells with higher power signals are also more desirable than lower power cells.

Disclosure of Invention

In one embodiment, the present disclosure sets forth a method comprising the steps of: acquiring synchronization information of a first cell of a Frequency Division Multiple Access (FDMA) system; schedule a time to acquire cell Identification (ID) information associated with the first cell based on synchronization information of the first cell; and acquiring synchronization information of a second cell of the FDMA system prior to acquiring cell ID information associated with the first cell.

In another embodiment, the invention features a subscriber unit of an FDMA system, the subscriber unit comprising: a receiver that receives a first signal associated with a first cell of the FDMA system and a second signal associated with a second cell of the FDMA system; and a control unit that acquires synchronization information of the first cell, schedules a time to acquire cell ID information associated with the first cell based on the synchronization information of the first cell, and acquires synchronization information of the second cell before acquiring the cell ID information associated with the first cell.

In yet another embodiment, the disclosure sets forth a computer-readable medium comprising instructions for: a subscriber unit of an FDMA system is caused to acquire synchronization information of a first cell of the FDMA system, schedule a time to acquire cell ID information associated with the first cell based on the synchronization information of the first cell, and acquire synchronization information of a second cell of the FDMA system prior to acquiring the cell ID information associated with the first cell.

In another embodiment, the invention features a subscriber unit of an FDMA system, the cell including: means for obtaining synchronization information for a first cell of the FDMA system; means for scheduling a time to acquire cell ID information associated with the first cell based on synchronization information of the first cell; and means for acquiring synchronization information of a second cell of the FDMA system prior to acquiring cell ID information associated with the first cell.

In another embodiment, the invention describes a method implemented in a global system for mobile communications (GSM). The method comprises the following steps: acquiring a Frequency Correction Channel (FCCH) and a Synchronization Channel (SCH) of a first cell; scheduling a time for decoding a broadcast channel (BCCH) associated with the first cell based on the SCH of the first cell; and acquiring the FCCH and SCH of a second cell prior to decoding the BCCH associated with the first cell.

The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.

Drawings

Figure 1 is a block diagram illustrating a wireless communication system implementing FDMA and TDMA communication techniques according to the teachings of this disclosure.

Fig. 2 is a flow chart illustrating a cell selection process implemented by a subscriber unit of a wireless communication system.

Fig. 3 is a more detailed block diagram of certain components of the subscriber unit illustrated in fig. 1 in accordance with the present invention.

Fig. 4 and 5 are flow diagrams illustrating processes implemented within a subscriber unit in accordance with the present invention.

Detailed Description

The present invention relates to cell acquisition techniques for use with telecommunication systems that implement FDMA and TDMA techniques, such as GSM systems. The technique can effectively utilize the processing time to accelerate the cell acquisition process. For example, upon acquiring synchronization information of a first cell of an FDMA system, a timing of acquiring cell Identification (ID) information associated with the first cell can be scheduled based on the synchronization information of the first cell. Synchronization information for a second cell of the FDMA system can then be acquired prior to acquiring cell ID information associated with the first cell.

In other words, rather than acquiring synchronization information for a cell and then waiting for the cell ID information, the techniques described herein may more efficiently utilize the processing time between acquiring synchronization information for a given cell and acquiring the cell ID information. Specifically, the techniques may utilize the time between acquisition of synchronization information for a first cell and acquisition of the cell ID information to acquire synchronization information for a second cell, and possibly a third cell, a fourth cell, a fifth cell, and so on.

Acquisition of cell ID information for each cell may then be performed according to a scheduling scheme that identifies when the cell ID information will be received. In GSM, the time between acquiring synchronization information for a given cell and acquiring the cell ID may take 1 second due to the repeatability of the messages needed to acquire the cell ID. On the other hand, the time taken to acquire the synchronization information is generally less than 50 to 100 milliseconds. Parallel acquisition of cell IDs can speed up the identification process of a desirable cell for subscriber unit registration and can more efficiently utilize processing time.

Fig. 1 is a block diagram illustrating a wireless communication system 10 implementing a Frequency Division Multiple Access (FDMA) communication technique and a Time Division Multiple Access (TDMA) technique. For example, system 10 may include a global system for mobile communications (GSM) compliant with the European Telecommunications Standards Institute (ETSI) GSM standard. The ETSI GSM standard employs an FDMA technique that divides a frequency band into a plurality of cells and a TDMA technique that uses time allocation for communication during specific time slots within the cells. In the following description, various techniques will be described in connection with GSM. However, the same or similar techniques may also be used with numerous other wireless protocols or standards that employ FDMA and TDMA.

The wireless communication system 10 includes a plurality of base stations 12A-12C (collectively base stations 12) that communicate with a subscriber unit 14. Although a single subscriber unit 14 is shown, the system 10 typically includes a plurality of such units. Subscriber unit 14 generally refers to a wireless device used by an end user. In a GSM system, for example, subscriber unit 14 typically comprises a mobile radiotelephone. However, subscriber unit 14 may also be implemented in any of a number of other portable computing devices, such as a desktop or portable computer, a Personal Digital Assistant (PDA), an interactive television, a wireless data terminal, a wireless data collection device, or any other wireless device configured to communicate in accordance with the techniques described in this disclosure.

Base station 12 is typically a fixed device that communicates wirelessly with subscriber unit 14 to provide network access to subscriber unit 14. For example, the base station 12 may provide an interface between the subscriber unit 14 and a Public Switched Telephone Network (PSTN) to route telephone calls to and from the subscriber unit 14. Alternatively or additionally, base station 12 may be coupled to a packet-based network for transmitting packet-based voice information or packet-based data. The base station 12 is sometimes referred to as a Base Transceiver System (BTS).

The wireless communication system 10 operates in accordance with FDMA communication techniques and TDMA communication techniques. Frequency Division Multiple Access (FDMA) refers to a wireless communication technique in which an allocated frequency spectrum is divided into a plurality of smaller frequency "cells". Each cell of the allocated spectrum has a carrier signal that can be modulated with data. Each base station 12 typically operates in a different frequency cell of the allocated spectrum. For example, each base station 12 may be operated by a different service provider, and each respective service provider associated with a respective base station 12 may utilize its cell or cells to provide service to its users.

Time Division Multiple Access (TDMA) refers to a wireless communication technique in which a frequency cell is divided into several time slots. In systems implementing TDMA techniques, different wireless communications are transmitted during particular time slots, and in some cases, time slots may be reserved for reservation-based communications. In this manner, a single frequency cell may support multiple time division communication channels. TDMA techniques may be used within each cell associated with each base station 12.

One challenge in systems implementing FDMA and TDMA techniques, such as system 10, is the cell selection or acquisition process for subscriber unit 14. In the cell selection process, subscriber unit 14 identifies a desirable cell that can provide network access to subscriber unit 14. If the network provider of subscriber unit 14 operates only one base station 12, subscriber unit 14 should identify the cell associated with that base station as a desirable communication cell. On the other hand, if the network provider of subscriber unit 14 is operating two or more base stations 12, subscriber unit 14 should identify the cell with the highest received signal strength for that network provider. If the network provider of subscriber unit 14 is not operating base station 12, subscriber unit 14 should identify a cell based on other priorities. For example, if the network provider of subscriber unit 14 is not operating base station 12, subscriber unit 14 may select a cell operated by a different network provider with an appropriate and good roaming agreement. Other types of priorities may also be used.

In fig. 1, the illustrated components of the subscriber unit 14 are specifically those used in the cell selection process. There are many other components that are used for other functions, such as signal encoding and demodulation. However, for simplicity, the additional components are not illustrated.

Receiver/transmitter 20 receives wireless signals 18A-18C (collectively signals 18) from base station 12 via antenna 21. Receiver/transmitter 20 also performs various analog signal conditioning functions on the received signal, such as filtering or scaling the signal. Receiver/transmitter 20 separates the different signals associated with the various cells of system 10. Receiver/transmitter 20 then forwards the received signal to an analog-to-digital (a/D) converter 22, which samples the signal to produce a digital value, i.e., a digital signal, representative of the received analog signal. The digital signal is then passed from the a/D converter 22 to the control unit 24 for the control unit to implement the cell selection process described herein.

Control unit 24 may include a number of functional components, e.g., implemented in hardware, software, firmware, or similar elements, to implement the cell selection process. For example, the control unit 24 may include a power scan unit 26, a power estimator 28, an ID generator 30, and a cell selector 32. Control unit 24 may be implemented as a Digital Signal Processor (DSP) executing software modules, a programmable microprocessor, or discrete hardware components. Moreover, the control unit 24 may also be implemented in any combination of hardware, software, firmware, one or more programmable microprocessors, digital signal processors, or the like. Various components of the control unit 24 are illustrated herein for purposes of explanation, but may be integrated with other components, such as within hardware or software. If control unit 24 is implemented in software, a memory or other computer-readable medium (not shown) may be coupled to control unit 24 to store the software instructions loaded into control unit 24 for execution.

The power scan unit 26 scans the various cells of an allocated spectrum to identify different signals for different cells separated by the receiver/transmitter 20. For example, receiver/transmitter 20 may separate various signals associated with various cells, and in this case, power scanning unit 26 scans the separate signals to identify different signals and initiate subsequent processing of the signals. Furthermore, in GSM, the frequency bands around 900MHz and around 1800MHz are divided into about 548 frequency cells, each of which is about 200 KHz. In this case, receiver/transmitter 20 separates the signals associated with each of the 548 cells. The power scanning unit 26 scans the 548 cell to identify and distinguish the cells and then estimates the power of the cells.

In any case, the power estimator 28 measures and estimates the signal power of the various cells scanned by the power scanning unit 26. Power estimator 28 also maintains a list of the cells in which the estimated powers of the various cells are ordered from the highest power cell to the lowest power cell.

ID generator 30 uses the sorted list maintained by power estimator 28. Specifically, the ID generator starts from the highest power cell in the list and obtains the cell ID of the cell. In GSM, the cell ID acquisition process is a multi-step process that includes identifying the various channels or codes of a given cell. For example, for a given cell in GSM, ID generator 30 acquires a Frequency Correction Channel (FCCH) that can be used for coarse synchronization with the cell. ID generator 30 then acquires a Synchronization Channel (SCH) that provides basic timing information about the associated base station 12 associated with the respective cell. Once ID generator 30 has the SCH, it may decode an overhead channel, such as a broadcast channel (BCCH), to identify a Public Land Mobile Network (PLMN) code that may identify the network associated with the given cell.

In accordance with this disclosure, ID generator 30 may be designed to efficiently utilize processing time to accelerate the acquisition process of the cell. Specifically, once synchronization information (e.g., the FCCH and SCH) for a first cell of an FDMA system is acquired, ID generator 30 schedules the timing of the acquisition of cell ID information, e.g., the decoding of the BCCH and the identification of the PLMN code associated with the first cell. ID generator 30 then obtains synchronization information (e.g., the FCCH and SCH of a second cell of the FDMA system) prior to obtaining the cell ID information (e.g., the BCCH and PLMN code associated with the first cell).

In other words, rather than acquiring synchronization information for a cell and then waiting to acquire cell ID information for the cell, ID generator 30 may more efficiently utilize the processing time between acquiring synchronization information for a given cell and acquiring cell ID information. Specifically, ID generator 30 utilizes the time between the acquisition of synchronization information for a first cell and the acquisition of cell ID information for the first cell to acquire synchronization information for a second cell, and possibly a third cell, a fourth cell, a fifth cell, etc. In this way, the cell acquisition process for the subscriber unit 14 may be accelerated.

Cell selector 32 receives the generated network ID (e.g., the PLMN code obtained from each BCCH) and selects a desired cell for subsequent use by subscriber unit 14 in communications. Cell selector 32 may implement a priority scheme in which the highest power cell associated with a particular network is selected, but other cells may be selected if the cell associated with the particular network is not strong enough. For example, if the network provider of subscriber unit 14 is not operating any base stations 12, cell selector 32 may select a cell operated by a different network provider with an appropriate and good roaming agreement. The cell selector 32 then instructs the receiver/transmitter 20 to communicate with the base station of the selected cell in order to register for subsequent communication with the respective base station. Typically, preference is given to using a cell associated with the network provider of the subscriber unit 14. However, a selected cell must meet minimum power requirements for reliable communication.

Also, in accordance with the present invention, the cell selector 32 may also consider the possibility that a generated network ID is not associated with the highest power cell currently being processed. For example, in some cases, decoding of the BCCH for a second cell may be scheduled prior to decoding the BCCH for a first cell in accordance with the present invention, wherein the second cell has lower power than the first cell. In this case, because the first cell may be prioritized over the second cell, cell selector 32 may wait until decoding of the BCCH of the first (higher power) cell is performed before making the cell selection.

Fig. 2 is a flow chart illustrating a cell selection process implemented by subscriber unit 14. As shown in fig. 2, power scan unit 26 scans a cell of an FDMA spectrum (step 41), for example, after transmitter/receiver 20 has separated the signals of the different cells. The power estimator 28 then estimates the power of the different cells (step 42), possibly taking into account effects that tend to compromise the reliability of the power measurement of the power estimator 28.

Power estimator 28 classifies the cell according to its estimated power (step 43). In particular, power estimator 28 generates a list of cells with the estimated powers ordered from highest to lowest. ID generator 30 generates a network ID for the cell, step 44, and cell selector 32 selects a desired cell based on the network ID and the estimated power level, step 45. For example, ID generator 30 may utilize parallel processing techniques to generate network IDs starting from the highest power cell as described herein to accelerate the cell selection process. Once the cell selector 32 identifies a network ID associated with the service provider of the subscriber unit 14, the cell associated with that network ID can be selected, assuming it is the highest power cell for that service provider and the power level of that cell is high enough. At that point, the ID generation process may be terminated.

In conventional systems, the FCCH, SCH acquisition and BCCH decoding are performed for each cell in order of measured power to obtain the PLMN before moving to the next cell. However, a preferred method is to take advantage of the TDMA nature of GSM cells and schedule decoding of the BCCH to obtain the PLMN upon obtaining the FCCH and SCH for any given cell. If it is determined that the BCCH will not occur within X milliseconds after obtaining the FCCH and SCH for a given cell, the X milliseconds can be used to acquire the FCCH and SCH for the next cell in order of measured power.

This process may continue indefinitely, giving processing priority to any scheduled decoding of the BCCH for one cell, but using any unused processing time to acquire the FCCHs and SCHs for the other cells, and then queuing the BCCH decoding for the other cells in the scheduling scheme. For example, in GSM, the time between acquiring synchronization information for a given cell and acquiring the cell ID may take 1 second due to the repetitiveness of the messages needed to acquire the cell ID. On the other hand, the time required to acquire the synchronization information is generally less than 50 to 100 milliseconds. Thus, parallel acquisition of cell IDs can speed up the process of identifying a desirable cell for registering a subscriber unit.

Fig. 3 is a more specific exemplary block diagram of the power estimator 28, ID generator 30, and cell selector 32 of the subscriber unit 14 (fig. 1). Power estimator 28 measures and estimates the power of each cell in an FDMA system (e.g., GSM). Based on its power measurements, power estimator 28 maintains a list of different cells in which the estimated power is ordered from the highest power cell to the lowest power cell.

ID generator 30 receives input signals from a/D converter 20 and is designed to efficiently utilize processing time to accelerate the cell acquisition process. In this example, the ID generator 30 includes a scheduler 35, a cell timing unit (cell timing unit)36, and a cell ID acquisition unit (cell ID acquisition unit)37, but the functions of the components may be integrated with each other. ID generator 30 utilizes the ranking table (power-based ranking) of the cells maintained by power estimator 28. The scheduler 35 utilizes the TDMA nature of the received signal for each cell to coordinate the different phases of the cell acquisition process for each given cell.

Starting from the highest power cell of the ranking list of said cells maintained by the power estimator 28, the scheduler 35 invokes the cell timing unit 36 to obtain synchronization information. Cell timing unit 36 acquires synchronization information for the cell, e.g., in the case of GSM, this is the FCCH and SCH for the cell. In GSM, the acquisition of the FCCH and SCH typically takes less than about 100 milliseconds.

Based on the FCCH and SCH acquired for the current cell, scheduler 35 determines whether cell ID information (e.g., BCCH) for the cell exists. If there is cell ID information, the identification of the desired BCCH can be between 0 and 1 second, depending on the TDMA cycle of the cell. In accordance with this disclosure, scheduler 35 schedules decoding of the BCCH for the current cell and, if there is sufficient time before decoding the BCCH, the scheduler re-invokes cell timing unit 36 to acquire synchronization information for the next cell in the cell scheduling table maintained by power estimator 28 before invoking cell ID acquisition unit 37 to decode the BCCH for the first cell. Upon reaching the scheduled decoding time for the BCCH for the first cell, scheduler 35 invokes cell ID acquisition unit 37 to decode the BCCH. In this way, ID generator 30 may efficiently utilize processing time to speed up the cell acquisition process.

In other words, rather than acquiring synchronization information for a cell and then waiting to acquire cell ID information for the cell, ID generator 30 more efficiently utilizes the time between acquiring synchronization information for a given cell and acquiring cell ID information. Scheduler 35 coordinates the processing, gives processing priority to any scheduled decoding of the BCCH of one cell, but takes advantage of any unused processing time to acquire the FCCH and SCH of other cells, and then queues the decoding of the BCCH of the other cells in the scheduling scheme.

As described above, cell selector 32 receives the generated network ID (e.g., the PLMN code obtained from each BCCH) and selects a desired cell for use by subscriber unit 14 (fig. 1) in subsequent communications. Cell selector 32 may implement a priority scheme in which the highest power cell associated with a particular network is selected, but other cells may be selected if the cell associated with the particular network is not strong enough. For example, if the network provider of subscriber unit 14 is not operating base station 12, cell selector 32 may select a cell operated by a different network provider with an appropriate and good roaming agreement. The cell selector 32 then instructs the receiver/transmitter 30 to communicate with the base station of the selected cell to register with the selected cell for subsequent communication with the corresponding base station.

Also, in accordance with the present invention, the cell selector 32 may also consider the likelihood that the generated network ID is not associated with the highest power cell currently being processed. For example, in some cases, decoding of the BCCH for a second cell may be scheduled prior to decoding the BCCH for a first cell in accordance with the present invention, wherein the second cell has a lower power than the first cell. In this case, because the first cell may be prioritized over the second cell, cell selector 32 may wait until decoding of the BCCH of the first (higher power) cell is performed before making the cell selection.

Fig. 4 is a flow chart illustrating a process implemented within subscriber unit 14 in accordance with the present invention. As illustrated in fig. 4, power estimator 28 ranks the cells of an FDMA system according to power (step 61). Starting from the highest power cell, ID generator 30 searches for synchronization information for the next cell (step 62). For example, scheduler 35 may invoke cell timing unit 36 to obtain the FCCH and SCCH of the cell. Based on the synchronization information, scheduler 35 determines whether cell ID information (e.g., BCCH) for the cell exists (step 63). If so (yes branch of step 63), scheduler 35 schedules cell ID acquisition for the cell based on the synchronization information for the cell (step 64).

At this point, if scheduler 35 determines that none of the cells scheduled for cell ID acquisition (no branch of step 65) are in a state to be decoded, the process is repeated for the next cell (i.e., the next maximum power cell) (steps 62-65). In other words, rather than acquiring synchronization information for a cell and then waiting to acquire cell ID information for that cell, ID generator 30 may more efficiently utilize the time between acquiring synchronization information and acquiring cell ID information for a given cell. Specifically, ID generator 30 utilizes the time between the acquisition of synchronization information for a first cell and the acquisition of cell ID information for the first cell to acquire synchronization information for a second cell and possibly a third cell, a fourth cell, a fifth cell, and so on. In this way, the cell acquisition process for the subscriber unit 14 may be accelerated.

Upon reaching the scheduled time to acquire cell ID information for a given one of the cells (yes branch of step 65), scheduler 35 invokes cell ID acquisition unit 37 to acquire the cell ID information (step 66), which may include the PLMN code for the scheduled cell. In this case, cell ID acquisition unit 37 acquires the cell ID information (i.e., the PLMN code for the scheduled cell) and scheduler 35 updates a list of possible cells available for communication to include the cell identified by the PLMN code for the scheduled cell (step 67). Specifically, the cell ID acquisition unit decodes the BCCH of the given cell to acquire the PLMN code.

Cell selector 32 determines whether a desirable cell can be identified from the list of possible cells maintained in scheduler 35, step 68, and, if so, causes receiver/transmitter 20 (fig. 1) to register subscriber unit 14 in that cell, step 69. The subscriber unit may then use the desired cell for communication.

In accordance with the present invention, in some cases, a desirable cell may not be identified after acquiring cell ID information for a given cell (no branch of step 68), for example, if a cell with higher power than the given cell is still scheduled for cell ID acquisition. In this manner, cell selector 32 may consider the likelihood that the generated network ID is not associated with the highest power cell currently being processed. For example, decoding of a BCCH for a second cell may be scheduled prior to decoding of a BCCH for a first cell, where the second cell has lower power than the first cell. In this case, the process of fig. 4 continues until decoding of the BCCH of the first (higher power) cell is performed before cell selection is made, since the first cell may be prioritized over the second cell.

Another scenario in which parallel acquisition and decoding as described herein may be utilized is a scheme in which a user manually instructs the subscriber unit to display all available networks. In this case, the subscriber unit will not stop acquiring the PCCH and SCH in parallel and decoding the BCCH until the subscriber unit identifies all cells above the threshold power level. Conversely, in normal acquisition, the subscriber unit typically stops decoding once the desired network is identified. However, when the user manually instructs the subscriber unit to display all available networks, decoding typically continues even though a particular network or cell has been identified.

Fig. 5 is another flow diagram according to an embodiment of the present invention in which a user manually instructs subscriber unit 14 to display all available networks. As illustrated in fig. 5, power estimator 28 ranks the cells of an FDMA system according to power (step 71). Starting from the highest power cell, ID generator 30 searches for synchronization information for the next cell (step 72). For example, scheduler 35 may invoke cell timing unit 36 to acquire the FCCH and SCCH of the cell. Based on the synchronization information, scheduler 35 determines whether cell ID information (e.g., a BCCH) for the cell exists (step 73). If so (yes branch of step 73), scheduler 35 schedules cell ID acquisition for the cell based on the synchronization information for the cell (step 74).

At this point, if scheduler 35 determines that none of the cells scheduled for cell ID acquisition (no branch of step 75) are in a state to be decoded, the process is repeated for the next cell (i.e., the next maximum power cell) (steps 72 through 75). In other words, rather than acquiring synchronization information for a cell and then waiting to acquire cell ID information for that cell, ID generator 30 may more efficiently utilize the time between acquiring synchronization information for a given cell and acquiring cell ID information. Specifically, ID generator 30 utilizes the time between acquiring synchronization information of a first cell and acquiring cell ID information of the first cell to acquire synchronization information of a second cell and possibly a third cell, a fourth cell, a fifth cell, and so on. In this way, the cell acquisition process for the subscriber unit 14 may be accelerated.

Upon reaching the scheduled time to acquire cell ID information for a given one of the cells (yes branch of 75), scheduler 35 invokes cell ID acquisition unit 37 to acquire the cell ID information, which may include the PLMN code for the scheduled cell (76). In this case, cell ID acquisition unit 37 acquires the cell ID information (i.e., the PLMN code for the scheduled cell), and scheduler 35 updates a list of possible cells available for communication to include the cell identified by the PLMN code for the scheduled cell (step 77).

Cell selector 32 determines whether the top N cells of scheduler 35 have been decoded. If the top N cells have not been decoded (no branch of step 78), the process continues, for example, if another high power cell is still scheduled for cell ID acquisition. The top N cells refer to cells above some threshold power level that make the cells candidate networks for subscriber unit 14. Once the top N cells in scheduler 35 have been decoded, subscriber unit 14 may display a list of candidate networks or cells to the user (step 79). The user may then manually select a desired cell from the list of candidate cells and manually register subscriber unit 14 within that cell for communication. By performing parallel acquisition and decoding during generation of the candidate cell list, the process may be accelerated relative to common techniques for generating candidate cell lists.

Several embodiments have been described herein. In particular, various techniques have been described herein for more efficiently utilizing processing time to accelerate the acquisition process of the cell. The techniques may be implemented in hardware, software, firmware, or similar elements of a subscriber unit to implement the cell selection described herein. Examples of hardware implementations may include implementations in the following hardware: a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA), a programmable logic device, a specifically designed hardware component, or any combination thereof. Furthermore, one or more of the techniques described herein may be partially or fully implemented in software. In this case, a computer-readable medium may store or otherwise comprise computer-readable instructions (i.e., program code) that are executable by a processor or DSP of a subscriber unit to implement one or more of the techniques described herein.

For example, the computer-readable medium may comprise: random Access Memory (RAM), Read Only Memory (ROM), non-volatile random access memory (NVRAM), Electrically Erasable Programmable Read Only Memory (EEPROM), flash memory, or the like, of the control unit 12 coupled to the user unit 14. In this case, control unit 24 may comprise a processor or DSP that executes various software modules stored in the computer-readable medium. Many other modifications may be made to the embodiments without departing from the spirit and scope of the invention. Accordingly, these and other embodiments are within the scope of the following claims.

Claims (36)

1. A method, comprising:

acquiring synchronization information of a first cell of a Frequency Division Multiple Access (FDMA) system;

scheduling a time to acquire cell Identification (ID) information associated with the first cell based on the synchronization information of the first cell; and

acquiring synchronization information of a second cell of the FDMA system prior to acquiring the cell ID information associated with the first cell.

2. The method of claim 1, further comprising: acquiring the synchronization information of the second cell of the FDMA system prior to acquiring the cell ID information associated with the first cell only if there is sufficient time to acquire the synchronization information of the second cell prior to the scheduled time to acquire the cell ID information associated with the first cell.

3. The method of claim 1, further comprising:

scheduling a time to acquire the cell ID information associated with the second cell based on the synchronization information of the second cell; and

acquiring synchronization information of a third cell of the FDMA system prior to acquiring the cell ID information associated with the second cell.

4. The method of claim 3, further comprising: acquiring synchronization information of the third cell of the FDMA system prior to acquiring the cell ID information associated with the first cell.

5. The method of claim 1, further comprising: after acquiring synchronization information of the second cell, the cell ID information associated with the first cell is acquired at the scheduled time.

6. The method of claim 5, further comprising: selecting or rejecting the first cell based on the cell ID information associated with the first cell.

7. The method of claim 6, further comprising: registering in the first cell when the first cell is selected according to the cell ID information associated with the first cell.

8. The method of claim 1, wherein the FDMA system comprises a global system for mobile communications (GSM) system, acquiring the synchronization information comprises acquiring a Frequency Correction Channel (FCCH) and a Synchronization Channel (SCH), and acquiring the cell ID information comprises acquiring a Public Land Mobile Network (PLMN) code from a broadcast channel (BCCH).

9. The method of claim 1, further comprising: generating a list of available networks including the first cell and the second cell based on the cell ID information associated with the first cell and the cell ID information associated with the second cell.

10. A subscriber unit of a Frequency Division Multiple Access (FDMA) system comprising:

a receiver that receives a first signal associated with a first cell of the FDMA system and a second signal associated with a second system of the FDMA system; and

a control unit to acquire synchronization information of the first cell, schedule a time to acquire cell Identification (ID) information associated with the first cell based on the synchronization information of the first cell, and acquire synchronization information of the second cell before acquiring the cell ID information associated with the first cell.

11. The subscriber unit of claim 10, wherein the control unit acquires the synchronization information of the second cell of the FDMA system prior to acquiring the cell ID information associated with the first cell only if there is sufficient time to acquire the synchronization information of the second cell prior to the scheduled time to acquire the cell ID information associated with the first cell.

12. The subscriber unit of claim 10, wherein the control unit schedules a time to acquire cell ID information associated with the second cell based on the synchronization information of the second cell and acquires synchronization information of a third cell of the FDMA system prior to acquiring the cell ID information associated with the second cell.

13. The subscriber unit of claim 12, wherein the control unit acquires synchronization information of the third cell of the FDMA system prior to acquiring the cell ID information associated with the first cell.

14. The subscriber unit of claim 10, wherein the control unit obtains the cell ID information associated with the first cell at the scheduled time.

15. The subscriber unit of claim 14, wherein the control unit selects or rejects the first cell based on the cell ID information associated with the first cell.

16. The subscriber unit of claim 10, wherein the control unit causes the subscriber unit to register in the first cell when the first cell is selected based on the cell ID information associated with the first cell.

17. The subscriber unit of claim 10, wherein the FDMA system comprises a global system for mobile communications (GSM) system, acquiring the synchronization information comprises acquiring a Frequency Correction Channel (FCCH) and a Synchronization Channel (SCH), and acquiring the cell ID information comprises acquiring a Public Land Mobile Network (PLMN) code from a broadcast channel (BCCH).

18. A computer-readable medium comprising instructions to cause a subscriber unit of a Frequency Division Multiple Access (FDMA) system to:

acquiring synchronization information of a first cell of the FDMA system;

scheduling a time to acquire cell Identification (ID) information associated with the first cell based on the synchronization information of the first cell; and

acquiring synchronization information of a second cell of the FDMA system prior to acquiring the cell ID information associated with the first cell.

19. The computer-readable medium of claim 18, further comprising instructions that cause the subscriber unit to acquire the synchronization information for the second cell of the FDMA system prior to acquiring the cell ID information related to the first cell only if there is sufficient time to acquire the synchronization information for the second cell prior to the scheduled time to acquire cell ID information associated with the first cell.

20. The computer-readable medium of claim 18, further comprising instructions that cause the subscriber unit to schedule a time to acquire cell ID information associated with the second cell based on the synchronization information of the second cell and acquire synchronization information of a third cell of the FDMA system prior to acquiring the cell ID information associated with the second cell.

21. The computer-readable medium of claim 20, further comprising instructions that cause the subscriber unit to acquire synchronization information of the third cell of the FDMA system prior to acquiring the cell ID information associated with the first cell.

22. The computer-readable medium of claim 18, further comprising instructions that cause the subscriber unit to acquire the cell ID information associated with the first cell at the scheduled time.

23. The computer-readable medium of claim 22, further comprising instructions that cause the subscriber unit to select or reject the first cell based on the cell ID information associated with the first cell.

24. The computer-readable medium of claim 23, further comprising instructions that cause the user to register in the first cell when the first cell is selected according to the cell ID information associated with the first cell.

25. The computer-readable medium of claim 18, wherein the FDMA system comprises a global system for mobile communications (GSM) system, acquiring the synchronization information comprises acquiring a Frequency Correction Channel (FCCH) and a Synchronization Channel (SCH), and acquiring the cell ID information comprises acquiring a Public Land Mobile Network (PLMN) code from a broadcast channel (BCCH).

26. A subscriber unit of a Frequency Division Multiple Access (FDMA) system comprising:

means for obtaining synchronization information for a first cell of the FDMA system;

means for scheduling a time to acquire cell Identification (ID) information associated with the first cell based on the synchronization information of the first cell; and

means for acquiring synchronization information of a second cell of the FDMA system prior to acquiring the cell ID information associated with the first cell.

27. The subscriber unit of claim 26, further comprising means for acquiring the synchronization information of the second cell of the FDMA system prior to acquiring the cell ID information associated with the first cell only if there is sufficient time to acquire the synchronization information of the second cell prior to the scheduled time to acquire cell ID information associated with the first cell.

28. The subscriber unit of claim 26, further comprising:

means for scheduling a time to acquire cell ID information associated with the second cell based on the synchronization information of the second cell; and

means for acquiring synchronization information of a third cell of the FDMA system prior to acquiring the cell ID information associated with the second cell.

29. The subscriber unit of claim 28, further comprising means for acquiring synchronization information of the third cell of the FDMA system prior to acquiring the cell ID information associated with the first cell.

30. The subscriber unit of claim 26, further comprising means for acquiring the cell ID information associated with the first cell at the scheduled time.

31. The subscriber unit of claim 30, further comprising means for selecting or rejecting the first cell based on the cell ID information associated with the first cell.

32. The subscriber unit of claim 31, further comprising means for registering in the first cell when the first cell is selected according to the cell ID information associated with the first cell.

33. The subscriber unit of claim 26, wherein the FDMA system comprises a global system for mobile communications (GSM) system, acquiring the synchronization information comprises acquiring a Frequency Correction Channel (FCCH) and a Synchronization Channel (SCH), and acquiring the cell ID information comprises acquiring a Public Land Mobile Network (PLMN) code from a broadcast channel (BCCH).

34. A method for a global system for mobile communications (GSM), comprising:

acquiring a Frequency Correction Channel (FCCH) and a Synchronization Channel (SCH) of a first cell;

decoding a broadcast channel (BCCH) associated with the first cell according to the SCH of the first cell scheduling a time; and

acquiring a FCCH and a SCH of a second cell prior to decoding the BCCH associated with the first cell.

35. The method of claim 34, further comprising: acquiring the FCCH and SCH of the second cell prior to decoding the BCCH associated with the first cell only if there is sufficient time to acquire the FCCH and SCH of the second cell prior to acquiring the scheduled time of the BCCH associated with the first cell.

36. The method of claim 34, wherein decoding the BCCH associated with the first cell comprises obtaining a Public Land Mobile Network (PLMN) code for the first cell from the BCCH associated with the first cell.