HK1151412A

HK1151412A - Method and apparatus for searching for closed subscriber group cells

Info

Publication number: HK1151412A
Application number: HK11105555.3A
Authority: HK
Inventors: S‧索马桑德朗; R‧P‧穆克吉; M‧萨摩尔; J‧L‧格鲁
Original assignee: 交互数字专利控股公司
Priority date: 2008-03-21
Filing date: 2009-03-20
Publication date: 2012-01-27

Description

Method and apparatus for searching closed subscriber group cells

Technical Field

The present application relates to wireless communications.

Background

Current work on the third generation partnership project (3GPP) Long Term Evolution (LTE) system is primarily directed to updating the technology, architecture, and methodology under new LTE settings and configurations. These efforts to achieve faster user data rates and richer applications and services at less cost will improve spectral efficiency, reduce time delay, and improve radio resource utilization.

As part of these efforts, 3GPP proposed the introduction of the concept of a local evolved node b (HeNB) in LTE systems, and in response thereto, HeNB may also be introduced in release 8 Wideband Code Division Multiple Access (WCDMA), global system for mobile communications (GSM) enhanced data rates for GSM evolution (EDGE) radio access network (GERAN), and other cellular communication (cellular) standards. Henbs refer to physical devices that may be similar to Wireless Local Area Network (WLAN) Access Points (APs) that may be designed in a manner that allows access to cellular communication services for users within a very small service range, such as a home or small office. This is particularly useful for areas where cellular communication networks are not yet deployed and/or where traditional RAT coverage already exists, as well as areas where cellular communication coverage may be weak or non-existent for radio related reasons, such as subway or shopping centers. A subscriber (e.g., an individual or an organization) may deploy an HeNB in an area where such service is needed.

The HeNB is intended to connect to the operator's core network by using a public internet connection, which may be implemented by e.g. Digital Subscriber Line (DSL), which is freely available in e.g. homes and shops throughout the country. This is particularly useful for areas where LTE has not been deployed and/or where legacy 3GPP Radio Access Technology (RAT) coverage already exists. This is also particularly useful for areas where LTE coverage may be weak or non-existent due to radio transmission problems occurring in places such as subway or shopping malls. A cell, which is a radio coverage area provided by an HeNB deployed by the HeNB, may be accessed only by a set of subscribers, called "homes", that have access to the services of the cell, and such a cell may be called an HeNB cell, or more generally, a Closed Subscriber Group (CSG) cell. An HeNB may be used to deploy one or more CSG cells over an area where LTE coverage is desired. CSG cells are deployed by henbs for LTE services or by home node bs (hnbs) for WCDMA or other legacy 3GPP RAT systems. A WTRU subscriber (associated with an individual or organization) may use an HeNB to deploy CSG cells (listed on a white list accessible to the WTRU subscriber) on an area where LTE service is desired. On the other hand, any non-barred WTRU may access the macro cell.

It has been proposed to indicate that a wireless transmit/receive unit (WTRU) as part of its whitelist configuration is also configured with the physical layer cell identifier (PCID) of the CSG cell it has accessed. These PCIDs may correspond to any combination of primary synchronization channels (P-SCHs) and secondary synchronization channels (S-SCHs) or some other form of physical layer (PHY) identification of CSG cells. It is also proposed that the WTRU be able to request that it allocate a measurement/cell search gap for itself for CSG cell measurement/search, where the request may be triggered by manual CSG cell search initiation. The measurement gap represents a point in time at which the WTRU adjusts away (tune away) from the serving cell so that the WTRU can search for a suitable CSG cell in the vicinity.

Currently, there have been proposals to indicate that a WTRU reads a Master Information Block (MIB) and a System Information Block (SIB) of a CSG cell in connected mode to decide whether an upper layer identity of the CSG cell (e.g., a generic cell identity of the CSG cell) is part of its white list. In addition, it is also noted that the WTRU may autonomously adjust away to create its own measurement gaps, allowing it to read SIBs of neighboring CSG cells.

However, there are still some problems to be solved. For example, no research has been made to understand under what conditions a WTRU should choose to autonomously tune away from the serving cell and read the CSG cell SIB. In addition, it is not clear whether the WTRU generates a continuous or a disjoint measurement gap, and whether the WTRU needs to send any indication when it autonomously adjusts away from its serving evolved node b (enb) or cell. In addition, it is not clear whether the WTRU should report to the network that it has detected a CSG cell or whether it has read and confirmed the upper layer identity.

While various attempted solutions have been proposed for active mode mobility between LTE macro cells and CSG cells, no comprehensive solution has emerged that can incorporate different types of mobility. Thus, there is a need for a process that can solve the above problems, bearing in mind the limitations imposed by standardized bodies. Accordingly, it would be beneficial to provide a method and apparatus for providing HeNB services to WTRUs.

A method and apparatus are presented for providing a WTRU with a mechanism to measure and report CSG cells. In particular, mechanisms are proposed that allow a WTRU to minimize the time required to identify a CSG cell that the WTRU has access to.

Disclosure of Invention

A method and apparatus for searching for CSG cells is described. The WTRU transmits a measurement/cell-search gap request message to the network of CSG cells including a cause value having at least one bit indicating whether transmission of the measurement/cell-search gap request message is due to a manual cell search instruction or a WTRU autonomous determination. The WTRU receives a measurement/cell-search gap allocation message from a network in response to the measurement/cell-search request message. The WTRU may also determine whether the WTRU has a Discontinuous Reception (DRX) gap long enough to read the MIB and SIBs of the neighboring CSG cell. If the DRX gap is not long enough, the WTRU may transmit a measurement/cell-search gap request message to the network or autonomously adjust away from the cell currently serving the WTRU to read the MIB and SIBs.

Preferably, the WTRU is configured with frequency information of a CSG cell that the WTRU has accessed and stores the frequency information in a memory such as a Universal Integrated Circuit Card (UICC), Universal Subscriber Identity Module (USIM) or in the WTRU. The frequency information may be configured in the WTRU using the same message that configures the WTRU with a whitelist of CSG IDs (identifiers), e.g., CSG Tracking Area (TA) IDs, corresponding to CSG cells that the WTRU has access to, or in a separate message. The frequency information may be a frequency band in which the CSG cell is deployed. Additionally, or alternatively, the frequency information may be a center frequency of the CSG cell with which the WTRU receiver is to synchronize.

The WTRU may be configured with the PCID of the CSG cell that the WTRU has access to using the same message that the WTRU is configured with the CSG identifier white list or in a separate message. Procedures for requesting measurement/cell-search gaps and handover assignments by a WTRU are disclosed, as well as procedures for handling measurement/cell-search gap assignments or handover assignment preference (replasal) for WTRUs in active and idle modes.

Drawings

A more detailed understanding of the present invention may be derived from the following detailed description taken in conjunction with the accompanying drawings by way of example:

figure 1 shows a wireless communication system including a WTRU and a network including a plurality of CSG cells and a plurality of macro cells;

figure 2 is an exemplary block diagram of a WTRU used in the wireless communication system shown in figure 1;

fig. 3-5 are flow diagrams of various processes for searching for CSG cells.

Detailed Description

As described below, the term "wireless transmit/receive unit (WTRU)" 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.

As described below, the term "base station" includes, but is not limited to, a node B, a site controller, an Access Point (AP), or any other type of interfacing device capable of operating in a wireless environment.

As described below, the term "Closed Subscriber Group (CSG) cell" includes, but is not limited to, a HeNB or HNB.

Although the description herein refers to LTE CSG cells, it is also applicable to CSG cells in any RAT network including, for example, WCDMA and GERAN communication systems.

Active mode mobility

Figure 1 shows a wireless communication system 10 including a WTRU100 and a network 105, the network 105 includingMultiple CSG cells (110)₁、110₂And 110₃) And a plurality of macro cells (115)₁And 115₂). CSG cell (110)₁、110₂And 110₃) With a PCID that may correspond to any combination of P-SCH 120 and S-SCH 125.

Fig. 2 is an exemplary block diagram of a WTRU100 for use in the wireless communication system 10. The WTRU100 includes an antenna 205, a receiver 210, a processor 215, a transmitter 220, and a memory 225. The memory 225 may include a CSG cell whitelist 230 and macrocell parameters 235. Alternatively, the WTRU100 may access the CSG cell whitelist 230 from an external resource such as the network 105 and/or at least one CSG cell 110 therein.

The request for measurement/cell-search gaps to be allocated to the WTRU100 for CSG cell measurement/search may be made by pairing existing neighboring CSG cells (110) by using neighboring cell relations or Global Positioning System (GPS), or by using some other algorithm₁、110₂And 110₃) The WTRU100 making the autonomous determination triggers. The request for measurement/search gaps may include a cause value for a request such as a manual cell search instruction or a WTRU-autonomous search request.

The message requesting a measurement/search gap may have a one-bit indicator for indicating to the network 105 including the at least one CSG cell 110 whether the request is due to a manual cell search instruction or a WTRU autonomous determination. The request for measurement/search gaps may be carried in a dedicated Radio Resource Control (RRC) message, or as part of any other RRC message, such as a measurement report. Alternatively, the request may be carried in a new RRC message (i.e., RRC event notification message) to report various WTRU-related events including, but not limited to, CSG manual search initiation, Mobile Originated (MO) voice call, and MO voice call in the Circuit Switched (CS) domain. The requests for the measurement gap and the cell search gap may be indicated separately using different messages or using a single message.

Additionally, or alternatively, the request for measurement/cell-search gaps may contain an indication as to whether the request is the first request or a subsequent (follow-up) request for a new cycle of measurement/cell-search gaps. The reason for such a subsequent request may be to verify the upper layer identity of the CSG cell 110 or to request a second gap to be allocated to the WTRU 100.

Upon receiving a request for measurement/cell-search gap allocation, the network 105 may allocate a first measurement/search gap, wherein the request may include a first request indication by setting a bit. The WTRU100 may be configured to then use the measurement/cell-search gap to attempt and search for a suitable CSG cell 110 in the vicinity. The WTRU100 may be configured to search for a specific PCID corresponding to the CSG cell 110 it has access to. In particular, the WTRU100 may be configured to search for a PCID corresponding to a CSG cell 110 in its CSG cell whitelist 230. The WTRU100 may be configured to focus its search on a particular frequency band and/or center frequency. The frequency and PCID information may be configured in the WTRU100 or may be indicated to the WTRU100 by the network 105 in its measurement/cell-search gap assignment message. The WTRU100 may be configured to obtain a cell upper layer identity, such as a CSG ID or CSG TA ID, carried on a Downlink (DL) broadcast channel. The WTRU100 may be configured to do so only for those cells whose PCID and/or frequency information matches the PCID and/or frequency information configured for the CSG cell whitelist 230 to which the WTRU100 has access. The WTRU100 may be configured to make measurements, such as Reference Signal Received Power (RSRP), on a particular cell it detects. The WTRU100 may be configured to do so only for those cells whose PCID and/or frequency information matches the PCID and/or frequency information configured for the CSG cell whitelist 230 to which the WTRU100 has access.

The WTRU100 may be configured to request another measurement/cell-search gap. The request may include an indication (e.g., via a bit) of a subsequent request. Any request for a measurement/cell-search gap may contain a bit indicating whether this is a first request or a subsequent (i.e. second) request. The WTRU100 may be configured to send the subsequent request when at least one of the following conditions is met:

1) if the WTRU100 determines that it has detected a cell whose frequency information and/or PCID matches the frequency information and/or PCID of the CSG cell 110 on its CSG cell whitelist 230. The determination may have been made in a previous measurement/cell-search gap.

2) If the WTRU100 needs a gap to acquire broadcast information (e.g., MIB or SIB) of a particular CSG cell 110 for the purpose of explicitly identifying the particular CSG cell as one that it has access to and belongs to its CSG cell whitelist 230.

3) If the measurements are made on detected cells that meet or exceed a predetermined criterion. These measurements may be made only for detected cells whose frequency information and/or PCID matches the frequency information and/or PCID of the CSG cell 110 on the CSG cell white list 230 of the WTRU 100.

4) If the WTRU100 needs a gap to measure the detected cell. The criteria may be invoked only if measurements are to be made for cells whose frequency information and/or PCID matches the frequency information and/or PCID of the CSG cell 110 on the CSG cell whitelist 230 of the WTRU 100.

5) If the WTRU100 has not completed detecting all cells in the band/center frequency that may include the CSG cell 110 it has accessed.

6) If the WTRU100 detects PCID collision between detected cells. This may only apply if at least two cells that detected a collision have the same frequency information as the CSG cell 110 on the CSG cell whitelist 230 of the WTRU 100. Additionally, or alternatively, this may only apply if a conflicting PCID is detected matching a CSG cell 110 on the CSG cell whitelist 230 of the WTRU 100. The collision determination may have been made in a previous measurement/cell-search gap.

The WTRU100 may be configured to embody the above conditions in its request to the network 105. The WTRU100 may be configured to keep requesting measurement/search gaps until it is finished performing some or all of the above-described procedures. In particular, the WTRU100 may be configured to indicate to the network 105 whether a collision of PCIDs is observed and optionally a scale (scale) of the detected collision, such as the same PCID that matches the PCID of the CSG cell 110 in the CSG cell whitelist 230. If the WTRU100 uses the PCID in its search for CSG cells 100 and the WTRU100 has completed detecting all cells available on the band/center frequency that may include the CSG cell 110 it has accessed, and the WTRU100 does not detect the PCID of the CSG cell 110 configured in its CSG cell white list 230 in the first search round, the WTRU100 may stop the current cycle of measurement/cell-search gap allocation request without requesting another measurement/cell-search gap. If the WTRU100 stops the current cycle of CSG cell search and if the current cycle is initiated by a manual cell search instruction, the WTRU100 may indicate to the user that no CSG cell 110 to which the user has subscribed has been detected, such as by way of an application. If the WTRU100 stops the current cycle of CSG cell search and the current cycle is initiated by WTRU autonomous detection of CSG cells 110 in the vicinity of the WTRU100, the WTRU100 may choose not to search/evaluate the conditions for searching for CSG cells 110 for at least a predetermined period of time. After the predetermined period of time has elapsed, the WTRU100 may again evaluate the conditions (e.g., using GPS coordinates or surrounding cells and/or TA IDs) that triggered the autonomous CSG cell search. The value of the predetermined time period may change (e.g., may increase) each time the WTRU autonomously fails a CSG cell search. The length of the predetermined period of time may be configured by the network 105.

If the WTRU100 sends another request for measurement/cell-search gap allocation, which may optionally include a subsequent request indication, the network 105 may configure the WTRU100 using another measurement/cell-search gap. The gap may be longer than the first gap. During this gap, the WTRU100 may perform measurements, such as RSRP measurements, on PCIDs detected earlier. During this gap, the WTRU100 may acquire cell broadcast information, such as SIBs and MIBs, using the PCID detected earlier. Optionally, the WTRU100 may be configured to measure only those cells whose PCID and/or frequency information match the PCID and/or frequency information of the CSG cell 110 configured in its CSG cell whitelist 230. Alternatively, the WTRU100 may be configured to acquire broadcast information for only those cells whose PCID and/or frequency information matches the PCID and/or frequency information of the CSG cell 110 in its CSG whitelist 230. Additionally, or alternatively, the WTRU100 may be configured to acquire broadcast information only for those cells whose measurements (e.g., RSRP) meet certain criteria. Once the broadcast information is obtained, the WTRU100 then makes a final determination of whether it has access to the CSG cell 110, preferably by, for example, matching the broadcast CSG identifier with the broadcast CSG identifier in its CSG cell whitelist 230. Alternatively, a new ID may be defined that is smaller than TA, which may be signaled on the MIB or SIB. The new ID may be derived from the TA or cell ID. Once the WTRU100 reads the L1 cell ID and determines that it is part of the CSG cell whitelist 230, the WTRU100 may preferably read only the MIB or SIBs to make the cell unique and avoid collisions so that it does not have to read all SIBs of the HNB cell that the WTRU100 decides to reselect. The WTRU100 may read the MIB/SIB in the same measurement gap as the L1 cell ID or in a second measurement gap.

If the above procedure is initiated due to a manual CSG cell search instruction by the user, the WTRU100 preferably notifies the user of any nearby CSG cells 110, for example by application, wherein the CSG cells 110 have acceptable quality and the user has accessed the CSG cells 110. The notification preferably includes an identification of the CSG cell 110 sent to the user.

If the user manually selects the CSG cell 110 to provide to the user, the WTRU100 preferably requests a handover from the network 105 to the appropriate CSG cell 110 on the condition that the WTRU autonomously detects the appropriate CSG cell 110. The request may occur in the form of a notification or an event report. The request may be included in any RRC message.

Alternatively, a new RRC message, called RRC event notification message, is proposed to include the notification. The notification preferably includes an identification of the CSG cell 110 that is manually or autonomously selected. The identity may be at least one of a CSG identifier, a PCID, and an HeNBID configured in the CSG cell whitelist 230. Additionally, the notification may include measurements of the selected cell. The measurement may be an actual measurement or manually set to a predetermined value, such as the highest possible value, to force the network 105 to switch to the WTRU 100.

If the user initiates a manual CSG cell search/selection procedure while the WTRU100 is in active mode and the network 105 rejects configuring the WTRU100 with measurement/cell-search gaps at any point, the WTRU100 may indicate to the user that the search for the CSG cell 110 failed, where the WTRU100 needs the measurement/cell-search gaps to perform the procedure or reject the handover request. The indication may explain to the user the reason, such as that the WTRU100 is currently unable to perform a search or that the network 105 rejects the handover request. If the rejection by the network 105 indicates a cause value, the WTRU100 may provide the cause value to the user. The WTRU100, which may be under the direction of the network 105, may be configured to request the user to restart the search at a later instant. The request may include a time indication for the reboot (e.g., five minutes or at 4:00 PM).

If the WTRU100 initiates an autonomous CSG cell search/selection procedure while the WTRU100 is in active mode and the network 105 rejects configuring the WTRU100 with measurement/cell-search gaps at any point, the WTRU100 may choose not to search/evaluate the conditions for searching for the CSG cell 110 for at least a predetermined period of time, where the WTRU100 needs the measurement/cell-search gaps to perform the procedure or reject the handover request. After the predetermined period of time has elapsed, the WTRU100 may again evaluate the conditions, such as GPS coordinates or surrounding cells/TAIDs, that triggered the autonomous CSG cell search. The length of the predetermined time period may change (e.g., may increase) each time the WTRU autonomously fails a CSG cell search. The length of the predetermined period of time may be configured by the network 105.

If the user initiates a manual CSG cell search/selection procedure while the WTRU100 is in active mode, and the WTRU100 moves to idle mode at any point, the WTRU100 may indicate to the user that the search for the CSG cell 110 failed. The indication may explain to the user the reason for moving to idle mode. The WTRU100, which may be under the direction of the network, may be configured to request the user to restart the search at a later instant. The request may include a time indication for the reboot. Alternatively, the WTRU100 may be configured to automatically start applying idle mode procedures for CSG cell search.

When the WTRU100 is making an emergency call, the above procedure is ignored (i.e., not performed) if the user initiates a manual cell search or if the WTRU100 determines that a condition for autonomous CSG cell search (e.g., GPS coordinates) is met. In this case, the WTRU100 may notify the user that the search failed due to the emergency call.

Idle mode mobility

In idle mode, the WTRU100 may be configured to search for the CSG cell 110 due to receiving a manual search instruction from a user or autonomously detecting a condition that triggers a CSG cell search (e.g., GPS coordinates, surrounding cell/TA IDs, or timer expiration). In idle mode, the WTRU100 is preferably configured to perform at least one of the following:

1) the PCIDs of available cells are detected using its receiver 210, wherein the WTRU100 may search for a specific PCID only at the band/center frequency configured for the CSG cell 110 it has access to.

2) Measurements are made on detected cells (e.g., RSRP measurements), where the WTRU100 may only measure those cells whose PCID and/or frequency information match the PCID and/or frequency information of the CSG cell 110 in its CSG cell whitelist 230.

3) It is evaluated whether the measured value of the cell meets an appropriate cell measurement criterion, such as signal strength or quality, for cell selection or cell reselection to the CSG cell 110.

4) Broadcast information, such as MIB, SIB, of the CSG cell 110 is obtained and it is ensured that the broadcast CSG identifier (e.g., CSG TA ID) matches one of the CSG cell whitelists 230 that the WTRU100 has access to. The WTRU100 may perform this step only for those cells whose PCID and/or frequency information match the PCID and/or frequency information of the CSG cell 110 in its CSG cell whitelist 230, and/or those cells whose measurements satisfy the appropriate cell measurement criteria (i.e., signal strength/quality) for cell selection or cell reselection to the CSG cell 110. When the WTRU100 stays in the current cell before reselecting to the cell, the WTRU100 is preferably allowed to read the broadcast information of the neighboring cell. In this manner, the WTRU100 does not have to reselect to a given cell to read its SIBs and determine the cell white list. Alternatively, a new ID smaller than TA may be defined and may be signaled on the MIB or SIB 1. The new ID may be obtained from the TA or cell ID. Once WTRU100 reads the L1 cell ID and determines if it is part of CSG cell whitelist 230, WTRU100 may read only MIB or SIB1 to make the cell unique and avoid collisions, thereby not needing to read all SIBs of HNB cells that WTRU100 decides to reselect.

The above procedure may be modified in idle mode if the WTRU100 is unable to find a suitable CSG cell 110 or macro cell 115 and looks for an acceptable cell for emergency access. Alternatively, the following process may be performed:

1) in addition to specific PCID/band/frequency information, the WTRU100 may search for more information.

2) Alternatively, the WTRU100 may make measurements for all detected cells, not just those CSG cells whose PCID and/or frequency information match the PCID and/or frequency information of the CSG cell 110 in its CSG cell white list 230.

3) Alternatively, the WTRU100 may acquire broadcast information for all detected CSG cells 110, not just those CSG cells whose PCID and/or frequency information match the PCID and/or frequency information of the CSG cell 110 in its CSG cell white list 230, provided that the measurements of these cells satisfy acceptable cell measurement criteria for cell selection or reselection to the CSG cell 110.

Mobility detection, including cell count or any other defined method, may not work best when the WTRU100 reselects to an HNB cell, given the size of the HNB cell. Thus, when the WTRU100 reselects to an HNB cell, additional factors for speed-based detection may be signaled. This parameter is preferably referred to as the speed parameter of the HNB. For example, if the method used is cell counting, the speed parameter of the HNB may add a scaling factor to the number of cells that need to be counted to determine a high or medium mobility situation.

Alternatively, a network-based speed detection scheme may be used when the WTRU100 is handed off to the HNB.

Alternatively, if the WTRU100 detects that it is in a mobility situation, the WTRU100 may be configured to perform a Random Access Channel (RACH) procedure by moving to a connected state and performing a handover, where the network 110 may take care of the subsequent procedures.

Exporting CSG to macrocell mobility

If the WTRU100 is currently occupying the CSG cell 110, the WTRU100 may store macro cell parameters 235 associated with at least one macro cell 115 that the WTRU100 was recently occupied or was connected to before being reselected or handed over to the current CSG cell. The initial reselection or handover from the macro cell 115 to the CSG cell 110 may have been triggered by any reason, such as a manual request or a WTRU autonomous search. The last macrocell 115 parameter that the WTRU100 chooses to remember may include at least one of: frequency band, center frequency, physical cell ID (pci), cell common ID (cgi), and TA ID. While in idle mode, if the WTRU100 detects that it is leaving the coverage area or has no longer been covered by the current CSG cell, the WTRU100 may preferentially reselect to the macro cell 115 that was stored as the last cell. Thus, the WTRU100 may be configured to select to perform at least one of the following: the method comprises the steps of measuring a previous macro cell, measuring the center frequency of the previous macro cell, measuring the frequency layer of the previous macro cell, and preferentially reselecting the previous macro cell.

Detection and measurement of CSG cells

A procedure for CSG cell detection and measurement is now described, assuming that the WTRU100 is camped on a macro cell 115 and there are surrounding CSG cells provided for extension of coverage. In this case, when the serving cell reaches below a certain threshold, the WTRU100 sends a report to the serving cell informing the serving cell that it has reached below an absolute threshold (configured by the network 105). The threshold for starting the CSG cell search and identification procedure may be different from the threshold for the conventional intra-frequency/inter-RAT measurement.

Presence of intra-frequency neighbors

The WTRU100 may measure surrounding neighbor cells at the same frequency in parallel and upon finding that a certain set of neighbor cells is above a threshold (configured by the network 105), the WTRU100 may report the neighbor cell PCIs to the network 105, arranging the neighbor cells in order of serving signal strength in the measurement report. For a cell with a PCI belonging to a PCI that uses the reserved PCI space for a CSG cell, its threshold may be different from that of a cell that does not use such a PCI.

If the WTRU100 detects a cell, the WTRU100 may read the MIB and SIB to ensure that the upper layer identity (e.g., GCI or CGI, including Public Land Mobile Network (PLMN) identity plus cell identity and/or eNB/HeNB identity) of the CSG cell 110 is present in the CSG cell whitelist 230 if at least one of the following conditions is met:

1) the detected PCI of the cell belongs to the PCI space reserved for the CSG cell 110;

2) the PCI of the detected cell is configured in the WTRU 100;

3) the detected cell is above a certain threshold; or

4) The WTRU100 has at least one of the CSG cell whitelists 230 identified on its upper layer.

To read the upper layer identity of the neighbor cell, the WTRU100 may first determine whether it has a DRX gap sufficient to read the MIB and SIBs of the neighbor cell. If the DRX gap is long enough, the WTRU100 may read the MIB and SIB using the DRX gap.

If the length of the DRX gap is not sufficient to read the neighbor cell's MIB and SIB, the WTRU100 may request a measurement gap from the network 105, or the WTRU100 may autonomously adjust away to read the neighbor cell's MIB and SIB.

To request measurement gaps from the network, the WTRU100 may have one bit/flag in it when sending a measurement report indicating that the sent measurement report is for requesting upper layer identity to read a neighboring cell. Alternatively, or in addition to the above-described measurements of the surrounding neighbor cells, when the WTRU100 sends a report to the network 105 indicating the neighbor cells, the WTRU100 may set a flag/bit indicating to the network 105 that it needs gaps to measure the MIB, SIBs, and, if needed, other SIBs of the neighboring CSG cell 110.

Alternatively, the WTRU100 may always autonomously adjust away or request measurement gaps from the network 105 to read the neighbor cell's MIB and SIBs without concern for whether it has a DRX cycle.

In order to decide when to adjust away and create WTRU100 own gaps, WTRU100 may be provided with thresholds for the serving cell and/or neighboring cells. The WTRU100 may then adjust away when the serving cell is below a threshold and/or the neighboring cell is above a certain threshold. The threshold may be configured by the network 105 through RRC signaling (through dedicated messages or in system information) or through MAC or L1 signaling. In addition, even if the neighbor cell is above a certain threshold or the serving cell is below a certain threshold, the WTRU100 may be specified as: only if the PCI of a CSG cell is part of its PCI list, the WTRU100 may only adjust away to read the neighboring CSG cell upper layer identity.

Alternatively, the WTRU100 may simply adjust away and create its own gap, provided that the WTRU100 receives a signal from the network 105 that allows it to do so. The signal may be sent to the WTRU100 as an L1, MAC, or RRC signal. Alternatively, or in addition, the WTRU100 may not read the CSG cell MIB or SIB at all, even if it has a long enough DRX cycle, unless the network 105 sends an L1, MAC, or RRC signal to the WTRU100 that allows it to do so. In such a case, the network 105 may decide to: since there may be macro cells 115 to which the WTRU100 may still be handed over, the WTRU100 does not need to read the upper layer identity of the neighboring CSG cell.

To prevent a complete loss of synchronization with the network 105, the WTRU100 may send a MAC signal to the network 105 that informs the network 105 that the WTRU100 is adjusting away. The WTRU100 may generate L1 signaling instead of MAC signaling. Alternatively, or in addition, the WTRU100 may generate some sort of RRC signaling (e.g., measurement report) and optionally inform the network 105 in the form of an indication: the WTRU100 is adjusting away to read neighbor cell broadcast information.

When the WTRU100 adjusts away, it may adjust away for a longer time until it finishes reading the MIB and SIBs of the neighbor cell (and other system information messages if needed), or it may adjust away at a shorter predetermined time interval with short gaps between them and continue. The length of the time interval during which the WTRU100 adjusts away and the gaps between time intervals may be configured by the network 105 through dedicated RRC signaling or through broadcast messages or may be defined in the specification. Alternatively, the WTRU100 may make the decision autonomously. Alternatively, or in addition, the WTRU100 may report the length of time and/or the gap between time intervals that it plans to adjust away in the MAC/L1/RRC signal it sends to the network 105. The length of the time interval may be in units of time slots or frames, for example. For example, the WTRU100 may report/specify the System Frame Number (SFN) and subframe number that it will adjust away in the MAC Control Element (CE) or in the RRC message. The WTRU100 may also specify the time (e.g., SFN and subframe number) it will adjust back (tune back).

Once the WTRU100 finishes reading the upper layer identity of the neighboring CSG cell and (optionally) if the WTRU100 finds that the CSG cell 110 is present in its CSG cell white list 230, the WTRU100 reports the cell to the network 105 through a measurement report or through any other signaling. The WTRU100 may report at least one of a physical cell identity or an upper layer identity of the CSG cell 110. Alternatively, or in addition, the WTRU100 may also report a bit/flag (flag) in its measurement report, which may indicate to the network: the measurement report that is sent has some additional information or the WTRU100 is requesting a handover command through the measurement report. Alternatively, this could also be associated with or implied in the measurement identity (MeasId) contained in the report, rather than using an additional marker.

Once the WTRU100 receives a handover command from the network 105, the WTRU100 may move to a particular CSG cell 110 or any other cell to which the network 105 commands it to move.

Absence of intra-frequency neighbors

If there are no available cells in the current frequency, the WTRU100 may send a measurement report to the network 105 indicating that there are no neighboring cells above a certain threshold. As a possible addition, the WTRU100 may set a bit in the measurement report that is used to request a gap from the network 105 to measure inter-frequency cells. While this gap exists, if the WTRU100 believes that there are CSG cells 110 around, it is also likely that the WTRU100 will set a flag/bit for requesting a gap that is also long enough to read the MIB/SIB of the CSG cell 110.

Alternatively, the WTRU100 may also autonomously create gaps or use its DRX to perform inter-frequency cell measurements or may create gaps only when the DRX cycle is not complete enough or when there is no DRX cycle at all.

The WTRU100 measures inter-frequency neighbor cells and sends reports to the network 105 that rank the neighbor cells in order of signal strength priority. Alternatively, if the WTRU reads the upper layer identity of the neighboring CSG cell while measuring the neighboring inter-frequency cell, the WTRU100 may only send a measurement report including a handover command request.

Once the WTRU100 receives a handover command from the network 105, the WTRU100 moves to a specific CSG cell 110 or any other cell that the network 105 commands it to camp on.

In the above description, where both inter-frequency and intra-frequency neighbors are involved, the network 105 may configure the WTRU100 to autonomously adjust away or request measurement gaps or use its DRX gaps to perform neighbor cell measurements in the inter-frequency case, or read neighbor cell upper layer identities in the intra-frequency or inter-frequency case.

Minimizing service degradation and/or packet loss

When the WTRU100 autonomously adjusts away from its serving eNB or cell (e.g., to perform measurements or verify PCI or GCI), service degradation and/or packet loss may occur because the serving eNB may schedule traffic to the WTRU100 that has not yet received. If the time it takes for the WTRU100 to perform a spontaneous adjustment away or gap creation is not long enough, it may also result in triggering a reset or re-establishment criteria (e.g., via Radio Link Control (RLC)), which may result in further packet loss.

To minimize service degradation, the WTRU100 may decide to autonomously adjust away, the WTRU100 signals the serving eNB to instruct the serving eNB to: the WTRU100 will or may autonomously adjust away. The signal may be an RRC message or Information Element (IE), or a MAC CE. Alternatively, the signal may be a flag/bit in a measurement report sent from the WTRU100 to the serving eNB. For example, when the WTRU100 sends a measurement report to the network 105 indicating a neighboring cell, the WTRU100 will set a flag/bit that indicates to the network 105 that the WTRU100 is planning to adjust away (e.g., to measure the MIB, SIBs, and other SIBs of neighboring HNB cells, if needed). Once the eNB receives the signal, the eNB may discontinue scheduling downlink traffic (and possibly uplink traffic if needed) to the WTRU 100. Alternatively, the eNB may expedite scheduling of downlink traffic before the WTRU100 adjusts away (i.e., in response to the signal, the eNB will affect its traffic scheduling for such WTRU100 in the way it considers most appropriate). The signal optionally comprises any one or more of:

1) reason for traffic termination request, or reason for adjustment departure;

2) the time of departure (e.g., SFN and/or subframe number) will be adjusted by the WTRU 100; and/or

3) The time (e.g., SFN and/or subframe number) that the WTRU100 will adjust back.

Alternatively, the maximum WTRU-adjusted departure time may be (pre-) defined as a parameter in an RRC message or IE (e.g., the maximum autonomous-adjusted departure time parameter that the WTRU100 will send/notify the network 105 of the WTRU100, or the network 105 will notify the WTRU100 of the maximum autonomous-adjusted departure time parameter).

The WTRU100 may optionally wait for an acknowledgement from the serving eNB before actually adjusting away. The response may be one or more of the following:

1) a response signal (e.g., RRC message or IE, or MAC CE) sent by the serving eNB in response to the signal sent from the WTRU 100;

2) a hybrid automatic repeat request (HARQ) acknowledgement on a HARQ Protocol Data Unit (PDU) carrying a signal of the WTRU;

3) RLC-level acknowledgement (i.e., RLC status report) for acknowledging the RLC PDU carrying the WTRU's signal (in case of an RRC message/WTRU being used as the signal). If the WTRU100 receives such an acknowledgement, then the WTRU100 will make an adjustment away from the serving eNB.

Alternatively, if the WTRU100 adjusts back (e.g., after completing its measurements or after verifying PCI or GCI), the WTRU100 may send another signal to the serving eNB. Such a signal may be an RRC message or IE, or a MAC CE. Such a signal indicates to the serving eNB: the WTRU100 has adjusted back and is thus ready to receive traffic.

Measurement report structure of WTRU

According to the 3GPP specifications, if the measurement report sent by the WTRU100 includes multiple cells and the measurement quantity is not provided for each cell, the WTRU measurement reports will include the cells in order of decreasing quantity (i.e., the best cell is included first).

For the HeNB cell, it may be performed in the same steps as currently specified in 3GPP, or it may be identified by a specific order or location within the measurement report. As an example, the first cell reported in the measurement report may be the HeNB cell of the WTRU (regardless of the value of the measurement quantity, as long as such quantity is acceptable above a suitable threshold). The step where the HeNB cell can be identified by a specific order is more favored than the 3GPP specified step, since it allows the WTRU's preferred order for its HeNB cell to be indicated in the measurement report.

Typically, some (or all) types of measurement reports for a WTRU will be ordered according to the order of preference of the WTRU (e.g., handover preference order). For example, the WTRU measurement reports would include the cells in descending order of preference (i.e., first include the most preferred cell). In the case where the WTRU100 prefers to handover to the HeNB cell, this will be reflected in the measurement report and thus the serving eNB will attempt to prioritize the handover according to the WTRU preference order.

Fig. 3 is a flow diagram of a process 300 for searching for CSG cells. Referring to fig. 1-3, a transmitter 220 in the WTRU100 is configured to transmit a measurement/cell-search gap request message to the network 105 of the CSG cell 110 via an antenna 205. The request message includes a cause value having at least one bit that indicates whether transmission of the request message is due to a manual cell search instruction or a WTRU autonomous determination (step 305). In step 310, the network 105 sends a measurement/cell-search assignment message to the receiver 210 of the WTRU100, the receiver 210 configured to receive the assignment message via the antenna 205. The WTRU100 may transmit a second measurement/cell-search gap request message, if needed (step 315).

Fig. 4 is a flow diagram of a process 400 for searching CSG cells. Referring to fig. 1, 2 and 4, the processor 215 in the WTRU100 is configured to determine whether it has a DRX gap long enough to read the MIB and SIBs of the neighboring CSG cell 110 (step 405). The transmitter 220 in the WTRU100 is configured to transmit a measurement/cell-search gap request message if the DRX gap is not long enough (step 410).

Fig. 5 is a flow diagram of a process 500 for searching for CSG cells. Referring to fig. 1, 2 and 5, the processor 215 in the WTRU100 is configured to determine whether it has a DRX gap long enough to read the MIB and SIBs of the neighboring CSG cell 110 (step 505). The receiver 210 and transmitter 220 in the WTRU100 are configured to autonomously adjust away from the cell currently serving the WTRU100 to read the MIB and SIBs if the DRX gap is not long enough (step 510).

Examples

1. A method performed by a wireless transmit/receive unit (WTRU) for searching for Closed Subscriber Group (CSG) cells, the method comprising:

the WTRU transmitting a measurement/cell-search gap request message including a cause value having at least one bit indicating whether transmission of the measurement/cell-search gap request message is due to a manual cell search instruction or a WTRU unsolicited determination; and

the WTRU receives a measurement/cell-search gap allocation message in response to the measurement/cell-search gap request message.

2. The method of embodiment 1, further comprising:

the WTRU transmits a second measurement/cell-search gap request message on a condition that the WTRU requires a gap to acquire broadcast information associated with a particular CSG cell.

3. The method of embodiment 1, further comprising:

the WTRU transmits a second measurement/cell-search gap request message on a condition that the measurements performed on the detected cell match frequency information of CSG cells on a CSG cell whitelist accessed by the WTRU.

4. The method of embodiment 1, further comprising:

the WTRU transmits a second measurement/cell-search gap request message on a condition that the measurements performed on the detected cell match physical layer cell identifiers (PCIDs) of CSG cells on a CSG cell whitelist accessed by the WTRU.

5. The method according to any of embodiments 1-4, wherein the measurement/cell-search gap request message is a dedicated Radio Resource Control (RRC) message.

6. The method according to any of embodiments 1-4, wherein the measurement/cell-search gap request message is a Radio Resource Control (RRC) event notification message.

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

the WTRU transmits a message requesting handover to an appropriate CSG cell manually selected by a user of the WTRU.

8. A method performed by a wireless transmit/receive unit (WTRU) for searching for Closed Subscriber Group (CSG) cells, the method comprising:

the WTRU determining whether the WTRU has a Discontinuous Reception (DRX) gap of sufficient length to read a Master Information Block (MIB) and a System Information Block (SIB) of a neighboring CSG cell; and

on a condition that the DRX gap is not long enough, the WTRU transmits a measurement/cell-search gap request message.

9. A method performed by a wireless transmit/receive unit (WTRU) for searching for Closed Subscriber Group (CSG) cells, the method comprising:

on a condition that the DRX gap is not long enough, the WTRU autonomously adjusts away from a cell currently serving the WTRU to read the MIB and SIBs of the neighboring CSG cell.

10. A wireless transmit/receive unit (WTRU) for searching for neighboring Closed Subscriber Group (CSG) cells, the WTRU comprising:

a transmitter configured to transmit a measurement/cell-search gap request message including a cause value having at least one bit indicating whether transmission of the measurement/cell-search gap request message is due to a manual cell search instruction or a WTRU autonomous determination; and

a receiver configured to receive a measurement/cell-search gap allocation message in response to the measurement/cell-search gap request message.

11. The WTRU of embodiment 10 wherein the transmitter is further configured to transmit a second measurement/cell-search gap request message on a condition that the WTRU requires a gap to acquire broadcast information associated with a particular CSG cell.

12. The WTRU of embodiment 10 wherein the transmitter is further configured to transmit a second measurement/cell-search gap request message on a condition that measurements performed on the detected cell match frequency information of CSG cells on a CSG cell whitelist accessed by the WTRU.

13. The WTRU of embodiment 10 wherein the transmitter is further configured to transmit a second measurement/cell-search gap request message on a condition that a measurement performed on a detected cell matches a physical layer cell identifier (PCID) of a CSG cell on a CSG cell whitelist accessed by the WTRU.

14. The WTRU as in any one of embodiments 10-13 wherein the measurement/cell-search gap request message is a dedicated Radio Resource Control (RRC) message.

15. The WTRU as in any one of embodiments 10-13 wherein the measurement/cell-search gap request message is a Radio Resource Control (RRC) event notification message.

16. The WTRU as in any one of embodiments 10-15 wherein the WTRU is further configured to transmit a message requesting handover to an appropriate CSG cell manually selected by a user of the WTRU.

17. A wireless transmit/receive unit (WTRU) for searching for Closed Subscriber Group (CSG) cells, the WTRU comprising:

a processor configured to determine whether the processor has a Discontinuous Reception (DRX) gap of sufficient length to read a Master Information Block (MIB) and a System Information Block (SIB) of a neighboring CSG cell; and

a transmitter configured to transmit a measurement/cell-search gap request message on a condition that the DRX gap is not long enough.

18. A wireless transmit/receive unit (WTRU) for searching for Closed Subscriber Group (CSG) cells, the WTRU comprising:

a processor configured to determine whether the processor has a Discontinuous Reception (DRX) gap of sufficient length to read a Master Information Block (MIB) and a System Information Block (SIB) of a neighboring CSG cell;

a receiver; and

a transmitter and a receiver, wherein the receiver and transmitter are configured to autonomously adjust away from a cell currently serving the WTRU to read the MIB and SIBs of the neighboring CSG cell on a condition that the DRX gap is not long enough.

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 executed 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.

A processor associated with software may be used to implement a radio frequency transceiver for controlling a Wireless Transmit Receive Unit (WTRU), User Equipment (UE), terminal, base station, radio networkA 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

2. The method of claim 1, further comprising:

3. The method of claim 1, further comprising:

4. The method of claim 1, further comprising:

5. The method of claim 1, wherein the measurement/cell-search gap request message is a dedicated Radio Resource Control (RRC) message.

6. The method of claim 1, wherein the measurement/cell-search gap request message is a Radio Resource Control (RRC) event notification message.

7. The method of claim 1, further comprising:

11. The WTRU of claim 10, wherein the transmitter is further configured to transmit a second measurement/cell-search gap request message on a condition that the WTRU requires a gap to acquire broadcast information associated with a particular CSG cell.

12. The WTRU of claim 10 wherein the transmitter is further configured to transmit a second measurement/cell-search gap request message on a condition that measurements performed on the detected cell match frequency information of CSG cells on a CSG cell whitelist accessed by the WTRU.

13. The WTRU of claim 10 wherein the transmitter is further configured to transmit a second measurement/cell-search gap request message on a condition that a measurement performed on a detected cell matches a physical layer cell identifier (PCID) of a CSG cell on a CSG cell whitelist accessed by the WTRU.

14. The WTRU of claim 10 wherein the measurement/cell-search gap request message is a dedicated Radio Resource Control (RRC) message.

15. The WTRU of claim 10 wherein the measurement/cell-search gap request message is a Radio Resource Control (RRC) event notification message.

16. The WTRU of claim 10 wherein the transmitter is further configured to transmit a message requesting handover to an appropriate CSG cell manually selected by a user of the WTRU.

a receiver; and