DESC:FORM 2
THE PATENTS ACT, 1970
[39 of 1970]
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(Section 10; Rule 13)

METHOD FOR CELL RESELECTION IN A TIME DIVISION SYNCHRONOUS CODE DIVISION MULTIPLE ACCESS (TD-SCDMA) SYSTEM

SAMSUNG R&D INSTITUTE INDIA – BANGALORE Pvt. Ltd.
# 2870, ORION Building, Bagmane Constellation Business Park,
Outer Ring Road, Doddanakundi Circle,
Marathahalli Post,
Bangalore -560037, Karnataka, India
Indian Company

The following Specification particularly describes the invention
and the method it is being performed
FIELD OF THE INVENTION
The present invention generally relates to communication systems and particularly relates to a method for performing reselection of a cell to camp on in a wireless communication system.

BACKGROUND OF THE INVENTION

In a Global System for Mobile Communications (GSM) system, after selecting a public land mobile network identity (PLMN), a user equipment (UE) may perform a cell selection procedure and a cell reselection procedure in order to use related network services. The cell selection procedure allows the UE to quickly camp on a serving cell, thereby receiving system information from the PLMN, establishing radio resource control (RRC) links, accessing network via control channels, and receiving/replying paging messages. The cell reselection procedure allows the UE to camp on another target cell having better signal quality than the current serving cell. The cell selection procedure and the cell reselection procedure herein can only be performed on suitable cells or acceptable cells. The “suitable” cell is a cell from which the UE can receive service, and which satisfies a set of suitability criteria that a cell must meet in order to be a “suitable cell”, as per the defined GSM standards.

Currently, as part of the GSM standard, a mobile communication device performing the cell selection must camp on the best available cell in the vicinity. To satisfy this requirement, the mobile communication device typically performs an initial power scan over the frequency band to measure the signal strength of the cells in the area and generates a list of cells in decreasing order of the measured received signal strengths for the cells. The mobile communication device then goes through an ordered list of cells, selecting each cell in order to find the first cell in the ordered list that meets the set of suitability criteria. When a suitable cell is found, the mobile communication device performs registration with the cell, if necessary. The mobile communication device then camps on the cell to communicate with a mobile network to which the mobile communication device is subscribed.

However, in a conventional Time Division Synchronous Code Division Multiple Access (TD-SCMDA), where frame boundary of cells are time aligned, it is possible to have high interference on TimeSlot-0 (TS-0) where broadcast channels (beacon channels) are transmitted. In the interference conditions if cell selection is performed just based on conventional Received Signal Strength Indication (RSSI) and Received Signal Code Power (RSCP) measurements, it is possible to encounter failure to read BCH (Broadcast) channel and fail to cell selection, which can cause delay of cell selection. Further the BCH read failure on the selected cell may cause delay in a cell camp on procedure. Moreover, the user experience can be degraded during cell search after OOS (Out Of Service) while Circuit Switched/Packet Switched (CS/PS) call is in progress and can cause call drop.

In view of the foregoing, there is a need of an efficient cell selection and cell reselection procedure and sequence of the search operations which will make cell searching optimal and reliable. The above mentioned shortcomings, disadvantages and problems are addressed herein and which will be understood by reading and studying the following specification.

SUMMARY OF THE INVENTION
The various embodiments of the present invention disclose a method and apparatus for providing cell selection in Time Division Synchronous Code Division Multiple Access (TD-SCDMA) systems. The method comprises of generating, by a User Equipment (UE), an ordered list of Universal Absolute Radio Frequency Channel Numbers (UARFCNs) based on a Received Signal Strength Indicator (RSSI) measurements associated with one or more UARFCNs, calculating a Synchronization Downlink (SyncDL) correlation energies associated with the UARFCNS, arranging the one or more UARFCNs based on the RSSI and the associated SyncDL correlation energies, scanning the one or more UARFCNs to detect if one or more serving cells are available to be camped on and selecting a serving cell based on a Signal to noise ratio (SNR) threshold associated with the UARFCN.

According to an embodiment of the present invention, scanning the one or more UARFCNs comprises of performing an RSSI scan on each UARFCN in the ordered list to determine whether each RSSI scan is greater than a predetermined Signal to Noise Ratio (SNR) threshold.

Embodiments herein further disclose a for providing Division Multiple Access (TD-SCDMA) systems, the method comprises of selecting a plurality of UTRA Absolute Radio Frequency Channel Numbers (UARFCNs) from a database based on a previously camped cell information, detecting a Received Signal Strength Indication (RSSI) and Synchronization Downlinks (SyncDL) correlation energies associated with the RSSI, arranging the plurality of UARFCNs into a first list and a second list based on a Location Area Update (LAU) information, scanning the plurality of UARFCNs to detect if one or more cells are available for the first list and the second list and selecting a serving cell present in the UARFCN based on a Signal to Noise ratio (SNR) threshold associated the serving cell.

According to an embodiment of the present invention, selecting a serving cell to be camped on comprises of selecting at least three UARFCN cell set having a high signal frequency from the plurality of UARFCNs, performing an IMS Centralized Service (ICS) on the first UARFCN in the cell set, performing a BCH read on cells of the first UARFCN which are above a first SNR threshold and camping on the serving cell of the first UARFCN if the BCH read is success.

According to an embodiment of the present invention, the method further comprises of checking if the ICS is pending for any UARFCN in the cell set if the BCH read is not successful, performing ICS on the UARFCN if UARFCN is left in the set and performing the BCH read on the serving cells of the UARFCN which are above the first SNR threshold.

According to an embodiment of the present invention, the method further comprises of sorting the plurality of serving cells across one or more UARFCNs of the set if no UARFCNs are present in the set for ICS, performing the BCH read on one or more serving cells having a carrier frequency above a second SNR threshold and identifying the serving cell for camping on if the BCH read is success. Further the method comprises of checking if any UARFCN is left in the list, if the BCH read is not success, selecting a next set of three UARFCNS for identifying the camp on cell if any UARFCN is left in the list and performing a full band frequency search if no ARFCNs is left in the list.

According to an embodiment of the present invention, the UE performs a carrier frequency search to identify the ordered list of UARFCNs and the SyncDL correlation energies.

The foregoing has outlined, in general, the various aspects of the invention and is to serve as an aid to better understand the more complete detailed description which is to follow. In reference to such, there is to be a clear understanding that the present invention is not limited to the method or application of use described and illustrated herein. It is intended that any other advantages and objects of the present invention that become apparent or obvious from the detailed description or illustrations contained herein are within the scope of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The other objects, features and advantages will occur to those skilled in the art from the following description of the preferred embodiment and the accompanying drawings in which:

Figure 1 is a flow diagram illustrating a method of enabling cell reselection in a TD-SCDMA system, according to an embodiment of the present invention.

Figure 2 is a flow diagram illustrating a method of enabling cell reselection in a TD-SCDMA system, according to another embodiment of the present invention.

Figure 3 is a flow chart illustrating a method of TD-SCDMA UARFCNs cell selection based on SYNC-DL correlation energy of best path, according to an embodiment of the present invention.

Figure 4 is a flow chart illustrating a method of enabling a suitable serving cell selection from a set of shortlisted UARFCNs, according to an embodiment of the present invention.

Although specific features of the present invention are shown in some drawings and not in others, this is done for convenience only as each feature may be combined with any or all of the other features in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a method and apparatus for providing cell selection in Time Division Synchronous Code Division Multiple Access (TD-SCDMA) systems. In the following detailed description of the embodiments of the invention, reference is made to the accompanying drawings that form a part hereof, and in which are shown by way of illustration specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that changes may be made without departing from the scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims.

The specification may refer to “an”, “one” or “some” embodiment(s) in several locations. This does not necessarily imply that each such reference is to the same embodiment(s), or that the feature only applies to a single embodiment. Single features of different embodiments may also be combined to provide other embodiments.

As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless expressly stated otherwise. It will be further understood that the terms “includes”, “comprises”, “including” and/or “comprising” when used in this specification, specify the presence of stated features, integers, steps, operations, elements and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. As used herein, the term “and/or” includes any and all combinations and arrangements of one or more of the associated listed items.

Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

The present invention provides a system and method for providing cell selection in Time Division Synchronous Code Division Multiple Access (TD-SCDMA) systems. Various embodiments are described in the present disclosure to describe the working of the method, but not limiting to the scope of the present invention.

The embodiments herein and the various features and advantages details thereof are explained more fully with reference to the non-limiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein can be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.

According to an embodiment of the present invention, a method for providing cell selection in Time Division Synchronous Code Division Multiple Access (TD-SCDMA) systems is described herein. The method comprises step of generating an ordered list of Absolute Radio Frequency Channel Numbers (ARFCNs) with received signal strength values that exceed a received signal strength threshold in a decreasing order of received signal strengths. User equipment (UE) receives ARFCNs from one or more cells present within the location range, along with associated information. In an embodiment of the present invention, in case of partial cell search, the associated information can be at least one of, but not limited to, previous inter frequency UARFCNs, N-freq UARFCNs list stored at UE, which is received in sib information/Measurement Control, any DL configuration messages that includes N-frequency UARFCN information and the like. In another embodiment of the present invention, in case of complete cell search, searcher indicates scanning all the UARFCNs present in a given band as the associated information, without departing from the scope of the invention. The UE comprises of a threshold value for received signal strength and intends to identify cells with threshold received signal strength. Thus, upon receiving ARFCNs, the UE can generate a list of ARFCNs, wherein the ARFCNs are arranged in decreasing order of the received signal strength, which are more than threshold received signal strength.

Further, the method comprises step of selecting one or more Universal Absolute Radio Frequency Channel Numbers (UARFCNs), from one or more supported frequency bands. Upon generating the list of ARFCNs, the UE can identify which frequency band supports the transfer of data packets easily. Various processes are available for identifying the suitable frequency band, and the person having ordinarily skilled in the art can use any of the known process, without departing from the scope of the invention. Based on the selected frequency band, one or more UARFCNs can be selected.

Further, the method comprises step of detecting a Received Signal Strength Indication (RSSI) and Synchronization Downlinks (SyncDL) and correlation energies associated with the RSSI and SyncDL. Based on the generated list of ARFCNs, RSSI and SyncDL can be detected. Further, the correlation energies associated with the RSSI and SyncDL can also be detected, which helps to identify the strength of the frequency bands.

Further, the method comprises step of scanning the one or more UARFCNs based on the RSSI and SyncDL correlation energies. Based on the obtained correlation energies of RSSI and SyncDL, the one or more UARFCNs can be scanned to identify the suitable frequency band for camping.

Further, the method comprises step of identifying a serving cell to be camped on based on a calculated cell suitability criteria, wherein the cell suitability criteria is a signal to noise ratio (SNR) threshold associated with the identified serving cell. The scanning of the UARFCNs can be based on cell suitability criteria, wherein the cell suitability criteria is a signal to noise ratio (SNR) threshold associated with the identified serving cell. Upon performing scanning, based on the calculated cell suitability criteria, the UE can identify the serving cell which is optimum for camping, and thus provides easy and quick camping to the UE on the move.

According to another embodiment of the present invention, a method for providing cell selection in Time Division Synchronous Code Division Multiple Access (TD-SCDMA) systems is described herein. According to the present invention, the method comprises steps of selecting a plurality of UTRA Absolute Radio Frequency Channel Numbers (UARFCNs) from a database based on previously camped cell information. The user equipment (UE) maintains a database of all the previously camped cell information, wherein the cell information comprises of information such as, but not limited to, UARFCN, ARFCN, broadcast channel (BCH), received signal code power (RSCP) measurements, and the like. Based on the available database, the UE can select one or more UARFCNs associated with the one or more previously camped cells from the database.

Further, the method comprises step of detecting a Received Signal Strength Indication (RSSI) and Synchronization Downlinks (SyncDL) and correlation energies associated with the RSSI and SyncDL. For the selected one or more UARFCNs, the UE can detect the RSSI and SyncDL and further can detect the correlation energies associated with the RSSI and SyncDL of selected UARFCNs.

Further, the method comprises step of arranging the plurality of UARFCNs into a first list and a second list based on Location Area Update (LAU) information. The UE can categorize and create two lists, first list and the second list. Based on the location area information (LAI) and location area update (LAU), the UE can arrange the selected UARFCNs in first list and the second list, without departing from the scope of the invention.

Further, the method comprises step of scanning the plurality of UARFCNs to detect if one or more cells are available for the first list and the second list. After updating the first list and the second list, the UE can further scans among other available UARFCNs, which are not arranged in either the first list and the second list, any UARFCNs available which can be arranged in the first list and the second list.

Further, the method comprises step of selecting a serving cell to be camped on based on a calculated cell suitability criteria. Based on the available first list and the second list, the UE can apply the cell suitability criteria on the available UARFCNs and select the serving cell on which the UE can be camped on, wherein the cell suitability criteria is the serving cell present in UARFCN next to a Broadcasting Channel (BCH) and a Signal to Noise ratio (SNR) threshold associated the serving cell.

According to an embodiment of the present invention, selecting a serving cell to be camped on comprises step of selecting at least three UARFCN cell set having a high signal frequency from the plurality of UARFCNs. Of all the selected UARFCNs, three UARFCNs with high signal frequency can be selected. According to an embodiment of the present invention, the three UARCNs with highest signal frequency can be selected based on detected RSSI, SyncDL and correlation energies of the RSSI and SyncDL, without departing from the scope of the inveniton.

The method of selecting the serving cell further comprises of performing an initial cell search (ICS) on the first UARFCN in the cell set. Of the selected three UARFCNs, the UE can perform ICS on the UARFCN in the cell set. Further, the method comprises step of performing a broadcast channel (BCH) read on cells of the first UARFCN which are above a first SNR threshold. Further, if the BCH read is success, then the method comprises of camping on the serving cell of the first UARFCN.

According to an embodiment of the present invention, if the BCH read is not successful, then the method further comprises step of checking if ICS is pending for any UARFCN in the cell set. If any ICS is pending for any UARFCN in the cell set, then the method comprises performing ICS on the UARFCN left in the cell set. Based on the ICS performed on the pending UARFCNs, the UE can perform the BCH read on the serving cells of the UARFCN, which are above the first SNR threshold.

According to another embodiment of the present invention, if the UARFCN is not left in the set for ICS, then the method further comprises step of sorting the plurality of serving cells across one or more UARFCNs of the set. Further, the method comprises of performing the BCH read on one or more serving cells having a carrier frequency above a second SNR threshold. If the BCH read is success, then the method comprises step of identifying the serving cell for camping on.

According to another embodiment of the present invention, if the BCH read is not success the method further comprises step of checking if any UARFCN is left in the list. If any UARFCN is left in the list, then the UE can select a next set of three UARFCNS for identifying cell on which the UE can camp on. But, if no ARFCNs are left in the list, then the UE can perform a full band frequency search.

According to an embodiment of the present invention, a Local Area Identity (LAI) of the carrying cell is compared across the UARFCNs with the SNR thresholds before selecting the cell based on SYNC DL with carrier frequency search to avoid unwanted cell selection.

Figure 1 is a flow diagram 100 illustrating a method of enabling cell reselection in a TD-SCDMA system, according to an embodiment of the present invention. According to the flow diagram 100, at step 102, user equipment (UE) generates an ordered list of Absolute Radio Frequency Channel Numbers (ARFCNs) based on a Received Signal Strength Indicator (RSSI) measurements associated with one or more UARFCNs. At step 104, the UE calculates a Synchronization Downlink (SyncDL) correlation energies associated with the UARFCNS. At step 106, the one or more UARFCNs are arranged based on the RSSI and the associated SyncDL correlation energies. At step 108, the one or more UARFCNs are then scanned to detect if one or more serving cells are available to be camped on. If serving cells are available, then select a serving cell based on a Signal to noise ratio (SNR) threshold associated with the UARFCN to be camped on at step 110.

Figure 2 is a flow diagram 200 illustrating a method of enabling cell reselection in a TD-SCDMA system, according to another embodiment of the present invention. According to the flow diagram 200, at step 202, user equipment (UE) selects a plurality of UTRA Absolute Radio Frequency Channel Numbers (UARFCNs) from a database based on previously camped cell information. Further, at step 204, a Received Signal Strength Indication (RSSI) and Synchronization Downlinks (SyncDL) are detected along with correlation energies associated with the RSSI and SyncDL. At step 206, the pluralities of UARFCNs are arranged into a first list and a second list based on Location Area Update (LAU) information. At step 208, the pluralities of UARFCNs are scanned to detect if one or more cells are available for the first list and the second list. Further, at step 210, a serving cell to be camped on is selected based on calculated cell suitability criteria.

Figure 3 is a flow chart 300 illustrating a method of TD-SCDMA UARFCNs cell selection based on SYNC-DL correlation energy of best path, according to an embodiment of the present invention. According to the flow chart 300, at step 302, cell selection process is initiated by user equipment (UE). At step 304, the UE checks whether partial cell search has to be conducted or complete cell search has to be conducted. If the UE wishes to perform partial search, then at step 306, a UARFCN list can pre generated, wherein the UARFCN list comprises of one or more previous UARFCNs, inter frequency UARFCNs and stored UARFCNs from a database. If the UE wishes to perform complete search, then at step 308, a UARFCN list can pre generated, wherein the UARFCN list comprises of UARFCNs present in the complete band.

The UARFCN list generated from partial cell search process at step 306 or from complete cell search process at step 308 can be processed further at step 310, wherein a request is being sent to physical layer for performing carrier frequency scan. Based on the received request, at step 312, the physical layer provides scan results, wherein the scan results received by the UE comprise of RSSI, SyncDL, along with correlation energies of the RSSI and SyncDL. Based on the received information from the physical layer, at step 314, the UE sorts all the UARFCNs based on correlation energies of the best SyncDL.

At step 316, the UE checks whether the RSSI of the UARFCNs is more than threshold RSSI. Based on the comparison, the UE discards all the UARFCNs whose RSSI is less than threshold RSSI. At step 318, the UE checks whether cell update search is to be performed or initial cell search is to be performed. If cell update search is to be performed, then at step 320, the UE checks whether for each UARFCN, the SyncDL belongs to current location area update (LAU). If yes, then at step 322, the UARFCN is added to a first list. If no, then at step 324, the UARFCN is added to a second list. If the UE wishes to perform initial cell search, then the process directly moves to step 324, wherein the UARFCN is added to the second list. At step 326, the UE proceeds further with cell scan and camp on procedure.

Figure 4 is a flow chart 400 illustrating a method of enabling a best serving cell selection from a set of shortlisted UARFCNs, according to an embodiment of the present invention. According to the flow chart 400, at step 402, user equipment (UE) selects best three UARFCNs set from a current list of available UARFCNs. At step 404, the UE performs initial cell search (ICS) on first UARFCN from the selected set of three UARFCNs. At step 406, broadcast channel (BCH) read on is performed on cells of UARFCN having value above than first threshold SNR SNR_THRES1. At step 408, the UE checks whether BCH read on is successful or not. If yes, then at step 410, he UE camps on the cell with selected UARFCN. If no, then at step 412, the UE checks whether any ARFCNs are left in set for ICS.

If there are any ARFCNs left for ICS, then at step 414, the UE performs ICS on next AFCRN in the set. For the selected next ARFCNs in the set, BCH read on can be performed at step 406. If no, then at step 416, all cells across all ARFCNs in the set are sorted. At step 418, BCH read on can be performed on the selected ARFCNs which are above second threshold value of SNR SNR_THRES2.

At step 420, the UE checks whether BCH is successful or not. If yes, then at step 410, the UE camps on the cell with the selected ARFCN. If no, then at step 422, the UE further checks whether any ARFCN left in the list. If yes, then at step 424, the UE selects the next set of three UARFCNs and proceeds further to set 404 for performing ICS. If no, then at step 426, the UE performs full band search.

In the following detailed description of the embodiments of the invention, reference is made to the accompanying drawings that form a part hereof, and in which are shown by way of illustration specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that changes may be made without departing from the scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims.
,CLAIMS:
1. A method for providing cell selection in Time Division Synchronous Code Division Multiple Access (TD-SCDMA) systems, the method comprising:
generating, by a User Equipment (UE), an ordered list of Universal Absolute Radio Frequency Channel Numbers (UARFCNs) based on a Received Signal Strength Indicator (RSSI) measurements associated with one or more UARFCNs;
calculating a Synchronization Downlink (SyncDL) correlation energies associated with the UARFCNS;
arranging the one or more UARFCNs based on the RSSI and the associated SyncDL correlation energies;
scanning the one or more UARFCNs to detect if one or more serving cells are available to be camped on; and
selecting a serving cell based on a Signal to noise ratio (SNR) threshold associated with the UARFCN.

2. The method of claim 1, wherein scanning the one or more UARFCNs comprises of :
performing an RSSI scan on each UARFCN in the ordered list to determine whether each RSSI scan is greater than a predetermined Signal to Noise Ratio (SNR) threshold.

3. A method for providing cell selection in Time Division Synchronous Code Division Multiple Access (TD-SCDMA) systems, the method comprising:
selecting a plurality of UTRA Absolute Radio Frequency Channel Numbers (UARFCNs) from a database based on a previously camped cell information;
detecting a Received Signal Strength Indication (RSSI) and Synchronization Downlinks (SyncDL) correlation energies associated with the RSSI;
arranging the plurality of UARFCNs into a first list and a second list based on a Location Area Update (LAU) information;
scanning the plurality of UARFCNs to detect if one or more cells are available for the first list and the second list; and
selecting a serving cell present in the UARFCN based on a Signal to Noise ratio (SNR) threshold associated the serving cell.

4. The method of claim 3, wherein selecting a serving cell to be camped on comprises of:
selecting at least three UARFCN cell set having a high signal frequency from the plurality of UARFCNs;
performing an IMS Centralized Service (ICS) on the first UARFCN in the cell set;
performing a BCH read on cells of the first UARFCN which are above a first SNR threshold; and
camping on the serving cell of the first UARFCN if the BCH read is success.

5. The method of claim 3, further comprising:
checking if ICS is pending for any UARFCN in the cell set if the BCH read is not successful;
performing ICS on the UARFCN if UARFCN is left in the set; and
performing the BCH read on the serving cells of the UARFCN which are above the first SNR threshold.

6. The method of claim 3, further comprising:
sorting the plurality of serving cells across one or more UARFCNs of the set if no UARFCNs are present in the set for ICS;
performing the BCH read on one or more serving cells having a carrier frequency above a second SNR threshold; and
identifying the serving cell for camping on if the BCH read is success.

7. The method of claim3, further comprising:
checking if any UARFCN is left in the list, if the BCH read is not success;
selecting a next set of three UARFCNS for identifying the camp on cell if any UARFCN is left in the list; and
performing a full band frequency search if no ARFCNs is left in the list.

8. The method of claim 1, wherein a carrier frequency search is performed to identify the ordered list of UARFCNs and the SyncDL correlation energies.