HK1168231A - Method and apparatus of resolving pci confusion for providing inbound mobility to closed subscriber group - Google Patents

Description

Method and apparatus for resolving PCI confusion for providing inbound mobility to closed subscriber groups

Cross Reference to Related Applications

This application claims the benefit of the following applications: united states provisional application No. 61/169,190 filed on 14.4.2009; united states provisional application No. 61/185,793 filed on 10.6.2009; united states provisional application No. 61/218,820 filed on 19.6.2009; united states provisional application No. 61/220,226 filed on 25.6.2009; and U.S. provisional application No. 61/255,251 filed on 27/10/2009. All of these applications are incorporated herein by reference in their entirety.

Technical Field

The present invention relates to wireless communications.

Background

Basic support for operation in using a Home Node B (HNB) or a home evolved node b (henb) (hereinafter collectively referred to as HNB) has been introduced in release 8 of the third generation partnership project (3GPP) specifications for Wideband Code Division Multiple Access (WCDMA), Long Term Evolution (LTE) and other cellular standards. HNBs are similar to Wireless Local Area Network (WLAN) Access Points (APs) and are designed in a manner to provide cellular service access to users over a very small service area (e.g., home or small office). This is useful for areas where cellular networks have not been deployed, or where there is conventional Radio Access Technology (RAT) coverage, and where cellular coverage is weak or non-existent for radio related reasons (e.g., metro or shopping malls). A user (e.g., an individual or an organization) may use the HNB over an area where the service is needed.

The HNB may be configured as a closed (closed) subscriber group (CSG) cell or a hybrid cell. The CSG cell is accessible only to the CSG members. The hybrid cell is accessible to any wireless transmit/receive unit (WTRU) but may provide better or privileged service or quality of service (QoS) to CSG members.

Fig. 1 shows an example of a conventional HeNB configuration in a wireless communication system 100. The wireless communication system 100 includes an LTE macro cell 105, a 3GPP system cell 110, an upper network node (e.g., gateway) 115, and/or a Mobility Management Entity (MME)/serving General Packet Radio Service (GPRS) support node (SGSN) 120. The upper network node 115 is responsible for coordinating the operation of several henbs 125A, 125B and 125C. Alternatively, the MME/SGSN 120 may be responsible for coordinating the operation of the henbs 125A, 125B, and 125C. MME is the LTE equivalent of 3G/2G SGSN. The relationship between the LTE macrocell 105 and the 3GPP system 110 (e.g., WCDMA/global system for mobile communications (GSM)) is the coverage area where there may be overlap of the two technologies. The overlap in coverage is similar to simultaneous coverage of GSM and WCDMA technologies. The upper network node 115 may be a gateway function connected with the MME/SGSN 120. As a gateway, the role of the higher network node 115 may be to act as a single macro cell towards the MME/SGSN 120 while supporting several small home cells.

Figure 2 shows an LTE wireless communication system 200 that includes a WTRU 205, a serving CSG cell 210, and a neighboring CSG cell 215. To complete an inbound (inbound) handover for a CSG cell in the LTE wireless communication system 200, the WTRU 205 needs to measure and report the CSG cell to the network. However, CSG cells are prone to physical layer cell identity (PCI) confusion, which occurs when two different CSG cells in the vicinity of the Radio Network Controller (RNC) or eNB to which the WTRU is initially connected use the same PCI. PCI confusion may also occur if a WTRU has to handover into a CSG cell (e.g., a hybrid cell) of which the WTRU is not a member. A solution that has been proposed for WTRUs is to report the CSG Cell Global Identity (CGI) to the network. Alternatively, another proposed solution for the network is for the network to resolve PCI confusion itself (i.e., map PCI to CGI) and then request the WTRU to report CGI when a handover occurs, if needed. It would be desirable to have a reliable method and apparatus for resolving PCI confusion.

Disclosure of Invention

A method and apparatus for providing inbound mobility to CSG and hybrid cells is described. The WTRU reads the CGIs of the neighboring cells and reports it to the network of the CSG cell. The network then maps the PCI of the CSG cell onto the CGI and requests the WTRU to read the CGI at handover, if needed.

Drawings

The invention will be understood in more detail from the following description, given by way of example and understood in conjunction with the accompanying drawings, in which:

fig. 1 shows an example of a conventional HeNB configuration in a wireless communication system;

figure 2 shows an LTE wireless communication system according to one embodiment;

fig. 3 illustrates an LTE wireless communication system/access network;

fig. 4 illustrates an example of the LTE wireless communication system shown in fig. 3;

figure 5 illustrates a WTRU-based method of measuring and reporting SI to a network in a neighboring CSG cell;

fig. 6 is a block diagram illustrating a WTRU-based procedure for reading neighboring cell SI for CGI;

FIG. 7 illustrates a flow diagram of a method of determining validity for a PCI to CGI mapping in accordance with one embodiment;

FIG. 8 shows a block diagram of a method for determining the validity of a PCI-to-CGI mapping, in accordance with another embodiment;

fig. 9 shows a procedure for reporting CGI to a source cell;

fig. 10 shows a process for requesting an interval from a source cell;

figure 11 shows a process for a WTRU reading the SI of a neighboring CSG cell and allocating reception resources in the WTRU; and

figure 12 shows an example of a block diagram of a WTRU receiving a cell broadcast and reading neighboring CSG cells.

Detailed Description

The term "wireless transmit/receive unit (WTRU)" as referred to below includes, but is not limited to, a User Equipment (UE), a mobile station, a fixed or mobile subscriber unit, a pager, a cellular telephone, a Personal Digital Assistant (PDA), a computer, or any other type of user equipment capable of operating in a wireless environment.

The term "evolved node-b (enb)" referred to below includes, but is not limited to, a base station, a site controller, an Access Point (AP), or any other type of interfacing device capable of operating in a wireless environment.

In the following embodiments, the term "measurement report" may be used to refer to a Radio Resource Control (RRC) message. Furthermore, the term "CSG identity" or "hybrid or CSG cell identity" may refer to a CGI (CSG identifier), or more generally, any measurement taken to facilitate the network in identifying the CSG or hybrid cell of a cell, such as timing differences between a serving cell and the CSG or hybrid cell.

Fig. 3 illustrates a Long Term Evolution (LTE) wireless communication system/access network 300 that includes an evolved universal terrestrial radio access network (E-UTRAN) 305. The E-UTRAN 305 includes several evolved node Bs (eNBs) 320 and a home evolved node B (HeNB) 360. The WTRU310 communicates with the eNB 320 and the h (e) NB 360. enbs 320 are connected to each other using an X2 interface. Each eNB 320 is connected with a Mobility Management Entity (MME)/serving gateway (S-GW)330 through an S1 interface. The HeNB360 is also connected to a HeNB gateway (HeNB GW)370 through an S1 interface. The HeNB360 and the HeNBGW 370 are connected to the MME/S-GW330 through an S1 interface. The HeNB GW 370 appears to the MME/S-GW330 as eNB 320. The HeNB GW 370 appears to the HeNB360 as MME/S-GW 330.

Although a single WTRU310, three enbs 320 and three henbs 360 are shown in fig. 3, it should be apparent that any combination of wireless and wired devices may be included in the wireless communication system/access network 300.

Figure 4 shows one example of an LTE wireless communication system 400 that includes a WTRU310, an eNB 320, and an MME/S-GW 330. As shown in fig. 4, the WTRU310, eNB 320, and MME/S-GW330 are configured to perform a method for resolving PCI confusion for inbound mobility for CSG cells and hybrid cells.

In addition to components found in a typical WTRU, the WTRU310 includes a processor 416 with an optional linked memory 422, at least one transceiver 414, an optional battery 420, and an antenna 418. The processor 416 is configured to perform a method of resolving PCI confusion for inbound mobility for CSG cells and hybrid cells. The transceiver 414 is in communication with the processor 416 and the antenna 418 to facilitate the transmission and reception of wireless communications. If a battery 420 is used in the WTRU310, the battery 420 powers the transceiver 414 and the processor 416.

In addition to components found in a typical eNB, eNB 320 includes a processor 417 with an optional linked memory 415, a transceiver 419, and an antenna 421. The processor 417 is configured to perform a method for resolving PCI confusion for inbound mobility for CSG cells and hybrid cells.

The transceiver 419 is in communication with the processor 417 and the antenna 421 to facilitate the transmission and reception of wireless communications. The eNB 320 is connected to an MME/S-GW330, which MME/S-GW330 includes a processor 433 with an optional linked memory 434. The MME/S-GW330, eNB 320 and WTRU310 communicate with the HeNB 360.

The HeNB may include a processor for processing data and commands, a transmitter for transmitting information, a receiver for receiving data, and an antenna coupled to the transmitter and receiver for transmitting and receiving status over a wireless interface.

It should be understood that the concepts described herein are also applicable to other wireless technologies, such as Universal Mobile Telecommunications System (UMTS). In the case of UMTS, an equivalent term for PCI may be Primary Scrambling Code (PSC).

Two approaches are proposed. The WTRU310 is configured to read CGIs of neighboring cells and report them to the network. And, the network is configured to map the PCI of the CSG cell to the CGI. For example, the network may signal different predefined thresholds for the serving cell and the neighboring cells. The WTRU310 may report the serving cell to the network when the serving cell is above an upper threshold or below a lower threshold. The WTRU310 may use a similar reporting method for neighboring cells. Based on the signal strength or signal quality of the serving cell or CSG neighbor cell, the network may decide whether to request the WTRU310 to read neighbor cell System Information (SI) for CGI or to resolve PCI confusion itself. The network may also use existing thresholds for event reporting instead of determining new thresholds.

If the signal strength or signal quality of the serving cell is above a threshold, the network requests the WTRU310 to report the CGI of the CSG neighbor cell, regardless of the signal strength or quality of the neighbor cell. Depending on the signal strength or quality of the CSG neighbor cell, the network may determine whether a smaller gap duration (gap) is sufficient for the WTRU310 to read the SI of the neighbor cell(s), or whether a larger DRX cycle period is required. If the CSG neighbor cell is strong, the WTRU310 is able to read the neighbor cell SI and thus requires a smaller gap duration. Alternatively, the WTRU310 may automatically determine the required interval duration based on the channel reception quality of the neighboring cells and send the required interval duration to the network.

Alternatively, if the signal strength or signal quality of the serving cell is below a threshold, the network resolves the PCI confusion itself. Based on the signal strength or quality strength in the neighbor cells, the network may or may not request the WTRU310 to read the SI of the CSG neighbor cell at handover to determine whether the CSG neighbor cell is on the white list of the WTRU 310. If the neighbor cell signal strength or quality is not strong enough, the network may not request the WTRU310 to read the SI of the neighbor cell at the time of handover. If the neighbor cell signal strength is strong, the network may request the WTRU310 to read the SI of the neighbor cell at the time of handover, since the WTRU310 can read the SI at the very first time. The WTRU310 may also use a signal strength or signal quality threshold of the CSG neighbor cell. The WTRU310 knows whether it should attempt to read the SI of the CSG cell at handover based on the signal strength or quality of the cell at handover or a certain period of time before handover. The signal strength or signal quality threshold may be predefined or signaled by the network in advance.

Figure 5 illustrates a WTRU-based method 500 for measuring SI of neighboring CSG cells and reporting the SI to a network. The WTRU310 is configured to receive a high threshold and a low threshold for a current serving cell and at least one neighboring CSG cell (501). The WTRU310 is configured to monitor the signal strength of the current serving cell (503) and configured to compare the measured signal strength to a low threshold of the serving cell. If the measured signal strength is below the serving cell's low threshold (505), the WTRU310 starts reading the SI from the neighboring CSG cell (507). The WTRU310 sends a measurement report including the SI of the neighboring CSG cell (509). The measurement report may include the signal strength or signal quality of the cell identified by its PCI. The measurement report may also include information, including but not limited to CGI, contained in the SI of the neighboring CSG cell.

Fig. 6 is a block diagram illustrating a WTRU-based process 600 for reading neighboring cell SI, denoted CGI. The WTRU310 determines if it has sufficient idle time from Discontinuous Reception (DRX) (605) and when the WTRU310 determines that the CSG neighbor cell is above the threshold (610), it reads the CSG neighbor cell SI (620). The threshold (above which CSG neighbor cells need to be) may be signaled by the network on the SI or in a dedicated RRC message, or may be automatically determined by the WTRU. Also, there may be a minimum period of the DRX cycle for the WTRU310 to read the neighboring cell SI. The minimum length may be signaled by the network in the SI or in a dedicated RRC message. The signal strength threshold and the minimum period of the DRX cycle may be received by dedicated or broadcast RRC signaling.

In addition, there is a threshold that allows the WTRU310 to implicitly extend the DRX duration and thus the timing for performing measurements on CSG neighbor cells.

If the WTRU310 is able to read the CGIs of the CSG neighboring cells (620), the WTRU310 may be configured to send a measurement report to the network indicating that it has resolved the PCI confusion (630). The measurement report may include the PCIs of the CSG neighbor cell, an Information Element (IE) indicating that PCI confusion is resolved, and optionally, the neighbor cell CGIs. Thus, there may be two measurement reports for a particular neighbor cell, whereby a first measurement report is sent when the CSG neighbor cell signal strength reaches or crosses a certain threshold, and a second measurement report is sent when the WTRU310 reads the CSG neighbor cell SI. Alternatively, the WTRU310 may combine the two measurement reports into one measurement report by attempting to read the neighboring cell SI while a timing-triggered (TTT) timer is running. When a measurement report is triggered by an event, the measurement report is only sent when the sending condition has been true for the TTT. The neighbor cell CGI SI may also be piggybacked as part of an existing RRC message.

If the WTRU310 has no idle time from DRX available to read CSG neighbor cells SI (605), the WTRU310 may be configured to send a measurement report or any other RRC message to the network requesting that a measurement interval be provided (615). Alternatively, when the WTRU310 reports neighboring cells to the network using existing measurement reports, (e.g., when the neighboring cell signal strength is above a certain threshold (610)), the WTRU310 may send an IE indicating that it needs a measurement interval (625) to read the neighboring cell SI. The IE may also be piggybacked as part of an existing RRC message.

Alternatively, or in addition, the WTRU310 may also report to the network in a measurement report or any other RRC message: the length of the measurement interval required to read the neighboring cell SI, and whether the WTRU310 requires one continuous interval or multiple smaller intervals. The WTRU310 may also specify the number of intervals it needs to read the CSG neighbor cell SI (625).

In one embodiment, a method of determining validity of a mapping from a PCI to a CGI is provided. Fig. 7 shows a flow diagram of a method 700 of determining a PCI-to-CGI mapping. The WTRU310 is configured to read a first set of SIs of neighboring CSG cells including a PCI or CGI (705). The WTRU310 may be configured to store a first set of SIs for neighboring CSG cells including a PCI (710). When the SI is read (705) and stored (710), the WTRU310 may be configured to start a timer (715). The timer may be started when the WTRU310 starts to acquire the SI of the neighboring CSG cell. The timer may be configured to indicate a period during which the PCI and CGI are continuously active. When the timer expires (720), the WTRU310 may be configured to read (i.e., retrieve) the SI of the second set of neighboring CSG cells (725). The WTRU310 may compare the first set of SIs and the second set of SIs to identify a CGI of the CSG cell (730). If the first set of SI matches the second set of SI, the WTRU310 explicitly identifies the CGI of the CSG cell (735). The validity timer may prevent the WTRU310 from reporting a wrong CGI to the network when reporting a cell for a particular PCI if the WTRU310 moves from one cell to another. Resolving PCI confusion means that the WTRU310 has explicitly identified the identity (CGI) of the CSG cell.

The WTRU310 may be required to know when or conditions that the PCI to CGI mapping is valid, and conditions that the WTRU310 is required to read the SI of the neighboring cell. The WTRU310 may move away from the neighboring CSG cell for which the CGI is read and encounter the same PCI in another CSG cell. In this case, the WTRU310 must read the neighboring cell SI again. The WTRU310 may determine whether it needs to re-read the neighboring cell SI, or a condition that the WTRU310 no longer considers the SI valid (which results in the clearing of the stored information of the associated PCI).

To make this determination, the WTRU310 may use the validity timer 720 as described above. The duration of the validity timer may be predefined or signaled by the network. Alternatively, the validity timer may be started upon transmission of a measurement report containing the relevant PCI and the associated CGI. Alternatively, the timer may be started when the WTRU310 stops detecting the relevant PCI. Alternatively, the timer may be stopped when it is determined that one of the following conditions is satisfied.

Therefore, once the validity timer expires or stops, the WTRU310 reads the neighboring SI again to determine the CGI. Alternatively, rather than the WTRU310 automatically re-reading, the WTRU310 may wait for an indication that the network re-reads the SI. The network may signal a common validity time period for all CSG cells, or the network may signal a validity timer for each CSG cell.

Alternatively, implicit rules may be defined requiring that whenever the WTRU310 performs a reselection procedure or selects a new Public Land Mobile Network (PLMN), the WTRU310 may be configured to read the SI of all neighboring cells to perform the PCI to CGI mapping. The WTRU310 may be configured to read the SI of all neighboring cells even if the WTRU310 has previously read the SI while in a previous cell or PLMN. Alternatively, once the WTRU310 performs reselection or PLMN selection, the network may signal a list of CSG neighbor cells that the WTRU310 should re-read to perform PCI to CSG mapping.

Fig. 8 shows a block diagram of a method 800 of determining the validity of a PCI-to-CGI mapping according to another embodiment. The WTRU310 is configured to read a first set of required SIs for neighboring CSG cells that include a PCI or CSG ID (805). The WTRU310 may be configured to store the obtained SI and PCI 810 for the neighboring CSG cells. The WTRU310 is configured to determine whether the mapping is considered valid. The WTRU310 may be configured to determine whether the serving cell has changed (i.e., an inter-cell handover has occurred) and whether the source or target cell is not using the relevant PCI (815). If the determination in step 815 is positive, the WTRU310 may be configured to re-read the second set of SIs (820). The WTRU310 is configured to compare the second set of SIs with the first set of SIs (825) to determine whether the PCI confusion is resolved (830). The WTRU310 is configured to send a message (i.e., a measurement report) to the network stating that the PCI confusion has been resolved (835).

Alternatively, the mapping may be considered invalid when the WTRU310 is configured to send a measurement report that no cell is using the PCI. This may occur when the WTRU310 moves away from the cell of interest. Alternatively, the mapping may be considered invalid when the WTRU310 may be configured to detect PCI collisions for PCIs, i.e., two different cells using the same PCI may be sensed at a significant level at a given location. The mapping is considered invalid when the WTRU310 is instructed to switch to a cell with an associated PCI but fails the switch, or fails because the WTRU310 is denied access. When the mapping is invalid, the WTRU310 may signal to the network that the mapping is invalid, or retry decoding the CGI the next time the PCI is measured, or retry decoding only when the network instructs the WTRU310 to perform reading the SI.

Alternatively, the network may signal the CSG neighbor cell in an SI or RRC message indicating that the CSG neighbor cell WTRU310 needs to re-read the CGI. The WTRU310 may be configured to read the SI of the signaled CSG cell based on the implicit conditions or timer values mentioned above with reference to fig. 7. For the remaining CSG cells, the WTRU310 may retain the PCI to CSG mapping.

Alternatively, the network may use an IE with the re-read CSG neighbor signaled in an RRC message or SI. When the IE exists, or is set to true, the WTRU310 may re-read the CSG neighbor cell SI to confirm the PCI to CGI mapping. The IE may be one common IE set for all CSG cells, or the network may signal one IE for each CSG cell.

Alternatively, the WTRU310 mapping between CGI and a predefined PCI (used by CSG cell or hybrid cell) is considered valid when a set of WTRU conditions or measurements match a set of conditions or measurements of CGI that have been previously measured (i.e., characteristics (finger), measured geographical location). The condition or measurement may be an identity of a serving macro cell or a neighboring macro cell. The mapping remains valid for a predefined or signaled duration, or until notification from the network, or until the WTRU310 determines that the mapping is no longer valid. For example, after a handover failure to a CSG cell matching the relevant feature occurs, and the CSG cell is considered as an allowed CSG (i.e., within an allowed range), the mapping is no longer valid.

Alternatively, when the WTRU310 moves out of the Location Area (LA) or Tracking Area (TA) or Routing Area (RA), the WTRU310 is triggered to measure the CSG or CGI of the neighboring cell or to consider the acquired information invalid, (i.e., a tracking area or location area update or routing area update or User Registration Area (URA) update has occurred). If the WTRU310 is in an idle state, or a CELL paging channel (CELL _ PCH)/URA _ PCH state, or a CELL forward channel (CELL _ FACH) state, the WTRU310 may measure all neighbors within the area. If the WTRU310 is in active mode, the WTRU310 measures the CGI and CSG if the quality of the neighboring cell is above a threshold for a configured amount of time or the network indicates that the WTRU310 should measure the channel.

When the quality of the neighboring CSG cell is below a threshold, the WTRU310 may consider the acquired SI of the neighboring CSG cell with the corresponding PCI invalid. Alternatively, the WTRU310 considers the SI invalid if the quality or signal level of the neighboring CSG cell is below a threshold within a configured or predefined period time. The quality corresponds to the common pilot channel per chip (CPICH) energy (Ec)/noise power spectral density (No) or Reference Signal Received Quality (RSRQ) of the UMTS or LTE system, respectively. The signal level corresponds to a CPICH Received Signal Code Power (RSCP) or a Reference Signal Received Power (RSRP) of a UMTS or LTE system, respectively. The threshold may be a network configured threshold or a WTRU determined threshold. The parameters may be configured by the network as a specific CSG threshold or by using an existing absolute threshold value configured for other intra-frequency or inter-frequency events. For example, an S-measurement or any other threshold may be used. When the measurements (reference signal received power (RSRP) or Reference Signal Received Quality (RSRQ)) are higher than S-measurements, the WTRU310 is not required to perform specific measurements. Alternatively, the WTRU310 may add an offset to any configured threshold to determine a new threshold for SI validity. Alternatively, the threshold may be determined by subtracting a predefined or signaled offset from the signal level or quality of the neighboring cell when the WTRU310 has started or ended the process of acquiring the SI of the neighboring cell.

The reduced quality or signal level of the neighboring cell may mean that the WTRU310 is leaving the neighboring CSG cell and the likelihood of encountering a different CSG cell with the same PCI coverage is increased. Alternatively, the quality or signal level of the neighboring cell is below the reporting range of any configured measurement events and rules.

In case the relevant neighboring cell triggers a measurement event (normal event or CSG specific event, e.g. a3 in LTE), the WTRU310 considers the SI invalid when the case of triggering the event is no longer true or the case exit case of the event becomes true. In other words, the neighboring cell is no longer a predefined offset over the serving cell. Event a3 may indicate that a neighboring cell becomes a predefined offset better than the serving cell.

The WTRU310 may consider the SI of the neighboring cell invalid after successfully sending a measurement report containing information obtained by acquiring the SI of the cell. In other words, after sending the measurement report including the CGI and other information to the network, the WTRU310 clears the information from memory or considers the information invalid.

The WTRU310 may consider the obtained SI of the neighboring cell invalid when leaving the characteristic area, or geographic area, where the measurement was triggered. In particular, upon reporting the out-of-proximity-area message to the network, the WTRU310 may clear the stored SI for the PCI that it has read (if any SI is stored). Alternatively, this may occur if the WTRU310 is leaving the current geographic area and entering a new geographic or feature area where the current PCI is not considered possible. For example, the PCI does not correspond to any one CSG stored in the whitelist according to the stored characteristic information.

If the network sends a message explicitly instructing the WTRU310 to acquire the SI of the PCI, the WTRU310 may clear the SI of the neighboring cell and reacquire the SI. The PCI corresponds to the PCI for which the WTRU310 stores SI. The message may be a measurement control or reconfiguration message.

The WTRU310 may consider the SI invalid when the network sends measurements to the WTRU310 to prevent inter-frequency or inter-RAT measurements. For example, the WTRU310 no longer has an inter-frequency or inter-RAT measurement configuration.

Alternatively, the WTRU310 may consider the SI invalid when changing RRC states, such as changing from idle to connected states, and vice versa. Alternatively, when a state transition occurs and the WTRU310 has stored this information, the WTRU310 may inherit and use the same information in the new state until determined to be invalid by one of the alternative embodiments defined above.

If the SI is considered invalid, and if a measurement report is triggered, the WTRU310 may null the SI report. Also, if the network wishes the WTRU310 to re-read the SI, the network may send additional explicit signaling as it did in the initial reading. Alternatively, the WTRU310 may clear the content and automatically reread the SI during the automatic gap without waiting for an explicit indication by the network. The solution is applicable to WTRUs in idle mode or connected mode.

In another embodiment, steps are provided for reporting the CGI to the source cell and requesting a gap. Various methods for reporting the identity of a CSG cell or hybrid cell whose PCI has been measured by the WTRU310 (900 and 1000) are described below (as shown in fig. 9 and 10). The methods may be used in combination. In general, reporting or other communications from the WTRU310 to the network may be performed using a measurement report message or any other message defined for this purpose or a new RRC message.

In a first approach, as shown in fig. 9, the WTRU310 is configured to read the PCI of the CSG cell (905). The WTRU310 is configured to identify a CGI corresponding to a measured PCI used by a CSG cell (910). The WTRU310 determines whether the validity of the mapping is true (915). The WTRU310 is configured to report, to the network (i.e., the source cell), the CGI corresponding to the measured PCI used by the CSG cell (as long as it has a valid mapping of CGIs for the measured PCI) (920). The WTRU310 reports that the CGI corresponds to an allowed CSG (920). The WTRU310 is configured to report to the network that the CGI of the measured PCI does not correspond to a CSG cell on a condition that the mapping is invalid (925).

Optionally, the WTRU310 only reports this information, and not the CGI, provided CSG is not allowed. Optionally, the WTRU310 does not report the CGI or any additional information, provided CSG is not allowed. Optionally, the WTRU310 also reports the time at which the mapping was determined. This information may be conveyed in a measurement report containing the PCI of the CSG cell or in any other RRC message.

Based on this information, the network may initiate a handover procedure to the CSG cell according to the received signal level of the CSG if the CSG is an allowed CSG. If the WTRU310 does not report the CGI of the measured PCI used by the CSG cell or hybrid cell, the network may instruct the WTRU310 to measure the CGI of the CSG cell and allocate the needed gaps to facilitate the measurement.

Another method is described for reporting CGIs including the possibility of allowed CSG cells to the network 1000, as shown in fig. 10. The WTRU310 is PCI aware and typically has 504 unique cell identities (i.e., PCIs) divided into 168 unique cell identity groups. The WTRU310 knows the range of PCIs reserved for closed cells (i.e., non-hybrid cells or open cells). Any PCI that is outside the closed cell range is within the hybrid cell range or the open cell range. The WTRU310 is configured to read the PCI of the CSG cell (1005). The WTRU310 determines whether the PCI corresponds to a hybrid cell (1010). If the WTRU310 detects that the PCI corresponds to a hybrid or open cell (based on the knowledge of the PCI range used by the hybrid or open cell), the WTRU310 knows that the cell is within the allowed range (1015). The WTRU310 is configured to report information to the network when it determines that the PCI is or may be used by an allowed CSG or hybrid cell (1020). If the cell is within range of the closed cell (1025), the WTRU310 reports information to the network indicating that the PCI is, or is highly likely to be, used by the non-allowed CSG cell (1030). The PCI may correspond to a closed cell of which the WTRU is a member.

The process of determining that the PCI is being used, or has a high likelihood of being used, by a non-allowed CSG cell may be based on the WTRU310 recognizing a set of conditions or measurements, such as features that exist when the WTRU310 is in the vicinity of an allowed CSG cell, an allowed hybrid cell, or a non-allowed CSG cell. For example, the set of conditions may include that the WTRU is geographically located around a predefined location and that the PCI of the cell matches the PCI of the last access allowed CSG cell usage. The report may be conveyed in any measurement report or any other RRC message that includes the PCI of the CSG cell. Alternatively, the WTRU310 is instructed to provide an identity of the CSG or hybrid cell, communicated in a measurement report as a result of a message received from the network. Or, if a condition indicating that the handover is to be performed urgently is satisfied, communicated in a transmitted measurement report.

For example, the report may be sent when the hybrid or CSG cell is detected to be above a received signal level, or after a timer started upon detection of the hybrid or CSG cell being above a particular received signal level expires or stops. The timer is stopped if the WTRU310 successfully decodes the hybrid cell or CSG cell identity. Due to the opportunity for DRX operation, the timer may be stopped and the WTRU310 may successfully decode the identity without the need for network allocation gaps. Alternatively, the timer is used only if the signal level from the serving, hybrid or CSG cell is such that handover to the hybrid or CSG cell is not urgent.

Examples of conditions for determining that a handover procedure is urgent include: the difference (which may be a negative number) between the signal level of the CSG or hybrid cell and the signal level of the serving cell in dB is above the threshold. The latter case is optionally used only if the serving macro cell and the target CSG cell or hybrid cell are at the same frequency.

The information may include an indication that the PCI may correspond to an allowed CSG cell, a hybrid cell, or a non-allowed CSG cell, and thus measurement of the CGI is necessary, or unnecessary. In case the indication indicates that the cell is allowed, the indication may be equivalent to requesting the network to allocate a gap to facilitate the measurement of CGI. Alternatively, the indication may be interpreted as an indication to the network that the WTRU310 may attempt or is attempting measurements for CGIs using idle time, and that allocation of gaps is necessary. In case the indication indicates that the cell is not allowed, such indication is equivalent to requesting the network not to allocate a gap to facilitate the measurement of CGIs, or a notification that the cell is not allowed, or the measurement of CGIs cannot be attempted. Optionally, the information is sent only if the WTRU310 does not have a CGI valid mapping for the measured PCI. Alternatively, the silent indication may mean that the PCI may correspond to an allowed CSG cell or a hybrid cell. Alternatively, no indication implies that the measurement of CGI is not necessary.

The information may include an assumed or measured CGI of a CSG cell or hybrid cell using the PCI (if available). This may be reported along with an indication of whether CSG is allowed. Optionally, the WTRU310 may only report the information, and not the CGI, provided that CSG is not allowed. Optionally, there may be an indication that the mapping between PCI and CGI has been determined or whether CGI was just measured. Optionally, the information is only reported when the mapping between CGI and PCI remains valid. Optionally, reporting is only done when the WTRU310 does not know any PCI confusion, whereby the PCI of the allowed CSG is also used by another CSG near the source cell.

In case the CGI is provided, the network may initiate a handover procedure to the CSG cell according to the received CSG signal level. For example, the WTRU310 may indicate that the measured PCI corresponds to an allowed CSG. If the WTRU310 only reports an indication that the PCI may correspond to an allowed CSG cell or hybrid cell, the network may instruct the WTRU310 to measure the CGI of the CSG cell or hybrid cell and/or allocate the required gaps to facilitate the measurement. The network may indicate the PCI of the cell whose CGI needs to be measured so that in the case where there are multiple PCIs, the WTRU310 knows which PCI needs to be measured. If the network knows that the PCI corresponds to a hybrid cell that is always allowed, the network may command the WTRU310 to measure the identity of the hybrid cell even if the WTRU310 does not provide the indication. The gap allocation may be indicated in the reconfiguration message or in the measurement control message.

Alternatively, the network may only allocate a gap after a condition indicating that the execution of the handover is urgent is satisfied. For example, the assignment may be performed upon expiration of a timer that is turned on upon receipt of a message from the WTRU310 indicating that the detected PCI may correspond to an allowed CSG cell or a hybrid cell. The timer may stop upon receiving a WTRU message containing an identity of a CSG cell or a hybrid cell. This procedure may utilize the normal timing due to DRX operation to set aside a period of time for the WTRU310 to decode the identity of the CSG cell, thus avoiding unnecessary gap configurations.

Other examples of conditions for determining that a handover procedure is urgent include: the difference (which may be a negative number) between the signal level of the CSG or hybrid cell and the signal level of the serving cell in dB is above the threshold. The latter case is optionally used only if the serving macro cell and the target CSG cell or hybrid cell are at the same frequency.

In case the WTRU310 only reports an indication that the PCI may correspond to a non-allowed CSG cell, the network may refrain from ordering the WTRU310 to measure the CGI of the CSG cell and refrain from performing any mobility procedures towards the CSG cell.

The WTRU310 may attempt to make measurements of CGI during idle time provided by DRX operation and/or measurement gaps before or after it is being allocated gaps. The WTRU310 may initiate measurements when the PCI of a CSG cell or a hybrid cell is detected. The WTRU310 may initiate the measurement when the PCI of a CSG cell or hybrid cell is detected that has a received signal strength or quality above a certain threshold. The WTRU310 may initiate the measurement when the difference between the signal level of the CSG cell or hybrid cell in dB and the signal level of the serving cell is above a threshold. The WTRU310 may initiate the measurement upon expiration of a timer that is turned on upon detection of a PCI of a CSG cell or a hybrid cell having a received signal strength or quality above a certain threshold. If the signal strength or quality is below a threshold, the timer is stopped. The WTRU310 may initiate the measurement after sending a measurement report containing the PCI of the CSG or hybrid cell. Alternatively, the WTRU310 may initiate the measurement after sending a measurement report that includes the PCI of the CSG cell or hybrid cell and indicates that the PCI may correspond to an allowed CSG cell or hybrid cell.

To support triggering of measurement reports in any of the above methods, a new measurement event may be defined. The definition of different events facilitates the use of different thresholds for neighboring CSG cells; or a hybrid cell as opposed to a standard cell. Examples of these new events are described below. The event marker names described herein are arbitrary: events H3, H4, H5, and H6 are described.

Event H3 occurs when a CSG cell or a hybrid cell neighbor becomes better than an offset of the serving cell. The event is similar to event a3 in the RRC protocol of LTE, but with the additional condition that the neighboring cell is a CSG cell, a hybrid cell, or is identified by the WTRU310 as a potential allowed CSG cell or hybrid cell.

Event H4 occurs when a CSG cell or a hybrid cell neighbor becomes better than a predefined threshold. The event is similar to event a4, but with the additional condition that the neighboring cell is a CSG cell, a hybrid cell, or is identified by the WTRU310 as a potential allowed CSG or hybrid cell.

The event occurs H5 when the service is worse than the predefined threshold 1 and the CSG cell or hybrid cell neighbor is better than the predefined threshold 2. The event is similar to event a5 with the additional condition being that the neighboring cell is a CSG cell, a hybrid cell, or identified by the WTRU310 as a potential allowed CSG or hybrid cell.

Event H6 occurs when the identities of neighboring CSG cells or hybrid cells have been successfully measured.

Figure 11 shows a method 1100 of receiving signaling in a WTRU310 to start reading SI of neighboring CSG cells and allocating reception resources in the WTRU. The WTRU310 is configured to receive a signal to read the SI of at least one neighboring CSG cell (1101). The signal may have been generated by the network in response to expiration of a timer or signaled due to an event, such as a threshold crossing point, where a signal strength of the serving cell or the hybrid cell exceeding or falling below a monitoring threshold indicates that a handover is unnecessary or alternatively desirable. The WTRU310 is configured to receive an allocation of DRX gaps (1103) that facilitate measurement of SI from neighboring CSG cells. The WTRU310 is configured to read SI from a neighboring CSG cell during an allocated DRX gap (1105). When having read the SI of the neighboring CSG cell, the WTRU310 is configured to send a measurement report to the network containing the SI of the neighboring CSG cell (1107).

In one example, a procedure is provided for a WTRU to handover to an allowed CSG cell. The WTRU310 is initially served by a macro cell. The WTRU310 is configured to detect the PCI of the CSG cell. The characteristics of the CSG cell match those of previously allowed CSG cells. The characteristic may be a geographical location or a PCI used by the CSG cell. However, the WTRU310 does not have a valid CSG ID for the cell. The WTRU310 may attempt to decode the CSG ID during DRX generated idle periods and/or measurement gaps. The WTRU310 may send a measurement report to the network that includes an indication that the PCI and CGI of the CSG cell require measurement. After a predefined delay, the network sends a message allocating gaps to the WTRU310 to facilitate the measurement of CGI. The WTRU310 successfully decodes the CGI and finds that the CSG is included on its list of allowed CSGs. The WTRU310 sends a measurement report including the PCI and the corresponding CGI. The network initiates a handover procedure to the CSG cell.

In another example, a procedure for a WTRU to measure a non-allowed CSG cell is provided. The WTRU310 is initially served by a macro cell. The WTRU310 detects the PCI of the CSG cell. The characteristics of the CSG cell match those of previously allowed CSG cells. The characteristic may be a geographical location or a PCI used by the CSG cell. However, the WTRU310 does not have a valid CSG ID for the cell. The WTRU310 may attempt to decode the CSG ID during DRX generated idle periods and/or measurement gaps. The WTRU310 may send a measurement report to the network that includes an indication that the PCI and CGI of the CSG cell require measurement. After a predefined delay, the network sends a message allocating gaps to the WTRU310 to facilitate the measurement of CGI. The WTRU310 may decode the CGI and find that the CSG is not included on its list of allowed CSGs. The WTRU310 sends a measurement report including the PCI and does not send any indication that the CGI needs to make measurements. The network knows that the PCI does not correspond to an allowed CSG cell and does not initiate a handover procedure to the CSG cell.

When the network allocates a gap to help the WTRU310 measure the identity of the CSG cell or the hybrid cell, the gap may be allocated as described below.

A single or limited number of instances of gaps (instances) are predefined in time. The gap is not repeated outside of this number of instances. The gap may be defined in terms of a subframe interval reference starting System Frame Number (SFN) and a subframe number. If there is more than one gap instance, the time interval between instances may also be indicated or predefined.

An interval or series of intervals occurs on a periodic basis with predefined or signaled intervals between them. The interval will be allocated until one or a combination of the following events occur: the WTRU310 sends a measurement report, the WTRU310 sends a measurement report with an identity of a CSG cell or a hybrid cell, the WTRU310 sends a measurement report indicating that the identity of the CSG cell or the hybrid cell cannot be measured or need not be measured (e.g., if the WTRU310 does not desire to access the CSG cell or the hybrid cell), the WTRU310 sends a measurement report indicating that the signal strength of the CSG cell or the hybrid cell is below a threshold, the WTRU310 switches to a new cell (i.e., the CSG cell or any other cell), the WTRU310 receives a new measurement control or other RRC message from the network indicating that a gap is stopped, or a gap is allocated at the expiration of a timer that is turned on upon receiving the message allocating the gap. The timer duration has been indicated in the message.

A WTRU cross for measuring CGI during gaps is providedThe method of (1). Based on the CSG neighbor cell signal quality, it may take a significant amount of time to decode the Master Information Block (MIB), and then decode the SIBs of the neighbor cells₁. To reduce this problem, the following methods may be used alone or in combination.

For reading MIB and SIB₁A plurality of gaps are defined. In other words, the WTRU310 may be configured to detect and decode the MIB in a first gap and detect and decode SIBs in a second gap₁. The two gaps may individually be smaller than a single gap that performs both operations. This is advantageous in minimizing the corruption of data transfers.

Alternatively, reading only the MIB or reading only the SIB may also be used₁Defining a plurality of gaps. The WTRU310 may combine hybrid automatic repeat request (HARQ) transmissions received from two different gaps. This requires reservation of one or more HARQ processes. The HARQ process may not be used during the intervening data transmission. The reserved HARQ processes may be signaled by the network when a gap is configured. Alternatively, there may be predefined HARQ processes that are used all the time when necessary. In either case, the WTRU310 flushes the corresponding HARQ buffer at the beginning of reception during the first gap.

A network-based approach to resolving PCI confusion is provided. To allow a network-based approach to resolve PCI, the network may decide to resolve the PCI confusion if the network realizes that the serving cell signal strength is not good enough and the handover procedure cannot be delayed. If the network cannot resolve the PCI confusion, it may request the WTRU310 to read the SI of the neighboring cell, or it may directly handover the WTRU310 to the neighboring cell.

In a handover command sent by the network, or in any other RRC message (i.e., measurement control, etc.), the network may set an IE that may indicate whether the WTRU310 may read the SI of the CSG neighbor cell. Alternatively, the presence of an IE may indicate that the WTRU310 is required to read the SI of the neighboring cell, while the absence of an IE indicates that the WTRU310 is not required to read the SI of the neighboring cell.

If the WTRU310 is required to read the SI of the CSG neighbor cell, the WTRU310 may start this procedure and once it finishes reading the SI, it may inform the network that the SI has been obtained through a measurement report or any other RRC message. The network may take appropriate action, such as sending data to neighboring cells.

Figure 12 is a block diagram example 1200 of a WTRU310 configured to receive cell broadcasts and read neighboring CSG cells. The WTRU310 includes an antenna 1205, a transmitter 1210, a receiver 1215, a processor 1220, and a Universal Subscriber Identity Module (USIM) (or LTE equivalent) 1225. The receiver 1215 is configured to receive broadcasts from cells including cell IDs via the antenna 1205. The processor 1220 is electrically connected to the transmitter 1210, the receiver 1215, and the USIM (or LTE equivalent) 1225. The processor 1220 is configured to perform the method for inbound handover to a CSG cell described above.

Although the features and elements of the present invention are described in the particular combinations, each feature or element can be used alone without the other features and elements or in various combinations with or without other features and elements. The methods or flow charts provided herein may be implemented in a computer program, software, or firmware tangibly embodied in a computer-readable storage medium for execution by a general purpose computer or a processor. Examples of the computer-readable storage medium include Read Only Memory (ROM), Random Access Memory (RAM), registers, buffer memory, semiconductor memory devices, magnetic media such as internal hard disks and removable disks, magneto-optical media, and optical media such as CD-ROM disks and Digital Versatile Disks (DVDs).

For example, suitable processors include: a general-purpose processor, a special-purpose processor, a conventional processor, a Digital Signal Processor (DSP), a plurality of microprocessors, one or more microprocessors in association with a DSP core, a controller, a microcontroller, an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA) circuit, any Integrated Circuit (IC), and/or a state machine.

Examples

1. A method implemented in a wireless transmit/receive unit (WTRU), the method comprising:

reading a first set of system information of neighboring Closed Subscriber Group (CSG) cells, the first set of system information including a Cell Global Identity (CGI) and a Physical Cell Identity (PCI).

2. The method of embodiment 1, further comprising:

storing a first set of system information;

starting a timer; and

reading a second set of system information of neighboring CSG cells if the timer has expired.

3. The method of embodiment 2, further comprising:

in the case where the second set of system information is the same as the first set of system information, then CGIs of neighboring CSG cells are identified.

4. The method as in any one of embodiments 1-3, further comprising:

a message is transmitted to the network indicating that the PCI confusion has been resolved.

5. The method of embodiment 4 wherein the message includes PCIs of neighboring CSG cells.

6. The method according to one of embodiments 4-5, wherein the message includes CGIs of neighboring CSG cells.

7. The method as in any one of embodiments 1-6, further comprising:

automatically determining a gap duration required to read the first set of system information and the second set of system information based on a channel reception quality of a signal from the neighboring CSG cell; and

the required gap duration is signaled to the network.

8. The method as in any one of embodiments 1-7 wherein the signal strength and signal quality of the current serving cell is monitored for comparison to a predefined threshold.

9. The method of embodiment 8 wherein system information of neighboring CSG cells is read in case the signal strength and signal quality of the current serving cell is below predefined thresholds.

10. A wireless transmit/receive unit (WTRU), comprising:

a processor configured to read a first set of system information of neighboring Closed Subscriber Group (CSG) cells, the first set of system information including a Cell Global Identity (CGI) and a Physical Cell Identity (PCI).

11. The WTRU of embodiment 10, further comprising:

the method includes storing a first set of system information, starting a timer, and reading a second set of system information of neighboring CSG cells if the timer has expired.

12. The WTRU of embodiment 11, further comprising:

in the case where the second set of system information is the same as the first set of system information, CGIs of neighboring CSG cells are identified.

13. The WTRU as in any one of embodiments 10-12 further comprising:

a transmitter configured to transmit a message to a network indicating that the PCI confusion has been resolved.

14. The WTRU of embodiment 13 wherein the message includes PCIs of neighboring CSG cells.

15. The WTRU as in any one of embodiments 13-14 wherein the message includes CGIs of neighboring CSG cells.

16. The WTRU as in any one of embodiments 10-15 further comprising:

a processor configured to automatically determine a gap duration required to read the first set of system information and the second set of system information based on a channel reception quality of a signal from the neighboring CSG cell; and

a transmitter configured to signal the required gap duration to the network.

17. The WTRU as in any one of embodiments 10-16 wherein signal strength and signal quality of a current serving cell are monitored for comparison to a predefined threshold.

18. The WTRU of embodiment 17 wherein system information of neighboring CSG cells is read on a condition that a signal strength and a signal quality of a current serving cell are below predefined thresholds.

19. A method implemented in a wireless transmit/receive unit (WTRU), the method comprising:

reading a Physical Cell Identity (PCI) of a neighboring Closed Subscriber Group (CSG) cell.

20. The method of embodiment 19, further comprising:

determining whether the PCI corresponds to a predefined mixed cell range; and

in the case where the PCI corresponds to a predefined mixed cell range, the neighboring CSG cells are within an allowed open cell range.

21. The method as in any one of embodiments 19-20, further comprising:

reporting information indicating that the PCI is used by the neighboring CSG cell to a network.

22. The method of embodiment 20 wherein the neighboring CSG cell is within a closed cell range in the event that the PCI does not correspond to a predefined mixed cell range.

23. The method of embodiment 20 wherein in the event that a neighboring CSG cell is within closed cell range, reporting information to the network indicating that the PCI is highly likely to be used by CSG cells within closed cell range.

A processor in association with software may be used to implement a radio frequency transceiver for use in a Wireless Transmit Receive Unit (WTRU), User Equipment (UE), terminal, base station, Radio Network Controller (RNC), or any host computer. The WTRU may be used in conjunction with modules, implemented in hardware and/or software, such as a camera, a video camera module, a video phone, a speakerphone, a vibration device, a speaker, a microphone, a television transceiver, a hands free headset, a keyboard, and BluetoothA module, a Frequency Modulation (FM) radio unit, a Liquid Crystal Display (LCD) display unit, an Organic Light Emitting Diode (OLED) display unit, a digital music player, a media player, a video game player module, an internet browser, and/or any Wireless Local Area Network (WLAN) or Ultra Wideband (UWB) module.

Claims (17)

1. A method implemented in a wireless transmit/receive unit (WTRU), the method comprising:

reading a first set of system information of neighboring Closed Subscriber Group (CSG) cells, the first set of system information comprising a Cell Global Identity (CGI) and a Physical Cell Identity (PCI);

storing the first set of system information;

starting a timer;

reading a second set of system information of the neighboring CSG cell if the timer has expired; and

identifying the CGI of the neighboring CSG cell if the second set of system information is the same as the first set of system information.

2. The method of claim 1, further comprising:

a message is transmitted to the network indicating that the PCI confusion has been resolved.

3. The method of claim 2, wherein the message includes a PCI of the neighboring CSG cell.

4. The method of claim 2, wherein the message comprises CGIs of the neighboring CSG cell.

5. The method of claim 1, further comprising:

automatically determining a gap duration required to read the first set of system information and the second set of system information based on a channel reception quality of a signal from the neighboring CSG cell; and

the required gap duration is signaled to the network.

6. The method of claim 1, wherein the signal strength and signal quality of the current serving cell is monitored for comparison to a predefined threshold.

7. The method of claim 6, wherein system information of the neighboring CSG cell is read if the signal strength and signal quality of the current serving cell are below the predefined thresholds.

8. A wireless transmit/receive unit (WTRU), comprising:

a processor configured to:

reading a first set of system information of neighboring Closed Subscriber Group (CSG) cells, the first set of system information comprising a Cell Global Identity (CGI) and a Physical Cell Identity (PCI);

storing the first set of system information;

starting a timer;

reading a second set of system information of the neighboring CSG cell if the timer has expired; and

identifying the CGI of the neighboring CSG cell if the second set of system information is the same as the first set of system information.

9. The WTRU of claim 8, further comprising:

a transmitter configured to transmit a message to a network indicating that the PCI confusion has been resolved.

10. The WTRU of claim 9, wherein the message includes a PCI of the neighboring CSG cell.

11. The WTRU of claim 9 wherein the message includes CGIs of the neighboring CSG cell.

12. The WTRU of claim 8, further comprising:

a processor configured to automatically determine a gap duration required to read the first set of system information and the second set of system information based on a channel reception quality of a signal from the neighboring CSG cell; and

a transmitter configured to signal the required gap duration to the network.

13. The WTRU of claim 8 wherein signal strength and signal quality of a current serving cell are monitored for comparison to predefined thresholds.

14. The WTRU of claim 13 wherein system information of the neighboring CSG cell is read on a condition that a signal strength and a signal quality of the current serving cell are below the predefined threshold.

15. A method implemented in a wireless transmit/receive unit (WTRU), the method comprising:

reading a Physical Cell Identity (PCI) of a neighboring Closed Subscriber Group (CSG) cell;

determining whether the PCI corresponds to a predefined mixed cell range;

in the case that the PCI corresponds to the predefined mixed cell range, the neighboring CSG cell is within an allowed open cell range;

reporting information indicating that the PCI is used by the neighboring CSG cell to a network.

16. The method of claim 11, wherein the neighboring CSG cell is within a closed cell range on a condition that the PCI does not correspond to the predefined mixed cell range.

17. The method of claim 12, wherein in the event that the neighboring CSG cell is within closed cell range, reporting information to a network indicating that the PCI is highly likely to be used by CSG cells within closed cell range.