RU2450488C1 - Method to select cell in hierarchical cellular structure based on cell quality - Google Patents

Abstract

FIELD: information technologies.

SUBSTANCE: if a hierarchical cellular structure (HCS) is used in a service cell of UE, a ranging procedure is performed by the first method, if UE has low mobility, and the ranging procedure is performed by the second method, if UE has high mobility. When UE has low mobility, the ranging procedure is performed for all measured cells, which have the highest HCS-priority from those cells, which comply with the criterion S and the criterion H>=0, or the ranging procedure is performed for all measured cells independently on HCS-priorities, if neither cell does not comply with the criterion S and the criterion H>=0. When UE has high mobility, the ranging procedure is performed for all measured cells, and if there are cells with a lower HCS-priority compared to the service cell, which corresponds to the criterion S and the criterion H>=0, the ranging procedure is performed for all cells with the highest HCS-priority. Otherwise if there are cells complying with the criterion S and the criterion H>=0 with the HCS-priority, which exceeds or is equal to the HCS-priority of the service cell, then the ranging procedure is performed for all cells having the least HCS-priority, otherwise, the ranging procedure is performed for all cells independently on HCS-priorities.

EFFECT: higher efficiency of using radio resources.

14 cl, 7 dwg

Description

Technical field

The present invention relates to a method for selecting a cell in a hierarchical cellular structure based on cell quality.

State of the art

In the prior art, cell selection is performed, but radio resources are wasted. In fact, prior art technologies do not adequately solve these problems and thus do not offer appropriate solutions.

SUMMARY OF THE INVENTION

Technical solution

The inventors of the present invention have identified at least the aforementioned drawbacks of the prior art as a result of testing for non-service conditions. Based on this identification, the various features described below are considered such that a method for selecting a cell in a hierarchical cellular structure based on cell quality is provided, which leads to more efficient use of radio resources.

Brief Description of the Drawings

Figure 1 shows an exemplary network architecture of a universal mobile communications system (UMTS).

2 shows an exemplary radio protocol stack used in UMTS.

Figure 3 shows exemplary equations that specify the conditions used by the mobile terminal to select a cell having a signal strength and quality that exceeds specific values set by the system.

4 shows a flowchart of an example method for selecting (reselecting) a cell in WCDMA.

5 shows equations for calculating criterion R values used by a mobile terminal for a cell ranking process.

6 shows the principle of an exemplary hierarchical cell structure (HCS).

7 shows exemplary procedures for calculating the values of criterion H.

An embodiment of the invention

The principles and features of the invention in this document related to the method of selecting a cell in a hierarchical cellular structure based on cell quality are explained in terms of a long-term development (LTE) system or other so-called 4G communication systems, which are an improvement in current 3GPP- technologies. However, such details are not intended to limit the various features described herein that are applicable to other types of mobile and / or wireless communication systems and methods.

Further, the term “mobile terminal” is used to refer to various types of user devices, such as mobile communication terminals, subscriber units (UEs), mobile devices (MEs), and other devices that support various types of wireless communication technologies.

In mobile communications, cell selection is the process by which a mobile terminal searches for a suitable cell (candidate). When a cell is selected as a result of cell selection, the selected cell is called a fixed cell. When securing in a cell, the mobile terminal should regularly search for a more optimal cell according to various criteria for cell reselection (explained below), and if a more optimal cell is detected, this more optimal cell is selected.

As a rule, large cells (for example, macro cells) cannot support a large number of users, but they can support users moving at high speed. As a rule, small cells (for example, microcells or picocells) can support a large number of users, but cannot support users moving at high speed. These problems can be solved using a hierarchical cellular structure (HCS), which defines a certain number of overlapping cells of various sizes, which form several levels of cells. This type of cellular structure enables the network to efficiently use the geographic area and serve a larger number of users.

To specify at what HCS cell level the UE should be, an HCS priority (HCS_PRIO) is set. Such priority information may be transmitted as part of the broadcast information in the cell (for example, SIB 11 and SIB 12 for neighboring cells and SIB 13 and SIB 14 for serving cells). For neighboring cells, such priority information may also be transmitted as part of the RRC measurement control message. HCS cells can be assigned priorities from 0-7, where 0 is the lowest priority and 7 is the highest priority. Cells near the serving cell may be given the highest priority.

Cell reselection criteria may include criterion H (i.e., the HCS criterion used when HCS is used, which is a positive or negative value calculated based on information sent in system information and measurements from CPICH / P-CPCCH cell), criterion S (i.e., a selection or eligibility criterion used to check whether or not the reception quality of the candidate cell is sufficient) and criterion R (i.e., the ranking criterion used by the mobile terminal to to rank the list with from satisfying criterion S).

The present invention is intended to improve cell selection (reselection) procedures so that the occurrence of out-of-service states is reduced. The so-called out-of-service states mean that the mobile terminal cannot receive a specific service from the mobile network for various reasons. In order to resolve the state of being out of service, the mobile terminal must perform a full cell search procedure that consumes battery power and causes delays that the user may notice.

The procedures for selecting (reselecting) a cell use various conditions, including criterion H and criterion S. The present inventors have found that the procedure for selecting (re-selecting) cells of the prior art has several drawbacks. This is because since the prior art mainly considers criterion H and then further considers criterion S as a secondary condition or even ignores criterion S. Based on this identification of a problem, the present invention gives greater emphasis and significance to criterion S than to criterion H resulting in improved cell selection and reselection.

The present invention relates to a method for selecting a cell from which a mobile terminal receives a service in UMTS (universal mobile communication system), which is a European IMT-2000 system. In particular, the present invention relates to a method for a mobile terminal to take into account the quality of each of a plurality of cells when selecting a particular cell in which a service is to be received.

Figure 1 shows the network architecture of a universal mobile communication system (UMTS) 100. A UMTS system mainly consists of a subscriber unit (UE) 130, a UMTS terrestrial radio access network (UTRAN) 120, and a core network (CN) 110. UTRAN 120 has one or more radio network subsystems (RNS) 122, and each RNS has a radio network controller (RNC) 124 and one or more nodes B 126 that are administered by the RNC 124. One or more cells 128 exist for node B.

Figure 2 shows the radio protocol stack used in UMTS. The radio protocol layers exist in pairs in the mobile terminal and in the UTRAN and process the data transmission over the radio interface. This radio communication protocol stack is broadly divided into three levels: L1 (level 1), L2 (level 2) and L3 (level 3).

L1 (Level 1) has a Physical Layer (PHY) that uses various types of radio technology to reliably transmit data over the air. The PHY layer is connected to the upper layer (MAC layer) through transport channels, which can be divided into dedicated transport channels and common transport channels.

L2 (level 2) consists of four sublayers: MAC, RLC, PDCP and BMC, each of which is described in more detail below.

The MAC (Media Access Control) layer converts various logical channels into different transport channels, and also multiplexes logical channels for several logical channels into one transport channel. The MAC layer connects to the upper layer (RLC layer) through one or more logical channels. Based on the type of information that is transmitted, these logical channels can be divided into control channels used to transmit information to the control plane and traffic channels used to transmit information to the user plane. Based on the types of transport channels that are being administered, the MAC layer can be divided into a MAC-b sublayer, a MAC-c / sh sublayer, a MAC-d sublayer, a MAC-hs sublayer, and a MAC-e sublayer. The MAC-b sublayer handles the administration of the BCH (broadcast channel) used to broadcast system information. The MAC-c / sh sublayer administers shared transport channels, such as FACH (direct access channel), DSCH (downlink shared channel) and the like, which are shared with other mobile terminals. The MAC-d sublayer processes administration by dedicated transport channels, such as DCH (Downlink Shared Channel), with respect to a particular mobile terminal. To support high speed downlink and uplink data transmissions, the MAC-hs sublayer administers the HS-DSCH (High Speed Downlink Shared Channel), which is a transport channel for high speed downlink data. The MAC-e sublayer administers an E-DCH (Advanced Dedicated Channel), which is a transport channel for high speed uplink data transmissions.

The RLC (Radio Control) layer processes the Quality of Service (QoS) guarantee of each unidirectional radio channel (RB) and data transmission thereon. For RLCs, in order to guarantee QoS that is unique to RBs, one or two independent RLCs exist for each RB and three types of RLC modes (TM: transparent mode; UM: non-acknowledged mode; AM: acknowledged mode) Provided to support various QoS. In addition, the RLC adjusts the size of the data so as to correspond to the transmission over the air interface through the lower level, and performs the functions for segmenting and combining data received from the upper level.

The PDCP (Packet Convergence Protocol) layer is located above the RLC layer and enables the transmission of data using IP packets (such as IPv4 or IPv6) over the air interface having a relatively small bandwidth in an efficient manner. For this, the PDCP layer performs the function of header compression, which enables the transmission of data that is necessary only in part of the data header, so that the transmission efficiency over the air interface is improved. The PDCP layer exists only in the PS domain (packet switched), since header compression is a basic function, and one PDCP entity exists per RB to effectively provide header compression functions with respect to each PS service.

The BMC (Broadcast / Multicast Control) layer exists above the RLC layer and performs functions related to scheduling broadcast messages in a cell and broadcasting to mobile terminals located in a particular cell.

L3 (level 3) has an RRC (radio resource control) level located at the very bottom, which is set only in the control plane, for controlling the parameters L1 and L2 regarding the establishment, re-establishment and release of unidirectional radio channels, as well as control of logical channels, transport channels and physical channels. Here, a unidirectional radio channel is referred to as a logical path, which is provided through L1 and L2 of a radio communication protocol for transmitting data between a mobile terminal and a UTRAN. In general, the establishment of a unidirectional radio channel is referred to as a procedure for specifying the characteristics of the levels of radio communication protocols and channels necessary to provide specific services, and then setting each specific parameters and working methods for them.

The procedure for selecting a cell by the mobile terminal in the standby mode is explained in more detail.

Basically, the reason for choosing a cell is to register on the network in order to receive service from the base station. Here, if the intensity or quality of the signals between the mobile terminal and the base station decreases due to the mobility of the mobile terminal in order to maintain data transmission quality, the mobile terminal re-selects another cell. Further, characteristics of physical signals, such as signal strength and interference-to-noise ratio, are simply referred to as signal characteristics.

As described above, a method for selecting a cell based on signal characteristics according to a radio environment is provided. The mobile terminal may also need to use the cell selection procedure based on the following reasons: UE characteristics, subscriber information, load balancing by pin, load balancing by traffic, etc.

The following describes a method and procedures for selecting a cell in WCDMA.

When the mobile terminal is turned on for the first time (or supplied with power), PLMN and RAT are selected for radio communication, and the mobile terminal performs signal measurement procedures using the base station in all searchable frequency bands, and then the cell having the strongest signal characteristics value is selected from cells that satisfy the conditions of FIG. 3, and is accessed. In the CPICH WSCMA system, RSCP, CPHIC Ec / N0 and Carrier RSSI are used as values for the above signal measurement procedures.

In FIG. 3, it can be seen that the mobile terminal selects a cell having a signal strength and quality that exceeds the specific values set by the system (intensity: Qrxlevmin + Pcompensation, quality: Qqualmin). Here, these values (Qrxlevmin, Pcompensation, quality: Qqualmin) are reported from the base station to the mobile terminal via system information (SI). In addition, the mobile terminal waits in standby mode to request a service for the network (for example, to make an outgoing call) or to receive a service from the network (such as an incoming call). In standby mode, the mobile terminal measures the signals of the cell from which it is currently receiving a service, and signals from neighboring cells and repeats the procedures for reselecting cells that have better signal characteristics.

4 shows a flowchart of an example method for selecting (reselecting) a cell in WCDMA. In standby mode, the mobile terminal periodically performs a measurement procedure with respect to the values (Rs) of the signal characteristics of the cell from which the service is received and the values (Rn) of the signal characteristics of neighboring cells from cells that satisfy the conditions of FIG. 3, as shown in step S401. If the condition Rn> Rs is satisfied for a specific time (Treselection), the intensities and signal quality of the cells corresponding to Rn are compared using a ranking procedure or process, as shown in step S403. As a result, a cell having the highest (or largest) characteristic value is selected, as shown in step S405. Namely, another cell is selected that has the best signal characteristics compared to the cell from which the service is currently being received.

The values of Rs and Rn are obtained using the equations in FIG. 5. Treselection is the value that the base station reports to the mobile terminal via system information (SI), and is used to prevent re-selection of a particular cell by applying such a restriction that cell selection conditions must be satisfied for a period exceeding a certain amount of time.

5 shows equations for calculating criterion R values used by a mobile terminal for a cell ranking process. Here, Rs represents the ranking of serving cells, and Rn represents the ranking of neighboring cells. Q _meas , _s denotes a CPICH Ec / N0 value measured relative to the cell from which the service is received, and Q _{meas, n} denotes a CPICH Ec / N0 value measured in a mobile terminal relative to neighboring cells. The value of Q _{hysts is} used for the mobile terminal to apply a weighted value relative to the currently received service, while the value of Q _{offsets, 0 is} used to reduce the offset between the cell that is currently being accessed and the cell that must be accessed , or the Q value _{offmbms is} used to apply a weighted value with respect to a cell that supports point-to-multipoint services (such as MBMS).

Similar to the WCDMA cell selection method, the cell selection method based on the signal characteristics enables the mobile terminal to select a cell with good signal reception characteristics for receiving services from the base station so that the signals sent by the transmitter can be interpreted by the receiver with minimal errors. Regarding the cells that can be selected, criterion R values are obtained, and then the ranking is performed so that the cell having the best signal characteristics is selected (or reselected) through such a ranking process.

However, in WCDMA, if a hierarchical cell structure (HCS) function is needed, it can be used.

6 shows an example of a cellular structure for HCS. Namely, several cells can exist in one region (or zone), due to which the diameter (or other sizes) of each cell are different. 6, the frequencies O, N, and M may be identical or different, and just one example is illustrated. In addition, in FIG. 6, cells having priority C are cells that have the largest diameter, while cells having priority A have the lowest priority.

HCS, as described in FIG. 6, can be used, for example, to reduce changes due to movement of a mobile terminal at different speeds between cells. For example, suppose there is a mobile terminal A and a mobile terminal B moving from right to left in FIG. 6, wherein the mobile terminal A moves at 5 km / h and the mobile terminal B moves at 50 km / h. If these two mobile terminals select cells with priority A, it can be understood that mobile terminal B should change cells 10 times more often than mobile terminal A within a given time period. When a mobile terminal needs to frequently replace cells, power consumption and radio resources are wasted due to frequent cell updates. Thus, in such cases, the base station instructs mobile terminals having a high speed to select cells with priority C (namely, cells having a large diameter), and a mobile terminal having a low speed to select cells with priority A (namely, cells having a small diameter), which leads to more efficient operation for mobile terminals.

In these cases, when signs of HCS are used, the operation of the mobile terminal should vary. 7 shows procedures for calculating values of criterion H. Thus, when HCS is used, the cell selection procedure is as follows:

1. If the current serving cell indicates that HCS is in use, the mobile terminal determines the cells that fall under the following conditions:

a. When the mobile terminal moves at low speed:

i. Of the cells that satisfy H> = 0, all measured cells having the highest HCS_PRIO value

ii. If no cell satisfies H> = 0, all measured cells, regardless of HCS_PRIO values

b. When the mobile terminal moves at high speed:

i. Of the cells that satisfy H> = 0, when there is a cell having a lower HCS priority than the current serving cell (condition 1):

1. Of the cells having a lower HCS priority than the current serving cell, all measured cells having the highest HCS_PRIO values from the cells that satisfy H> = 0.

ii. In other cases (i.e., when condition 1 is not satisfied):

1. Of the cells having HCS priority, which is identical to or higher than the priority of the current serving cell, if any cell satisfies H> = 0 (condition 2):

a. Of cells having an HCS priority that is identical to or higher than the priority of the current serving cell, cells having the lowest HCS_PRIO value of all measured cells that satisfy H> = 0

2. In other cases (that is, when condition 2 is not satisfied)

a. All measured cells, excluding HCS priority

2. For the cells defined in the above procedure 1, from cells that satisfy the criterion S, the mobile terminal performs a ranking process based on criterion R and selects the cell (s) with the best quality, and the selection (reselection) of this cell is performed.

In the above explanation, said criterion S is used by the mobile terminal to determine whether or not the various cells satisfy the conditions of guaranteed minimum quality. Namely, criterion S is used to determine whether or not a particular cell satisfies the minimum conditions necessary when making search calls or an RRC connection.

The cell reselection procedure of the mobile terminal when the HCS is set is explained above, and according to such a procedure, there may be cases where the mobile terminal cannot select a cell in which it is possible to be fixed, and thereby cannot properly receive services. For example, the following honeycomb structure may be considered.

Honeycomb Criterion H Criterion S HCS_PRIO A Satisfied Not satisfied four B Not satisfied Satisfied four C Satisfied Satisfied 3

According to the prior art, a mobile terminal performs the following:

Step 1. Perform the necessary measurements.

Cell A, Cell B, and Cell C are measured.

Stage 2. Checking whether or not there are cells that meet the criterion H> = 0.

Cell A and cell C satisfy criterion H.

Step 3. Identification of the highest HCS_PRIO of the cells verified in step 2.

Between cell A and cell C, cell A has the highest HCS_PRIO, which is 4.

Step 4. Cell identification with HCS_PRIO identified in step 3.

Cell A is the only cell with the highest HCS_PRIO.

Step 5. Verification of cells that meet criterion S from the cells identified in step 4.

Cell A does not satisfy criterion S.

Step 6. Perform the ranking for the cells identified in step 5.

There is no candidate cell for ranking.

In the above table 1, the mobile terminal must select cell C, but in the prior art, the mobile terminal cannot select any of the cells. Namely, in the prior art, the mobile terminal first selects a cell (s) that satisfies the criterion H and selects the best cell from the cells that satisfy the criterion S. Thus, in the operation procedure according to the criterion H, if there is a cell that does not satisfy criterion S, but satisfies criterion H, there may be a problem of the mobile terminal setting an inappropriate HCS_PRIO value. In this case, the mobile terminal cannot find a cell from which the service is to be received, and a problem of inability to start or receive a call may occur.

Thus, for a system that uses the HCS function, the present invention provides a method for a mobile terminal that properly performs efficient transmission, through a PS network or a radio communication protocol that only supports a PS service, of data generated in a cell from which the provision of services must be accepted.

For this, during the procedure for selecting the cell from which the service is to be received, and in particular, when the current serving cell reports that it is using HCS, it is proposed for the mobile terminal to take into account criterion S when creating a list of selectable cells using criterion H relative to the cells, for which the mobile terminal must take measurements.

In the present invention, when criterion H is applied by a mobile terminal, the cells to which criterion H is applied are those cells that already satisfy criterion S.

In the present invention, after applying the criterion H in accordance with the present invention, if each cell satisfies the criterion H, an additional check is carried out to check whether criterion S is also satisfied or not, and the ranking process is performed for those cells that satisfy the criterion H, and criterion S.

The following is an example of the operation of the mobile terminal of the present invention. When HCS is used, the cell selection procedure is as follows:

1. With respect to the cell for which measurements are made, the mobile terminal determines which cells satisfy the criterion S. In addition, the next step 2 is performed only for these specific cells.

2. From the cells that satisfy the above step 1, namely, from the cells that satisfy the criterion S, the mobile terminal determines the cells that satisfy the following additional conditions.

a. When the mobile terminal moves at low speed:

i. Of the cells that satisfy H> = 0, all measured cells having the highest HCS_PRIO value

ii. If no cell satisfies H> = 0, all measured cells, regardless of HCS_PRIO values

b. When the mobile terminal moves at high speed:

i. Of the cells that satisfy H> = 0, when there is a cell having a lower HCS priority than the current serving cell (condition 1):

1. Of the cells having a lower HCS priority than the current serving cell, all measured cells having the highest HCS_PRIO values from the cells that satisfy H> = 0.

ii. In other cases (i.e., when condition 1 is not satisfied):

1. Of the cells having HCS priority, which is identical to or higher than the priority of the current serving cell, if any cell satisfies H> = 0 (condition 2):

a. Of cells having an HCS priority that is identical to or higher than the priority of the current serving cell, cells having the lowest HCS_PRIO value of all measured cells that satisfy H> = 0

2. In other cases (that is, when condition 2 is not satisfied)

a. All measured cells, excluding HCS priority

3. From the cells determined through step 2 above, the mobile terminal performs a ranking process according to criterion R, selects the cell having the best quality, and performs selection (reselection) of the cell in this cell.

When HCS is used, the cell selection procedure according to another embodiment of the present invention is as follows.

1. If the current serving cell reports that it uses HCS, the mobile terminal determines the cells that satisfy the following conditions:

a. When the mobile terminal moves at low speed:

i. Of the cells that satisfy H> = 0 and satisfy the criterion S, all measured cells having the highest HCS_PRIO value

ii. If no cell satisfies H> = 0, and also satisfies criterion S, all measured cells that satisfy criterion S are independent of HCS_PRIO values

b. When the mobile terminal moves at high speed:

i. Of the cells that satisfy H> = 0 and satisfy the criterion S, when there is a cell having a lower HCS priority than the current serving cell (condition 1):

1. Of the cells having a lower HCS priority than the current serving cell, all measured cells having the highest HCS_PRIO values from the cells that satisfy H> = 0 and also satisfy criterion S.

ii. In other cases (i.e., when condition 1 is not satisfied):

1. Of the cells having HCS priority, which is identical or higher than the priority of the current serving cell, if any cell satisfies H> = 0, and also satisfies the criterion S (condition 2):

a. Of cells having an HCS priority that is identical to or higher than the priority of the current serving cell, cells having the lowest HCS_PRIO value of all measured cells that satisfy H> = 0 and also satisfy criterion S

2. In other cases (that is, when condition 2 is not satisfied)

a. All measured cells that meet S criterion, excluding HCS priority

2. For the cells defined in the above step 1, the mobile terminal performs a ranking process based on criterion R and selects the cell (s) with the best quality, and the selection (reselection) of this cell is performed.

For the example shown in table 1 above, the results of the present invention can be described as follows:

Step 1. Perform the necessary measurements.

Cell A, Cell B, and Cell C are measured.

Step 2. Check whether or not there are cells that meet the criteria S.

Cell B and cell C satisfy criterion S.

Stage 3. Checking whether or not there are cells that meet the criterion H> = 0 of the cells checked in stage 2.

Between cell B and cell C, cell C satisfies criterion H.

Step 4. Identification of the highest HCS_PRIO of the cells verified in step 3.

Cell C has the highest HCS_PRIO, which is 3.

Step 5. Cell identification with HCS_PRIO identified in step 4.

Cell C is the only cell with the highest HCS_PRIO.

Step 6. Perform the ranking for the cells identified in step 5.

Cell C is a ranking candidate cell.

The results of the present invention are as follows. As described above, for a cellular structure that uses the HCS function, the mobile terminal performs cell selection, whereby criterion H and criterion S are appropriately used, so that services to the mobile terminal can be provided in a more stable and efficient way.

Some additional information about the principles and features of the present invention is explained as follows:

Details # 1

If HCS is not used in the serving cell, then the UE shall perform a ranking of all cells that meet the criterion S from:

- all measured cells

If HCS is used in a serving cell, then the UE must perform a ranking of all cells that meet the S criterion from:

1. low mobility

- all measured cells that have the highest HCS_PRIO for those cells that meet the criterion H> = 0.

- all measured cells, excluding HCS priority levels, if no cell meets the criterion H> = 0.

According to the above, if the UE is in low mobility mode and there is a cell with H> = 0, the UE performs the following steps:

Step 1. Perform the necessary measurements.

Stage 2. Checking whether or not there are cells that meet the criterion H> = 0.

Step 3. Identification of the highest HCS_PRIO of the cells verified in step 2.

Step 4. Cell identification with HCS_PRIO identified in step 3.

Step 5. Verification of cells that meet criterion S from the cells identified in step 4.

Step 6. Perform the ranking for the cells identified in step 5.

The procedure generally works in a scenario in which a cell with the highest HCS_PRIO and H> = 0 satisfies criterion S. But if the cell with the highest HCS_PRIO and H> = 0 does not satisfy criterion S, the UE cannot select a cell. An example of a cell (A, B, C) and their characteristics may be as follows:

Honeycomb Criterion H Criterion S HCS_PRIO A Satisfied Not satisfied four B Not satisfied Satisfied four C Satisfied Satisfied 3

The following may result from applying the above steps:

Step 1. Perform the necessary measurement.

Cells A, B and C are measured.

Stage 2. Checking whether or not there are cells that meet the criterion H> = 0.

Cells A and C satisfy criterion H.

Step 3. Identification of the highest HCS_PRIO of the cells verified in step 2.

Between A and C, A has the highest HCS_PRIO, which is 4.

Step 4. Cell identification with HCS_PRIO identified in step 3.

Cell A is the only cell with the highest HCS_PRIO.

Step 5. Verification of cells that meet criterion S from the cells identified in step 4.

Cell A does not satisfy criterion S.

Step 6. Perform the ranking for the cells identified in step 5.

There is no candidate cell for ranking.

Thus, in the above scenario, although there are cells that satisfy criterion S, there are no cells in the ranking list. This leads to a problem since the UE cannot reselect the cell with the best quality.

The prior art is usually described under the assumption that there are always cells for ranking, and does not indicate anything for the case where there are no cells for ranking. Thus, the operation mode of the UE after step 6 in the above scenario is not clear. Accordingly, this may lead to an ununified mode of operation of the UE. The following interpretations may be considered.

Option 1: After notifying that there is no cell to be ranked as the result of step 6, the UE declares “no network”. As a result, the UE searches for the initial cell, which leads to a long interrupt time.

Option 2: The UE does nothing. Thus, since there are no cells to be ranked, the UE remains anchored in the current serving cell. But this raises questions, since the serving cell is usually considered in candidate cells for the ranking process. And until the criterion S is satisfied for the service, the UE remains anchored in a non-best cell.

One way to correct such a problem is for the UE to consider both criterion H and criterion S when selecting candidate cells for ranking. Due to this, cases where there are no candidate candidate cells for ranking, even when there are cells that satisfies the S criterion, can be avoided with benefit.

Details # 2

Agreement A

According to the above description, the first possible implementation is that the UE first checks the criterion H, and then checks the criterion S.

In this implementation, if the UE is in low mobility mode and there is a cell with H> = 0, the UE performs the following steps:

Step 1. Perform the necessary measurement.

Stage 2. Checking whether or not there are cells that meet the criterion H> = 0.

Step 3. Identification of the highest HCS_PRIO of the cells verified in step 2.

Step 4. Cell identification with HCS_PRIO identified in step 3.

Step 5. Verification of cells that meet criterion S from the cells identified in step 4.

Step 6. Perform the ranking for the cells identified in step 5.

Agreement B

Another possible implementation is that the UE first checks the criterion S, and then checks the criterion H.

In this implementation, if the UE is in low mobility mode and there is a cell with H> = 0, the UE performs the following steps:

Step 1. Perform the necessary measurement.

Step 2. Check whether or not there are cells that meet the criteria S.

Stage 3. Checking whether or not there are cells that meet the criterion H> = 0 of the cells checked in stage 2.

Step 4. Identification of the highest HCS_PRIO of the cells verified in step 3.

Step 5. Cell identification with HCS_PRIO identified in step 4.

Step 6. Perform the ranking for the cells identified in step 5.

Next, the operation mode of the UE is analyzed according to the above conventions A and B. The following exemplary scenario may be considered:

Honeycomb Criterion H Criterion S HCS_PRIO A Satisfied Not satisfied four B Not satisfied Satisfied four C Satisfied Satisfied 3

Cell reselection as per agreement A

According to the procedure described above, the following steps can be carried out:

Step 1. Perform the necessary measurement.

Cells A, B and C are measured.

Stage 2. Checking whether or not there are cells that meet the criterion H> = 0.

Cells A and C satisfy criterion H.

Step 3. Identification of the highest HCS_PRIO of the cells verified in step 2.

Between A and C, A has the highest HCS_PRIO, which is 4.

Step 4. Cell identification with HCS_PRIO identified in step 3.

Cell A is the only cell with the highest HCS_PRIO.

Step 5. Verification of cells that meet criterion S from the cells identified in step 4.

Cell A does not satisfy criterion S.

Step 6. Perform the ranking for the cells identified in step 5.

There are no hundreds of candidate candidates for ranking.

Cell reselection as per agreement B

According to the procedure described above, the following steps can be carried out:

Step 1. Perform the necessary measurement.

Cells A, B and C are measured.

Step 2. Check whether or not there are cells that meet the criteria S.

Cells B and C satisfy criterion S.

Stage 3. Checking whether or not there are cells that meet the criterion H> = 0 of the cells checked in stage 2.

Between B and C, C satisfies criterion H.

Step 4. Identification of the highest HCS_PRIO of the cells verified in step 3.

C has the highest HCS_PRIO, which is 3.

Step 5. Cell identification with HCS_PRIO identified in step 4.

Cell C is the only cell with the highest HCS_PRIO.

Step 6. Perform the ranking for the cells identified in step 5.

Cell C is a ranking candidate cell.

Correction of various operating modes

When considering the above scenarios, it is obvious that there is a cell candidate for the UE to consolidate. Cell C satisfies both criterion H and criterion S. However, there is a cell to rank in agreement B, but there are no cells for ranking in agreement A. The operation mode of agreement A leads to a problem because the UE cannot reselect not a single relevant honeycomb. The UE may declare “network absent” and begin a full search, resulting in a long interrupt time.

The main problem with implementing A is that criterion S is not properly considered when choosing the highest HCS_PRIO value (i.e., a cell that does not meet criterion S but satisfies criterion H affects the decision making process for the highest HCS_PRIO). Thus, the procedures of the prior art should be adjusted so that criterion S is also considered in the steps associated with criterion H.

Proposition 1: A cell satisfying criterion S is considered in the process associated with criterion H.

The foregoing is generally described under the assumption that there are always several hundred to rank. However, the prior art does not indicate anything for the case where there are no cells for ranking. Thus, the operation mode of the UE when there are no cells for ranking is not clear. Accordingly, this may lead to an ununified mode of operation of the UE.

Proposal 2: It is proposed to discuss whether or not there is a need to indicate any features for the case where there are no cells for ranking.

The easiest way to correct this problem is that the UE considers both criterion H and criterion S when selecting candidate cells for ranking. Due to this, the case can be prevented when there are no candidate candidate cells for ranking, even when there are cells that satisfy the S criterion.

Cell reselection evaluation process

Cell reselection criteria

The following cell reselection criteria are used for intra-frequency cells, inter-frequency cells, and cells between RAT technologies:

The criterion H of the threshold level of quality level for hierarchical cellular structures is used to determine whether or not prioritized ranking should be applied according to the hierarchical rules of cell reselection, and is defined by the following:

If the system information (SI) indicates that HCS is not used, the criterion H of the quality level threshold value is not applied. The cell ranking criterion R is set:

where: the reported Q _{offmbms value} applies only to cells (serving or neighboring cells) belonging to MBMS PL, and where:

TEMP_OFFSETn applies the offset to the H and R criteria for PENALTY_TIMEn after the Tn timer is started for this neighboring cell.

TEMP_OFFSETn and PENALTY_TIMEn are only applicable if HCS usage is indicated in the system information.

A timer Tn is implemented for each neighboring cell. Tn must be started from scratch when one of the following conditions becomes true:

- if HCS_PRIOn <> HCS_PRIOs and Q _{meas, n} > = Q _hcsn

Or:

- if HCS_PRIOn = HCS_PRIOs, and

- for serving FDD and neighboring FDD cells, if the quality score for cell selection and reselection is set to CPICH RSCP in the serving cell, and:

Q _{meas, n} > Q _{meas, s} + Q _{offset1s, n}

- for serving FDD and neighboring FDD cells, if the quality score for cell selection and reselection is set to CPICH Ec / No in the serving cell and:

Q _{meas, n} > Q _{meas, s} + Q _{offset2s, n}

- for all other serving and neighboring cells: Q _{meas, n} > Q _{meas, s} + Q _{offset1s, n}

Tn for the associated neighboring cell should be stopped when any of the above conditions are no longer fulfilled. Any value computed for TOn is valid only if the associated timer Tn is still running; otherwise, TOn must be set to zero.

When a cell is re-selected, the timer Tn is stopped only if the corresponding cell is not a neighboring cell for the new serving cell or if the criteria provided above to start the Tn timer for the corresponding cell no longer matches the parameters of the new serving cell. When reselecting a cell, the timer Tn should continue to operate for the respective cells, but the criteria above should be evaluated using the parameters transmitted in the broadcast mode in the new serving cell, if the corresponding cells are neighbors of the new serving cell.

Sn The cell selection value of the neighboring cell, (dB) Qmeas The value of quality. The received signal quality value extracted from the averaged CPICH Ec / No or CPICH RSCP for FDD cells, from the averaged P-CCPCH RSCP for TDD cells, and from the averaged received signal level for GSM cells. Averaging of these values for measurement is performed as indicated in [10] and [11]. For FDD cells, the measurement that is used to retrieve the quality value is specified by the information element of the cell quality selection and reselection metric.

Broadcasting cell reselection parameters in system information may be provided. The cell selection criterion S used for cell reselection is satisfied when:

for FDD cells: Srxlev> 0 and Squal> 0 for TDD cells: Srxlev> 0 for GSM cells: Srxlev> 0

Where:

Squal Cell selection quality value (dB), applicable only to FDD cells Srxlev Cell Select RX Level (dB) Qqualmeas Measured cell quality value. Received signal quality is expressed in CPICH Ec / No (dB) for FDD cells. CPICH Ec / N0 should be averaged, as indicated in [10]. Applicable only to FDD cells Qrxlevmeas The measured value of the RX level of the cell. These are the received signal, CPICH RSCP for FDD cells (dBm), P-CCPCH RSCP for TDD cells (dBm), and the average received signal level, as indicated in [10], for GSM cells (dBm). CPICH RSCP, P-CCPCH RSCP and received signal strength for GSM cells should be averaged as indicated in [10] and [11] Qqualmin Minimum required cell quality level (dB). Applicable only to FDD cells. Qrxlevmin Minimum RX cell level required (dBm) Pcompensation max (UE_TXPWR_MAX_RACH-P_MAX, 0) (dB) UE_TXPWR_MAX_RACH The maximum level of TX power that the UE can use when accessing a cell via RACH (read in system information) (dBm) P_MAX UE Maximum Output RF Power (dBm)

If HCS is not used in the serving cell, then the UE shall perform a ranking of all cells that meet the criterion S from:

- all measured cells.

If HCS is to be used in a serving cell, then the UE must perform a ranking of all cells from:

1. low mobility

- all measured cells that have the highest HCS_PRIO for those cells that meet the criterion H> = 0 and meet the criterion S.

- all the measured cells that meet the criterion S, without taking into account the levels of HCS priority, if no cell meets both the criterion H> = 0 and the criterion S.

2. in high mobility mode

- all measured cells and their cells:

- if there are cells with a lower HCS priority than the serving cell, which meet both the criterion H> = 0 and the criterion S:

- from cells that have a lower HCS priority than the serving cell, of all cells that have the highest HCS_PRIO for those cells that meet both the criterion H> = 0 and the criterion S;

- otherwise:

- if there are cells that meet both the criterion H> = 0 and the criterion S with HCS priority greater than or equal to the HCS priority of the serving cell:

- from cells that have an HCS priority higher than or equal to the HCS priority of a serving cell, all cells that have the lowest HCS_PRIO for those cells that meet the criterion H> = 0 and meet the criterion S;

- otherwise:

- all cells that meet the criterion S without taking into account the levels of HCS priority.

Cells must be ranked according to the R criteria specified above, extracting Q _{meas, n} and Q _{meas, s} and calculating R values using CPICH RSCP, P-CCPCH RSCP and average received signal strength for FDD, TDD and GSM cells, respectively .

The offset Q _{offset1s, n is} used for Q _{offsets, n} to calculate Rn, the hysteresis Q _{hyst1s is} used for Q _hysts to calculate Rs. For UEs in CELL_PCH or URA_PCH RRC connection states, the hysteresis Q _hysts takes the value Q _{hyst1s, PCH} to calculate Rs if provided in SIB4. For a UE in the RRC connection state CELL_FACH, the hysteresis Q _hysts takes the value Q _{hyst1s, FACH} , to calculate Rs if provided in SIB4.

If HCS usage is indicated in the system information, TEMP_OFFSET1n is used for TEMP_OFFSETn to calculate TOn. If the system information indicates that HCS is not used, TEMP_OFFSETn is not used in calculating Rn. The best ranked cell is the one with the highest R.

If the TDD or GSM cell is ranked as the best cell, then the UE must perform cell reselection in that TDD or GSM cell.

If the FDD cell is ranked as the best cell, and the quality score for cell selection and reselection is set to CPICH RSCP, then the UE must perform cell reselection in this FDD cell. If it is found that this cell is not suitable, then the UE should operate in an appropriate mode.

If the FDD cell is ranked as the best cell, and the quality score for cell selection and reselection is set to CPICH Ec / No, then the UE must perform a second ranking of the FDD cells according to the R criteria specified above, but by measuring the CPICH Ec / No to extract Q _{meas, n} and Q _{meas, s} and calculate the values of R FDD cells. Offset Q _{offset2s, n is} used for Q _{offsets, n} to calculate Rn, hysteresis Q _{hyst2s is} used for Q _hysts to calculate Rs. For UEs in CELL_PCH or URA_PCH RRC connection states, the hysteresis Q _hysts takes the value Q _{hyst2s, PCH} to calculate Rs if provided in SIB4. For a UE in _RLL connection state CELL_FACH, the hysteresis Q _hysts takes the value Q _{hyst2s, FACH} , to calculate Rs if provided in SIB4. If HCS usage is indicated in the system information, TEMP_OFFSET2n is used to calculate TOn. If the system information indicates that HCS is not used, TEMP_OFFSETn is not used in calculating Rn. After this second ranking, the UE must reselect the best ranked FDD cell. If it is found that this cell is not suitable, then the UE should operate in an appropriate mode.

In all cases, the UE should re-select a new cell only if the following conditions are satisfied:

- the new cell has a better rank than the serving cell during the Treselection time interval. For UEs in CELL_PCH or URA_PCH RRC connection states, the Treselection _{s, PCH} interval is applied if provided in SIB4, while for UEs in CELL_FACH RRC connection state, the Treselection _{s, FACH} interval is applied if provided in SIB4. For hierarchical cellular structures, when a state with high mobility is not detected, if, according to the HCS rules, the serving cell is not ranked, then all the ranked cells are considered to have a better rank than the serving cell.

Additionally, the UE must apply the following scaling rules to Treselections or Treselection _{s, PCH} or Treselection _{s, FACH} :

- For intra-frequency cells and with an undetected state with high mobility:

- scaling is not applied.

- For intra-frequency cells and with a detected state with high mobility:

- Multiplication of Treselections or Treselection _{s, PCH} or Treselection _{s, FACH} by IE "Speed dependent ScalingFactor for_Treselection", if sent in the system information.

- For inter-frequency cells and with an undetected state with high mobility:

- Multiplication of Treselections or Treselection _{s, PCH} or Treselection _{s, FACH} by IE "Inter-Frequency ScalingFactor for Treselection", if sent in the system information.

- For inter-frequency cells and with a detected state with high mobility:

- Multiplication of Treselections or Treselection _{s, PCH} or Treselection _{s, FACH} by IE "Speed dependent ScalingFactor for_Treselection", if sent in system information, and by "Inter-Frequency ScalingFactor for Treselection", if sent in system information.

- For cells between RAT technologies and with undetected state with high mobility:

- Multiplication of Treselections or Treselection _{s, PCH} or Treselection _{s, FACH} by IE "Inter-RAT ScalingFactor for Treselection", if sent in the system information.

- For cells between RAT technologies and with a detected state with high mobility:

- Multiplication of Treselections or Treselection _{s, PCH} or Treselection _{s, FACH} by IE "Speed dependent ScalingFactor for_Treselection" if sent in system information, and "Inter-RAT ScalingFactor for Treselection" if sent in system information.

If scaling is applied to Treselections or Treselection _{s, PCH} , UE should round up the result after all scaling to the nearest second. If scaling is applied to Treselection _{s, FACH} , the UE should round up the result after all scaling to the nearest 0.2 seconds.

- More than 1 second has elapsed since the UE is anchored in the current serving cell. As described above, various exemplary embodiments of the present invention relate to a method for selecting a cell in a hierarchical cellular structure based on cell quality, which leads to more efficient use of radio resources.

The present invention provides a cell selection method for a subscriber unit (UE), which comprises the steps of verifying whether or not a hierarchical cellular structure (HCS) is being used; reading a parameter associated with the H criteria from the system information; performing cell measurement; identification of cells that meet the criteria S of the measured cells; checking criteria H for a cell that satisfies criteria S; and selecting a cell having the highest criteria R from cells that satisfy both criteria S and criteria H.

HCS defines a certain number of overlapping cells of various sizes that form several cell levels, and is used if the serving cell of the UE belongs to the HCS. S criteria are selection or eligibility criteria used to check whether the reception quality of a candidate cell is sufficient or not, criteria H are HCS criteria used when HCS is used, which are a positive or negative value calculated based on information sent to the system information, and the R criteria is the ranking criterion used by the mobile terminal to rank the list of cells satisfying the S criterion. The measured cells are determined by performing the procedure ur signal measurement using the base station in all searchable frequency bands, and then the cell having the strongest signal characteristics value is selected from cells that satisfy certain cell selection conditions, and the selected cell is accessed.

In addition, the present invention provides a method for selecting a cell for a subscriber unit (UE), the method comprising the steps of: if a hierarchical cell structure (HCS) is used in a serving cell of the UE when the UE has low mobility, a ranking procedure is performed for all measured cells that have the highest HCS priority of those cells that meet criterion S and criterion H≥0, or the ranking procedure is performed for all measured cells regardless of HCS priorities, if no cell matches eriyu S and the criterion H≥0; and when the UE has high mobility, a ranking procedure is performed for all measured cells, and from these measured cells, if there are cells with a lower HCS priority than the serving cell that meets the criterion S and the criterion H≥0, then from the cells that have a lower HCS priority than the serving cell, the ranking procedure is performed for all cells that have the highest HCS priority of those cells that meet criterion S and criterion H≥0, otherwise, if there are cells that match criterion S and criterion H≥0 with HCS Priori for a cell that is greater than or equal to the HCS priority of the serving cell, then of the cells that have HCS priority that is greater than or equal to the HCS priority of the serving cell, a ranking procedure is performed for all cells that have the lowest HCS priority of those cells that correspond to the criterion S and the criterion H≥0, otherwise, the ranking procedure is performed for all cells, regardless of HCS priorities.

A hierarchical honeycomb structure (HCS) defines a certain number of overlapping cells of various sizes that form several levels of cells. A UE is deemed to have low mobility or high mobility based on the number of cell re-selections for a specific period of time or based on RRC signaling from the network. The measured cells are determined by performing signal measurement procedures using the base station in all searchable frequency bands, and then the cell having the strongest signal characteristics value is selected from the cells that satisfy certain cell selection conditions, and the selected cell is accessed. At least one of CPICH RSCP, CPHIC Ec / N0, and Carrier RSSI is used in signal measurement procedures.

The ranking procedure leads to a ranking that demonstrates the relative signal intensities of the measured cells or the degree of overlap between the cells, after considering both criterion H and criterion S when selecting candidate candidates for ranking. The ranking procedure is performed based on the R criterion, and cell selection or reselection is performed for one or more cells ranked so as to have the best quality. HCS priority means specifying at what level of HCS cells the UE should be. The HCS priority is transmitted as part of the broadcast information in the cell in the form of system information blocks, and alternatively, for neighboring cells, the HCS priority is transmitted as part of the RRC measurement control message. Criterion S is a selection or eligibility criterion used to check whether the reception quality of a candidate cell is sufficient or not, and criterion H is an HCS criterion used when HCS is used, which is a positive or negative value calculated on based on the information sent in the system information and the measurements from the CPICH / P-CPCCH of the candidate cell.

Various features and principles described herein may be implemented in software, hardware, or a combination of the above. For example, a computer program (which runs in a computer, terminal, or network device) for a method and system for processing a cell selection method in a hierarchical cellular structure based on cell quality may comprise one or more segments of program code for performing various tasks. Similarly, a software tool (which runs on a computer, terminal, or network device) for a method and system for processing a cell selection method in a hierarchical cell structure based on cell quality may contain pieces of program code for performing various tasks.

The method and system for processing a cell selection method in a hierarchical cell structure based on cell quality according to the present invention is compatible with various types of technologies and standards. Certain principles described herein are associated with various types of standards such as GSM, 3GPP, LTE, IEEE, 4G, and the like. However, it can be understood that the above exemplary standards do not intend to be limited, since other related standards and technologies should also be applicable to the various features and principles described herein.

Industrial applicability

The features and principles in this document are applicable and can be implemented in various types of user devices (for example, mobile terminals, portable phones, wireless devices, etc.) and / or network objects that can be configured to support the method cell selection in a hierarchical cell structure based on cell quality.

Since the various principles and features described herein can be implemented in several forms without departing from their characteristics, it should also be understood that the above described embodiments are not limited to any details of the above description, unless otherwise indicated, but should instead be considered in a broad sense within the scope specified in the attached claims. Therefore, all changes and modifications that are within the scope of this scope or its equivalents, thereby have the intention to be covered by the attached claims.

Claims (14)

1. A method for selecting a cell for a subscriber unit (UE), the method comprising the steps of:
- check whether or not a hierarchical cellular structure (HCS) is used;
- read the parameter associated with the criteria N from the system information;
- perform cell measurement;
- identify cells that meet the criteria S of the measured cells;
- check the criteria H for a cell that meets the criteria S; and
- choose a cell having the highest criteria R from cells that satisfy both criteria S and criteria N. 2. The method according to claim 1, in which the HCS defines a certain number of overlapping cells of various sizes that form several levels of cells, and is used if the serving cell of the UE belongs to the HCS. 3. The method according to claim 1, in which the criteria S are the selection or eligibility criteria used to check whether the reception quality of the candidate cell is sufficient or not, criteria H are HCS criteria used when HCS is used, which are a positive or negative value calculated based on the information sent in the system information, and the R criteria is a ranking criterion used by the UE to rank a list of cells that satisfy the S criterion. 4. The method according to claim 1, in which the measured cells are determined by performing signal measurement procedures using the base station in all searchable frequency bands, and then the cell having the strongest signal characteristics value is selected from cells that satisfy certain selection conditions cell, and access to the selected cell. 5. A method for selecting a cell for a subscriber unit (UE), the method comprising the steps of:
- if a hierarchical cellular structure (HCS) is used in a serving cell of the UE when the UE has low mobility,
- the ranking procedure is performed for all measured cells that have the highest HCS priority of those cells that meet the criterion S and the criterion Н≥0, or the ranking procedure is performed for all measured cells regardless of HCS priorities, if no cell meets the criterion S and criterion H≥0; and
- when the UE has high mobility,
- a ranking procedure is performed for all measured cells, and of these measured cells,
- if there are cells with a lower HCS priority than the serving cell that meets the S criterion and the criterion H≥0, then of the cells that have a lower HCS priority than the serving cell, the ranking procedure is performed for all cells that have the highest HCS priority of those cells that meet the criterion S and the criterion H≥0, otherwise,
- if there are cells that meet criterion S and criterion H≥0 with HCS priority that is greater than or equal to the HCS priority of the serving cell, then out of cells that have HCS priority that is greater than or equal to the HCS priority of the serving cell, the procedure the ranking is performed for all cells that have the lowest HCS priority of those cells that meet the criterion S and the criterion H≥0, otherwise, the ranking procedure is performed for all cells regardless of HCS priorities. 6. The method according to claim 5, in which the hierarchical cell structure (HCS) defines a certain number of overlapping cells of various sizes, which form several levels of cells. 7. The method according to claim 5, in which the UE is considered to have low mobility or high mobility based on the number of cell reselections over a specific period of time or based on RRC signaling from the network. 8. The method according to claim 5, in which the measured cells are determined by performing signal measurement procedures using the base station in all searchable frequency bands, and then the cell having the strongest signal characteristics value is selected from cells that satisfy certain selection conditions cell, and access to the selected cell. 9. The method of claim 8, wherein at least one of CPICH RSCP, EC / NO CPHIC, and Carrier RSSI is used in signal measurement procedures. 10. The method according to claim 5, in which the ranking procedure leads to a ranking that demonstrates the relative signal intensities of the measured cells or the degree of overlap between the cells, after considering both criterion H and criterion S when selecting candidate candidates for ranking. 11. The method of claim 10, wherein the ranking procedure is performed based on criterion R, and cell selection or reselection is performed for one or more cells ranked so as to have the best quality. 12. The method according to claim 5, in which the HCS priority means setting at what level the HCS cells should be a UE. 13. The method of claim 12, wherein the HCS priority is transmitted as part of the broadcast information in the cell in the form of system information blocks, and alternatively, for neighboring cells, the HCS priority is transmitted as part of the RRC measurement control message. 14. The method according to claim 5, in which the criterion S is a selection or eligibility criterion used to check whether the reception quality of the candidate cell is sufficient or not, and criterion H is the HCS criterion used when HCS is used and which is a positive or negative value calculated based on information sent in the system information and measurements from the CPICH / P-CPCCH of the candidate cell.

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