TWI566614B - Method of performing cell reselection in wireless communication system - Google Patents

Description

Method for performing base station reselection in a wireless communication system

The present invention relates to a method for performing base station reselection in a wireless communication system, and more particularly to a method for performing base station reselection in a wireless communication system when the service base station is blocked.

The 3rd Generation (3G) network system developed by the 3rd Generation Partnership Project (3GPP) includes the universal mobile telecommunications system (UMTS) and the global mobile communication system. The global system for mobile communications edge radio access network (GERAN) is characterized by providing high spectrum utilization efficiency, high coverage, high quality and high rate of multimedia data transmission. The universal terrestrial radio access network (UTRAN) in the universal mobile telecommunication system can be regarded as a wireless access network, in which the network side includes a plurality of base stations (Node-B, NB), To communicate with a plurality of user equipment (UE) at the user end. In addition, in order to improve the general mobile telecommunications system, 3GPP further develops a 4th Generation (4G) long term evolution (LTE) system to meet the increasing demands of users. The Long Term Evolution (LTE) system is considered to provide a new wireless interface and wireless network architecture that provides high data transfer rates, low latency, packet optimization, and improved system capacity and coverage, including a number of evolved base stations (evolved Nodes). -B, eNB) is an evolved universal terrestrial radio access network (E-UTRAN), which is used to communicate with the UE on the one hand, and to handle non-processing on the other hand. Core network controlled by non-access stratum (NAS) The network, CN) communicates, and the core network includes devices such as a servo gateway and a mobility management entity (MME).

In accordance with the 3GPP specifications, a public land mobile network is selected. After the network identity (PLMN), the user device can perform a base cell selection procedure and a cell reselection procedure to use the associated network service. The purpose of the base station selection procedure is to allow the user equipment to quickly camp on a serving cell, thereby receiving system information from the PLMN, establishing radio resource control (RRC) connections, Access the network through the control channel, and receive/reply paging messages. The purpose of the base station reselection procedure is to allow the user device to switch to a target cell that is better camped on other signals.

After completing the base station selection procedure, the user device can continuously receive system information from the service base station, thereby knowing the cell reselection criteria, the frequency/radio access technology (RAT) list, and Status information, which in turn evaluates whether there is a target base station with a relatively good signal. Whether the base station reselection procedure needs to be performed can be based on the evaluation of intra-frequency reselection and inter-frequency reselection, and the two use different parameters as the base station reselection criteria. . The same-frequency base station re-election evaluation uses the base station signal strength as the criterion for judging. If the relative strength of the same-frequency target base station can continue to be greater than the service base station signal exceeds a reselection criterion maintenance time (Treselection _RAT ), the user device A base station re-selection procedure will be performed to relocate to the target base station.

Each frequency/RAT in the frequency list has its priority weight, and its frequency base station reselection evaluation needs to use both the base station signal strength and the reselection priority as the criterion. When the priority of the frequency is high, the user equipment performs the base station reselection process to rotate once the target base station signal strength of the frequency is maintained above a first threshold exceeding the reselection criterion maintaining time Treselection _RAT . And reside in this target base station. When the frequency priority is the same, the behavior of the user device is the same as the same frequency base station reselection process. When the priority of the frequency is low, once the target base station signal strength of the frequency is maintained above a second threshold exceeding the reselection criterion maintaining time Treselection _RAT , and the signal strength of the serving base station remains below one When the triple threshold exceeds the reselection criteria hold time Treselection _RAT , the user device performs a base station reselection procedure to camp on the target base station instead.

Related 3GPP specifications (eg TS 36.304) define different types of base stations, such as suitable base cells, acceptable base cells, barred cells, and Retained reserved cells, etc. The user device can know the type of the base station through the status information in the system information block type 3 (SIB3) or the system information block type 4 (SIB4), which is blocked. The base station and the reserved base station prohibit any user equipment from camping on it, so the base station selection procedure and the base station reselection procedure can only be performed for the appropriate base station and the acceptable base station. However, although the serving base station previously selected by the user equipment in the base station selection procedure may be allowed to perform the base station selection/base station reselection procedure, while the user equipment resides in the serving base station, the network may The base station will be set to prohibit base station selection/base station reselection for specific reasons. Thereafter, other user devices will not be able to reside on the service base station other than the base station currently camping on. Since the service base station is prohibited from performing base station selection/base station reselection and does not affect the signal strength, when other frequencies with low priority are detected, even if the target base station signal strength is higher than the second If the threshold exceeds the reselection criterion maintenance time Treselection _RAT , the signal strength of the serving base station may be maintained above the third threshold, so that the user equipment cannot perform the base station reselection process to camp on other suitable target base stations. Or accept the target base station, which will affect the communication quality.

The present invention provides a method of performing a base station reselection in a wireless communication system, the wireless communication system including a user device and a plurality of base stations. The method includes the user equipment camping on a first base station of the plurality of base stations; determining that the first base station is not prohibited from performing a base station selection or the base station weight while camping on the first base station Selecting, the user device evaluating whether a second base station in the plurality of base stations meets a first base station reselection criterion; and determining that the first base station is prohibited during the staying in the first base station When the base station selects or the base station reselects, the user equipment evaluates whether a third base station in the plurality of base stations conforms to a second base station reselection criterion. The first base station reselection criterion includes at least one first condition for determining whether the second base station conforms to the first base station reselection criterion, and the second base station reselection criterion includes at least one second condition The method is used to determine whether the third base station meets the second base station reselection criterion, and the at least one first condition is looser than the at least one second condition.

110~180‧‧‧Steps

FIG. 1 is a flow chart of a method for performing base station reselection in a wireless communication system according to an embodiment of the present invention.

For a wireless communication system including a user device and a plurality of base stations, the present invention can provide a method of performing base station reselection. Each base station can be one NB in a UTRAN, one eNB in an EUTRAN, or a base station in other types of networks. The user device may include a mobile phone, a personal digital assistant (PDA), a handheld computer, a tablet computer, a nettop computer, a laptop computer, or other wireless device. Device for communication function. However, the types of base stations and user devices do not limit the scope of the present invention.

1 is a flow chart of a method for performing base station reselection in a wireless communication system according to an embodiment of the present invention, which includes the following steps.

Step 110: The user equipment executes a base station selection procedure to select a first base station as a service base station; and step 120 is performed.

Step 120: The user equipment resides at the service base station and receives system information from the service base station; and step 130 is performed.

Step 130: The user device provides a first base station reselection criterion according to the system information; and step 140 is performed.

Step 140: The user device determines, according to the system information, whether the serving base station is prohibited from performing base station selection or base station reselection; if yes, executing step 160; if not, executing step 150.

Step 150: The user equipment evaluates whether a second base station complies with the first base station reselection criterion; if yes, step 180 is performed; if not, step 120 is performed.

Step 160: The user equipment lowers the first base station reselection criterion to provide a corresponding one of the second base station reselection criteria; and step 170 is performed.

Step 170: The user equipment evaluates whether a second base station complies with the second base station reselection criterion; if yes, step 180 is performed; if not, step 170 is performed.

Step 180: The user equipment performs a base station reselection procedure to select the second base station as the service base station; and step 120 is performed.

According to the relevant 3GPP specifications (eg TS 36.304), the base station selection procedure consists of two phases: the selected target base station and the selected service base station. In the first phase of the selected target base station, the user device selects the target base station based on the PLMN identification list owned by the user, the base station information of the memory, or the scanned list of neighboring base stations. If the base station that matches the PLMN identification list owned by the user is not found, or if no smart card is inserted, the user device selects the target base station according to the strength of the signal. After the target base station is selected, the user device begins to receive and process system information received from the target base station. The system information includes _{Q rxlevmeas, Q qualmeas, Q rxlevmin} , Q qualmin, Q rxlevminoffset, Q qualminoffset and P _compensation parameters and threshold _{Thresh Serving, LowQ, Thresh Serving,} LowP, Thresh X, LowQ and Thresh _{X, LowQ} the like, using The device can calculate parameters such as Srxlev and Squal and learn the relevant cell selection criteria/cell reselection criteria. Srxlev represents a base station selecting a cell selection RX level value, and Squal represents a cell selection quality value. Q _rxlevmeas represents a measured cell RX level value or a reference signal receiving power (RSRP). Q _qualmeas represents a measured cell quality value or a reference signal receiving quality (RSRQ). Q _rxlevmin represents a minimum required RX level in the cell. Q _qualmin represents a minimum required quality level in the cell. Q _{rxlevminoffset} represents one of the offset values included in the Srxlev evaluation when searching for higher priority PLMNs. Q _{qualminoffset} represents one of the offset values included in the Squal evaluation when searching for higher priority PLMNs. P _compensation is (P _{EMAX -} P _PowerClass ) and the larger of 0, where P _EMAX represents the maximum transmit power available to the user device and P _PowerClass represents the maximum RF output power of the user device. Thresh _{Serving, LowQ} and Thresh _{Serving, LowP} represent the low threshold used in the service frequency in the re-election evaluation. Thresh _{X, LowQ} and Thresh _{X, LowP} represent the critical values used when re-electing lower priority rates.

The units of Srxlev and Squal are decibels (dB), which are defined by the following formulas (1) and (2), respectively.

Srxlev = Q _rxlevmeas - (Q _rxlevmin + Q _{rxlevminoffset} ) - P _compensation ... (1).

Squal=Q _qualmeas -(Q _qualmin +Q _{qualminoffset} )...(2).

In the second phase of the selected service base station, the user equipment determines whether the target base station is a suitable base station based on the base station selection criteria learned from the system information provided by the target base station. The base station selection criterion is determined by using the signal receiving threshold (such as Srxlev and/or Squal) and status information indicated in the target base station system information. Equation (3) shows the base station selection criterion S1 under the frequency division duplex (FDD) architecture. Equation (4) shows the base station selection criteria under the time division duplex (TDD) architecture. S2.

S1: Srxlev>0 and Squal>0...(3).

S2: Srxlev>0...(4).

In step 110, if the first base station is selected in the first phase, it is determined in the second phase that the signal strength of the first base station is greater than the signal reception threshold (eg, satisfies the base station selection criterion S1 or S2), and the first base The status information of the station indicates that the base station selection or base station reselection is not prohibited. At this time, the user equipment selects the first base station as the service base station.

In step 120, the user device resides at the serving base station and continuously receives system information from the service base station, thereby learning the base station reselection criteria, frequency list, and status information to perform re-selection of the base station evaluation accordingly.

The relevant 3GPP specifications (e.g., TS 36.304) define base station reselection criteria, and equations (5) to (7) show base station reselection criteria R1 to R3 for low priority frequencies in different architectures. All conditions in each base station reselection criteria need to be established beyond the reselection criteria maintenance time Treselection _RAT to be considered as meeting the base station reselection criteria.

R1: Squal<Thresh _{Serving, LowQ of the} service base station; and Squal>Thresh _{X, LowQ} ... (5) of the target base station.

R2: Squal<Thresh _{Serving, LowQ of the} service base station; and Srxlev>Thresh _{X, LowP} ... (6) of the target base station.

R3: Srxlev<Thresh _{Serving, LowP of the} service base station; and Srxlev>Thresh _{X, LowP} ... (7) of the target base station.

In step 130, the first base station reselection criterion provided by the user equipment may be one of the base station reselection criteria R1 R R3. If the critical value Thresh _{Serving, LowQ} can be received from the SIB3 broadcast by the serving base station, the user equipment will use the base station reselection criterion R1 to perform base station reselection evaluation on the RAT/frequency of the lower priority EUTRAN or UTRAN FDD. Or use the base station reselection criteria R2 for the lower priority UTRAN TDD, Global System for Mobile Communications Enhanced Data rates for GSM Evolution Radio Access Network (Global System for Mobile Communications Enhanced Data Rates for GSM Evolution Radio Access Network, Base station reselection evaluation is performed by GERAN), or RAT/frequency of Code Division Multiple Access (CDMA) 200. If the critical value Thresh _{Serving, LowQ is not} received from the SIB3 broadcast by the serving base station, the user equipment will use the base station reselection criterion R3 to perform base station reselection evaluation on the lower priority RAT/frequency. However, the implementation of the first base station reselection criteria does not limit the scope of the invention.

As previously mentioned, although the user device may be allowed to perform base station selection/base station reselection at the first base station previously selected as the serving base station in step 110, but when the user device resides at the serving base station During this period, the network may change the status information of the first base station for specific reasons. For example, the status information in the SIB3 or SIB4 broadcast by the first base station includes "being Information box (Cell barred), "Cell reserved for operator use", and "Cell reservation on extension" and other information elements (IE). When the network allows the first base station to operate normally, the information element can be set to an "not barred" state; when the network side does not want any user device to reside on the first base station, the above information element Can be set to "barred" status.

In step 140, if the user device determines, according to the system information, that the serving base station is not prohibited from performing base station selection or base station reselection, then in step 150, it is evaluated whether the second base station is eligible for the first base station reselection. The criteria, and in accordance with the first base station reselection criteria, performs a base station reselection operation in step 180 to select the second base station as the service base station. Once the user device determines, according to the system information, that the service base station is prohibited from performing base station selection or base station reselection, step 160 is performed.

In step 160, the user device may lower the first base station reselection criteria for low priority frequencies to provide a second base station reselection criterion. In an embodiment of the present invention, the second base station reselection criterion provided in step 160 may be one of the following base station reselection criteria A1~A3, as shown in equations (8)-(10). All conditions in each base station reselection criteria need to be established beyond the reselection criteria maintenance time Treselection _RAT to be considered as meeting the base station reselection criteria.

A1: Squal>Thresh _{X, LowQ} ... (8) of the target base station.

A2: Srxlev>Thresh _{X, LowP} ... (9) of the target base station.

A3: Srxlev>Thresh _{X, LowP} ... (10) of the target base station.

In another embodiment of the present invention, the second base station reselection criterion provided in step 160 may be one of the following base station reselection criteria B1 to B3, as shown in equations (11)-(13). All conditions in each base station reselection criteria need to be established beyond the reselection criteria maintenance time Treselection _RAT to be considered as meeting the base station reselection criteria.

B1: Squal <MAX1 of the service base station; and Squal>Thresh _{X, LowQ} ... (11) of the target base station.

B2: Squal<MAX1 of the service base station; and Srxlev>Thresh _{X, LowP} ... (12) of the target base station.

B3: Srxlev<MAX2 of the service base station; and Srxlev>Thresh _{X, LowP} ... (13) of the target base station.

If it is determined in step 140 that the serving base station is prohibited from performing base station selection or base station reselection, the user device evaluates in step 170 whether the second base station complies with the second base station reselection criteria. If the second base station reselection criterion is one of the base station reselection criteria A1~A3, the reselection evaluation for the lower priority RAT/frequency will ignore the Squal or Srxlev of the service base station. In other words, compared with the conditions for judging whether it meets the criteria of the base station re-election criteria R1 to R3, it is more relaxed to determine whether the conditions for the base station re-election criteria A1 to A3 are met. Therefore, even if the Squal of the blocked service base station is greater than Thresh _{Serving, the LowQ} or the blocked service base station Srxlev is larger than the Thresh _{serving, LowP} , as long as the second base station satisfies Squal>Thresh _{X, LowQ} or Srxlev>Thresh _{X, LowP} , The user device performs a base station reselection operation in step 180 to select the second base station as the serving base station.

If the second base station reselection criterion is one of the base station reselection criteria B1 to B3, the re-election evaluation for the lower priority RAT/frequency uses the threshold MAX1 or MAX2, where MAX1>Thresh _{X, LowQ} and MAX2>Thresh _{X, LowP} . In other words, compared with the conditions for judging whether it meets the criteria of the base station re-election criteria R1 to R3, it is more relaxed to determine whether the conditions for the base station re-election criteria B1 to B3 are met. Therefore, when the second base station satisfies Squal>Thresh _{X, LowQ} or Srxlev>Thresh _{X, LowP} , the signal of the serving base station is more likely to satisfy Squal<MAX1 or Srxlev<MAX2, so that the user device can execute in step 180. The base station re-election operation selects the second base station as the service base station.

In the method for performing base station reselection according to the present invention, when the user equipment resides in the service base station, if the network side sets the service base station to prohibit base station selection/base station reselection for a specific reason, The user device will use a looser base station reselection criteria to assess whether a base station reselection procedure is required. Therefore, the present invention can make the user device residing on the blocked base station easier to relocate to another suitable target base station or an acceptable target base station, thereby improving communication quality.

The above are only the preferred embodiments of the present invention, and all changes and modifications made to the scope of the present invention should be within the scope of the present invention.

110~180‧‧‧Steps

Claims (9)

A method of performing a cell reselection in a wireless communication system, the wireless communication system including a user device and a plurality of base stations, the method comprising: camping on the user device a first base station of the plurality of base stations; the user is determined to be in the first base station while the first base station is not prohibited from performing a cell selection or the base station reselection The device evaluates whether a second base station in the plurality of base stations conforms to a first base station reselection criterion; and determines that the first base station is prohibited from performing the base station selection or the base during the period of camping on the first base station When the station is reselected, the user equipment evaluates whether a third base station in the plurality of base stations meets a second base station reselection criterion, wherein: the first base station reselection criterion includes at least one first condition for determining Whether the second base station complies with the first base station reselection criterion; the second base station reselection criterion includes at least one second condition for determining whether the third base station is in conformity The second base station reselection criterion; and the at least one second condition is looser than the at least one first condition. The method of claim 1, further comprising: receiving, during the camping of the first base station, the user device receives system information from the first base station; the user device is in accordance with the status indicated by the system information Information to determine whether the first base station is prohibited from performing the base station selection or the base station reselection. The method of claim 2, wherein the status information comprises a "Cell Barred" information as defined in the 3rd Generation Partnership Project (3GPP) specification. An information element (IE), a "Cello reserved for operator use" information element, and an "Cell reservation on extension" information element; The user device is blocked when the information element of the "base station" information element, the "base station reserved for the operator" information element and the "base station" information element of the "extended retention" are set to a "barred" state. Determining that the first base station is prohibited from performing the base station selection or the base station reselection; and when the "blocked base station" information component, the "base station reserved for the operator" information element, and the "extension retention" When the base station information element is set to an "not barred" state, the user device determines that the first base station is not prohibited from performing the base station selection or the base station reselection. The method of claim 1, comprising: receiving, during the first base station, the system information from the first base station comprising a plurality of parameters and a plurality of threshold values; and the using And determining, according to the plurality of parameters, a first cell selection quality value (Squal) related to the first base station, a second Squal related to the second base station, and related to a third Squal of the third base station; wherein the plurality of parameters include a measured cell quality value (Q _qualmeas ) and a minimum required quality level in a base station (minimum required quality level in The cell, Q _qualmin ), and one of the offsets (Q _{qualminoffset} ) included in a Squal assessment associated with searching for a higher priority public land mobile network identity (PLMN); When the Squal is less than a first threshold and the second Squal is greater than a second threshold for more than a predetermined time, the user equipment determines that the second base station meets the first base station reselection ; Squal and when the third value is greater than the second threshold exceeds the predetermined time, the user device determines the third base station in line with the second base station reselection criterion. The method of claim 1, comprising: receiving, during the first base station, the system information from the first base station comprising a plurality of parameters and a plurality of threshold values; and the using And determining, according to the plurality of parameters, a first cell selection quality value (Squal) related to the first base station, a second Squal related to the second base station, and related to a third Squal of the third base station; wherein the plurality of parameters include a measured cell quality value (Q _qualmeas ) and a minimum required quality level in a base station (minimum required quality level in The cell, Q _qualmin ), and one of the offsets (Q _{qualminoffset} ) included in a Squal assessment associated with searching for a higher priority public land mobile network identity (PLMN); When the Squal is less than a first threshold and the second Squal is greater than a second threshold for more than a predetermined time, the user equipment determines that the second base station meets the first base station reselection When the first Squal is less than a third threshold and the third Squal is greater than the second threshold exceeds the predetermined time, the user equipment determines that the third base station meets the second base station reselection criterion; The third critical value is greater than the second critical value. The method of claim 1, comprising: receiving, during the first base station, the system information from the first base station comprising a plurality of parameters and a plurality of threshold values; and the using The device determines, according to the plurality of parameters, a cell selection quality value (Squal) related to the first base station, and a first base station selects a receiving level value corresponding to the second base station. (cell selection RX level value, Srxlev), and a second Srxlev associated with the third base station; wherein the plurality of parameters include a measured cell RX level value (Q _rxlevmeas ), A measured cell quality value (Q _qualmeas ), a minimum required RX level in the cell (Q _rxlevmin ), and a minimum required quality level in a base station ( _Minimum required quality level in the cell, Q _qualmin ), related to the search for a higher priority public land mobile network identity (PLMN) and included in an Srxlev assessment One of the offset values _(Q rxlevminoffset), associated with a higher priority PLMN search and included in one of an offset value of the evaluation Squal _(Q qualminoffset), a user device may use the maximum transmit power (P _EMAX) And a maximum RF output power of the user device (P _PowerClass ); when the Squal is less than a first threshold and the first Srxlev is greater than a second threshold for more than a predetermined time, the user device determines the second The base station conforms to the first base station reselection criterion; and when the second Srxlev is greater than the second threshold value for more than the predetermined time, the user equipment determines that the third base station complies with the second base station reselection criterion. The method of claim 1, comprising: receiving, during the first base station, the system information from the first base station comprising a plurality of parameters and a plurality of threshold values; and the using The device determines, according to the plurality of parameters, a cell selection quality value (Squal) related to the first base station, and a first base station selects a receiving level value corresponding to the second base station. (cell selection RX level value, Srxlev), and a second Srxlev associated with the third base station; wherein the plurality of parameters include a measured cell RX level value (Q _rxlevmeas ), A measured cell quality value (Q _qualmeas ), a minimum required RX level in the cell (Q _rxlevmin ), and a minimum required quality level in a base station ( minimum required quality level in the cell, Q qualmin), related to the search for higher priority public land mobile network (public land mobile network identity, PLMN ) and included a comment in Srxlev One of the offset values _(Q rxlevminoffset), associated with a higher priority PLMN search and included in one of an offset value of the evaluation Squal _(Q qualminoffset), a user device may use the maximum transmit power (P _EMAX) And a maximum RF output power of the user device (P _PowerClass ); when the Squal is less than a first threshold and the first Srxlev is greater than a second threshold for more than a predetermined time, the user device determines the second The base station meets the first base station reselection criterion; when the Squal is less than a third threshold and the second Srxlev is greater than the second threshold exceeds the predetermined time, the user equipment determines that the third base station meets the a second base station reselection criterion; and the third threshold value is greater than the second threshold value. The method of claim 1, comprising: receiving, during the first base station, the system information from the first base station comprising a plurality of parameters and a plurality of threshold values; and the using The device determines, according to the plurality of parameters, a cell selection RX level value (Srxlev) related to one of the first base stations, and a second Srxlev associated with the second base station. And a third Srxlev related to the third base station; wherein the plurality of parameters include a measured cell RX level value (Q _rxlevmeas ) and a minimum required receiving level in a base station ( _Minimum required RX level in the cell, Q _rxlevmin ), related to searching for a higher priority public land mobile network identity (PLMN) and including one of the Srxlev evaluations (Q _{rxlevminoffset} ), the user device may use a maximum transmit power (P _EMAX), and a maximum RF output power of the user apparatus (P _PowerClass); Srxlev when the first value is less than a first threshold and the When the second Srxlev is greater than a second threshold for more than a predetermined time, the user equipment determines that the second base station meets the first base station reselection criterion; and when the third Srxlev is greater than the second threshold value exceeds the predetermined time The user device determines that the third base station complies with the second base station reselection criteria. The method of claim 1, comprising: receiving, during the first base station, the system information from the first base station comprising a plurality of parameters and a plurality of threshold values; and the using The device determines, according to the plurality of parameters, a cell selection RX level value (Srxlev) related to one of the first base stations, and a second Srxlev associated with the second base station. And a third Srxlev related to the third base station; wherein the plurality of parameters include a measured cell RX level value (Q _rxlevmeas ) and a minimum required receiving level in a base station ( _Minimum required RX level in the cell, Q _rxlevmin ), related to searching for a higher priority public land mobile network identity (PLMN) and including one of the Srxlev evaluations (Q _{rxlevminoffset} ), the user device may use a maximum transmit power (P _EMAX), and a maximum RF output power of the user apparatus (P _PowerClass); Srxlev when the first value is less than a first threshold and the When the second Srxlev is greater than a second threshold for more than a predetermined time, the user equipment determines that the second base station meets the first base station reselection criterion; and when the first Srxlev is less than a third threshold and the third When the Srxlev is greater than the second threshold exceeds the predetermined time, the user equipment determines that the third base station meets the second base station reselection criterion; and the third threshold is greater than the second threshold.