WO2015036017A1

WO2015036017A1 - Enhanced mobility based on random access-free handover in wireless network

Info

Publication number: WO2015036017A1
Application number: PCT/EP2013/068803
Authority: WO
Inventors: Bernhard Wegmann; Richard Waldhauser
Original assignee: Nokia Solutions And Networks Oy
Priority date: 2013-09-11
Filing date: 2013-09-11
Publication date: 2015-03-19

Abstract

A technique is provided for performing, by a mobile station (MS), a random access-free and intra-base station (BS) handover from a serving cell to a target cell by the MS using a time offset value (e.g., timing advance) for synchronization with the target cell that was used by the MS for the serving cell, both the serving cell and the target cell being provided by the same BS and antenna system. Also, a synchronized group handover may be performed for a group of MSs using a random access-free and intra-BS handover in which a same switch time indicator is provided in a handover command to each of the MSs of the group to synchronize the handover for the group to the target cell. These techniques may be used, for example, to provide fast handover after cell deployment changes, such as vertical sectorization where a new cell has been added.

Description

DESCRIPTION

TITLE

ENHANCED MOBILITY BASED ON RANDOM ACCESS-FREE HANDOVER IN

WIRELESS NETWORK

TECHNICAL FIELD

[0001] This description relates to wireless networks.

BACKGROUND

[0002] A communication system may be a facility that enables communication between two or more nodes or devices, such as fixed or mobile communication devices. Signals can be carried on wired or wireless carriers.

[0003] An example of a cellular communication system is an architecture that is being standardized by the 3^rd Generation Partnership Project (3GPP). A recent development in this field is often referred to as the long-term evolution (LTE) of the Universal Mobile Telecommunications System (UMTS) radio-access technology. E-UTRA (evolved UMTS Terrestrial Radio Access) is the air interface of 3GPP's Long Term Evolution (LTE) upgrade path for mobile networks. In LTE, base stations, which are referred to as enhanced Node Bs (eNBs), provide wireless access within a coverage area or cell. In LTE, mobile devices, or mobile stations are referred to as user equipments (UE). LTE has included a number of improvements or developments.

[0004] In LTE, a UE (or mobile station) may perform handover from a current (or source) cell to a target cell by measuring and reporting signal quality for one or more neighbor cells to a current eNB or current cell. If the channel quality for a neighbor cell is better than the current cell, then the UE may receive a handover command in the form of a RRCConnectionReconfiguration message including the physical cell ID (PCI) of the target cell, a C-RNTI (temporary identifier for the UE within the target cell), and possibly a random access preamble. The UE may then use a random access procedure to obtain a timing advance from the target cell to allow the UE to transmit data in the uplink (UL) direction. For a contentionless random access, the UE may send a random access request including the random access preamble to the target cell, and the target cell may return a random access response including an uplink grant and a time offset value (e.g., timing advance). The UE may then indicate that the handover to the target cell is completed by sending a Handover confirm message, e.g., a

RRCConnectionReconfigurationComplete message, to the target cell. SUMMARY

[0005] According to an example implementation, a method may

includeperforming, by a mobile station (MS), a random access-free and intra-base station (BS) handover from a serving cell to a target cell by the MS using a time offset value for synchronization with the target cell that was used by the MS for the serving cell, both the serving cell and the target cell being provided by a same BS and antenna system.

[0006] According to another example implementation, an apparatus may include at least one processor and at least one memory including computer instructions, when executed by the at least one processor, cause the apparatus to perform, by a mobile station (MS), a random access-free and intra-base station (BS) handover from a serving cell to a target cell by the MS using a time offset value for synchronization with the target cell that was used by the MS for the serving cell, both the serving cell and the target cell being provided by a same BS and antenna system, the apparatus being caused to perform includes the apparatus being caused to: determine, by the MS, a time offset value used by the MS for the serving cell; receive, by the MS, a handover command from the BS instructing the MS to perform a handover from the serving cell to the target cell, the handover command including at least a cell ID for the target cell, an identifier for the MS for the target cell, and a switch time indicator that indicates when the MS should switch to the target cell; and, send, based on the handover information received by the MS and the time offset value, a handover confirm message from the MS to the BS to confirm that the handover of the MS to the target cell has been completed.

[0007] In another example implementation, a computer program product is provided, the computer program product including a non-transitory computer-readable storage medium and storing executable code that, when executed by at least one data processing apparatus, is configured to cause the at least one data processing apparatus to perform a method including performing, by a mobile station (MS), a random access-free and intra-base station (BS) handover from a serving cell to a target cell by the MS using a time offset value for synchronization with the target cell that was used by the MS for the serving cell, both the serving cell and the target cell being provided by a same BS and antenna system.

[0008] According to another example implementation, a method is provided for facilitating a random access-free and intra-base station handover from a serving cell to a target cell, both the serving cell and the target cell being provided by a same base station (BS) and antenna system. The method includes: transmitting, from the BS to a mobile station (MS), a handover command instructing the MS to perform a handover from the serving cell to the target cell, the handover command including at least a cell ID for the target cell, an identifier for the MS for the target cell, a time offset value for synchronizing the MS with the target cell, and a switch time indicator that indicates when the MS should switch to the target cell, the time offset value for the new cell for the MS being the same as a time offset value for the serving cell; and receiving, by the BS, a handover confirm message from the MS that confirms that the handover of the MS to the target cell has been completed.

[0009] According to yet another example implementation, an apparatus includes at least one processor and at least one memory including computer instructions, when executed by the at least one processor, cause the apparatus to: transmit, from the BS to a mobile station (MS), a handover command instructing the MS to perform a handover from the serving cell to the target cell, the handover command including at least a cell ID for the target cell, an identifier for the MS for the target cell, a time offset value for synchronizing the MS with the target cell, and a switch time indicator that indicates when the MS should switch to the target cell, the time offset value for the new cell for the MS being the same as a time offset value for the serving cell; and receive, by the BS, a handover confirm message from the MS that confirms that the handover of the MS to the target cell has been completed.

[0010] According to yet another example implementation, a computer program product includes a non-transitory computer-readable storage medium and storing executable code that, when executed by at least one data processing apparatus, is configured to cause the at least one data processing apparatus to perform a method including: transmitting, from the BS to a mobile station (MS), a handover command instructing the MS to perform a handover from the serving cell to the target cell, the handover command including at least a cell ID for the target cell, an identifier for the MS for the target cell, a time offset value for synchronizing the MS with the target cell, and a switch time indicator that indicates when the MS should switch to the target cell, the time offset value for the new cell for the MS being the same as a time offset value for the serving cell; and receiving, by the BS, a handover confirm message from the MS that confirms that the handover of the MS to the target cell has been completed.

[0011] According to yet another example implementation, a method of

synchronizing a handover for a group of mobile stations to a target cell is provided that includes: receiving, by a base station (BS), a measurement report from each of a plurality of mobile stations (MSs) of a group of MSs for at least the target cell, each of the measurement reports indicating the target cell for handover; and transmitting, from the BS to each of the MSs of the group, a respective handover command instructing the MS to perform a handover to the target cell, each respective handover command including at least a cell ID for the target cell, an identifier for the MS for the target cell, a time offset value for synchronizing the MS with the target cell, and a switch time indicator that indicates when the MS should switch to the target cell, the time offset value for the new cell for the MS being the same as a time offset value for the serving cell for the MS, wherein the switch time indicator provided to each of the MSs of the group indicating a same time so as to synchronize the handovers of the MSs of the group.

[0012] According to yet another example implementation, an apparatus includes at least one processor and at least one memory including computer instructions, when executed by the at least one processor, cause the apparatus to: receive, by a base station (BS), a measurement report from each of a plurality of mobile stations (MSs) of a group of MSs for at least the target cell, each of the measurement reports indicating the target cell for handover; and transmit, from the BS to each of the MSs of the group, a respective handover command instructing the MS to perform a handover to the target cell, each respective handover command including at least a cell ID for the target cell, an identifier for the MS for the target cell, a time offset value for synchronizing the MS with the target cell, and a switch time indicator that indicates when the MS should switch to the target cell, the time offset value for the new cell for the MS being the same as a time offset value for the serving cell for the MS, wherein the switch time indicator provided to each of the MSs of the group indicating a same time so as to synchronize the handovers of the MSs of the group.

[0013] According to yet another example implementation, a computer program product includes a non-transitory computer-readable storage medium and stores executable code that, when executed by at least one data processing apparatus, is configured to cause the at least one data processing apparatus to perform a method including: receiving, by a base station (BS), a measurement report from each of a plurality of mobile stations (MSs) of a group of MSs for at least the target cell, each of the measurement reports indicating the target cell for handover; and transmitting, from the BS to each of the MSs of the group, a respective handover command instructing the MS to perform a handover to the target cell, each respective handover command including at least a cell ID for the target cell, an identifier for the MS for the target cell, a time offset value for synchronizing the MS with the target cell, and a switch time indicator that indicates when the MS should switch to the target cell, the time offset value for the new cell for the MS being the same as a time offset value for the serving cell for the MS, wherein the switch time indicator provided to each of the MSs of the group indicating a same time so as to synchronize the handovers of the MSs of the group.

[0014] The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features will be apparent from the description and drawings, and from the claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] FIG. 1 is a block diagram of a wireless network 130 according to an example implementation.

[0016] FIG. 2 is a diagram illustrating cell deployment changes according to an example implementation.

[0017] FIG. 3 is a diagram illustrating a random access-free and intra-BS handover according to an example implementation.

[0018] FIG. 4 is a flow chart illustrating operation of a mobile station according to an example implementation.

[0019] FIG. 5 is a flow chart illustrating operation of a base station (BS) according to an example implementation.

[0020] FIG. 6 is a flow chart illustrating operation of a base station (BS) according to an example implementation.

[0021] FIG. 7 is a block diagram of a wireless station (e.g., BS or MS) 700 according to an example implementation. DETAILED DESCRIPTION

[0022] According to an example implementation, techniques are provided to allow a random access free (or RACH-free) and intra-BS handover for a group of MSs in a synchronized manner to a new or target cell. This synchronized group handover may be performed quickly after cell deployment changes, such as vertical sectorization, because a random access procedure is not performed. Rather, because the radio link properties are the same for each MS for both an original cell and the new cell (since both original cell and new cell are provided by the same BS and antenna system), the time offset value (or timing advance) is known by the MS and the BS prior to new/target cell activation.

Alternatively, the time offset value for a MS may be provided in the handover command from the BS without using a random access procedure. In addition, a same switch time indicator may be provided in the handover commands to each MS of the group, where the switch time indicator identifies a time when each MS should switch to the new cell.

Therefore, the use of a same switch time indicator for the group may allow the handover of the group of MSs to the new cell to be synchronized or performed at the same time. A similar technique may be used to provide an intra-BS and random access-free handover for a single MS based on mobility.

[0023] FIG. 1 is a block diagram of a wireless network 130 according to an example implementation. In the wireless network 130 of FIG. 1 , mobile stations (MSs) 132 and 133, which may also be referred to as user equipments (UEs), may be connected (and in communication) with a base station (BS) 134, which may also be referred to as an enhanced Node B (eNB). BS 134 provides wireless coverage within a cell 136. This is merely one simple example of a wireless network, and others may be used. For example, only two MSs are shown, but any number may be used.

[0024] FIG. 2 is a diagram illustrating cell deployment changes according to an example implementation. A base station 210 is connected to an antenna system 212 which provides an original cell 214. Antenna system 212 may be, for example, an active antenna system that may be used to perform, for example, vertical beam forming (or vertical sectorization) or cell splitting in which signal processing techniques may be used to perform directional signal transmission in order to provide multiple cells from the same BS and antenna system. For example, in cell splitting, an additional radiation pattern may be generated from the same active antenna system to provide the new cell within the original range of the original cell. In this manner, an active antenna system (AAS) may be used to improve the wireless coverage (e.g., wider coverage areas) and/or capacity (e.g., can handle a larger number of MSs or users) offered by a BS and antenna system.

[0025] As shown in figure 2, one example of cell deployment changes may involve a dynamic cell splitting which may involve vertical sectorization in which an original cell 214 may be split into two smaller cells, such as an inner cell 216 and an outer cell 218. Original cell 214 may have a physical cell ID (PCI) of PCI_5, for example. The cells 216 and 218 also include PCIs such as PCI_8 for inner cell 216 and PCI_5 for outer cell 218.

In this example, one of the smaller cells, outer cell 218 in this case, has inherited the PCI (PCI_5) of the original cell 214. Although in general, the original cell and the subsequent cells after any cell deployment changes may have different PCIs.

[0026] A number of MSs within original cell 214 may be connected to or in communication with BS 210. For example, MSs 220, 222, 224 and 226 may be within cell

214 prior to cell splitting. After cell splitting, some of the MSs will be moved or changed to a different cell, e.g., via MS handover. The handover or cell change may be performed, for example, based on MS measurement of signals (e.g., signal strength, signal quality or other signal measurement) by the MS from each cell. As shown in FIG. 2, MSs 220 and 222 may remain in the outer cell 218 (PCI_5), e.g., if the measurement from such MSs indicates that outer cell 218 is the best cell. In this example, because the PCI (PCI_5) for the outer cell 218 is the same as the PCI (PCI_5) for the original cell 214, no cell change or handover is required for MSs 220 and 222, since these MSs will remain with the cell having PCI of PCI_5. On the other hand, based on signal measurements of signals from cells 216 and 218, MSs 224 and 226 may each indicate that the best cell for them is inner cell 216 (PCI_8). Therefore, because the target cell (inner cell 216) has a PCI (PCI_8) that is different than the PCI (PCI_5) of the currently serving cell (original cell 214), a handover or cell change is required to move or switch MSs 224 and 226 from the original cell 214 (PCI_5) to the inner cell 216 (PCI_8). While only four MSs are shown in this example, any number of MSs may be provided within original (or currently serving) cell 214, and a handover or cell change may be performed for any number of MSs to one of the new cells based on the cell splitting or vertical sectorization.

[0027] Current handover or cell change techniques are designed to accommodate normal user/MS mobility where, typically based on movement of the MS, another cell becomes the best cell and a corresponding handover is triggered by the MS signal measurements. As part of the handover procedure, a MS may typically use a limited or shared resource to obtain timing information (or other information) from the target cell/BS in order to complete the handover. For example, in some cases, after receiving a

Handover command (which may include a random access preamble), a MS may use a random access channel (RACH) to submit a random access request that includes the random access preamble to the target cell/BS. The target cell/BS estimates the transmission timing of the MS based on the random access preamble. The target BS then responds with a random access response that may include a time offset value (e.g., a timing advance) that may be used by the MS to adjust the timing of its transmission so it may transmit, in a synchronized manner, via an uplink channel to the target BS. The time offset value for the MS may be a function of the MS-BS radio link properties, such as the distance from the MS to the BS and antenna system.

[0028] Several problems may arise when attempting to apply current handover procedures to the handover of a group of MSs to a new cell based on cell deployment changes. First, if handovers of various MSs of the group are performed over a period of time or a staggered fashion (e.g., not at the same time), then signals from MSs connected to the original cell 214 may interfere with signals transmitted by MSs connected to one of the new cells (e.g., inner cell 216 or outer cell 218). This signal interference can cause a radio link failure for one or more of these MSs. Therefore, according to an example implementation, to avoid this type of signal interference, the handover (or cell-switch) for the group of MSs to the new cell (e.g., inner cell 216 in this example) may be performed (or completed) in a synchronized manner, or at the same time. [0029] However, current handover procedures are not designed for a

synchronized group handover to a cell. First, only a limited number of random access resources (e.g., limited number of random access channels) are typically available at a time for a target cell/BS. Therefore, in the event that there are more MSs identified for handover than there are random access channels, this may, therefore, result in handover for the group of MSs being performed in a staggered (non-synchronized) fashion, which may result in signal interference and radio link failure, as noted above, since this may cause some of the MSs to perform the handover before other MSs in the group have performed the handover.

[0030] Secondly, as noted above, the time offset value for a MS is based on the radio link properties (such as the delay) between the MS and the target BS, which is based at least in part on the distance that the MS is from the BS/antenna system for the target cell. In the case of a new cell being created based on cell deployment changes (such as cell splitting shown in FIG. 2), both the original serving cell (e.g., original cell 214) and the new target cell for handover (e.g., inner cell 216) are provided by the same BS and antenna system (BS 210 and antenna system 212). In such case, the handover from original cell 214 to inner cell 216 is an intra-BS handover. As a result, the time offset value (at least at the time of handover) for each MS is the same for both the original cell 214 and the target cell (e.g., inner cell 216) because the radio link properties (e.g., including the distance from the antenna system 212 to the MS) is the same for both cells. The current handover techniques require the MS to perform a procedure, such as the random access procedure, in order to obtain a time offset value (or timing advance) for the MS for the target cell. However, according to an example implementation, an intra-BS handover may skip the random access procedure since both the MS and the BS of the target cell already know the time offset value (or timing advance) for the MS, which is the same for both the current serving (or original) cell and the target cell.

[0031] Therefore, according to an example embodiment, a technique is disclosed for a random access-free (or RACH-free) and intra-BS handover from a serving cell (or current/original cell) to a target cell, where the MS uses a time offset value for the target cell that is the same as the time offset value used by the MS for the original or serving cell

(e.g., source cell). The use of the random access-free and intra-BS handover that uses the previously known time offset value (or timing advance) from a currently serving cell or original cell (without the need for random access procedure) may be used for a synchronized group handover based on cell deployment changes (e.g., cell splitting or combining), and for a single MS handover based on mobility or movement to the new or target cell. [0032] In addition, according to an example implementation, a switch time indicator may be provided by a BS to each MS of a group of MSs identified for

synchronized group handover to a target cell. The switch time indicator may identify a time that the MSs should switch to the target cell, e.g., the time when the handover to the new or target cell should be completed. The switch time indicator may be, for example, a transmission time interval (TTI). At the time indicated by the switch time indicator, each MS of the group of MSs for synchronized handover should cease (or already have ceased) transmitting via resources of their previously serving or original cell, and may begin transmitting via resources of the target cell. In this manner, a synchronized (e.g., at the same time) handover may be performed for a group of MSs to the target cell. Also, this synchronized group handover may be performed without using the random access procedure, based on using the previously known time offset value for each MS.

[0033] FIG. 3 is a diagram illustrating a random access-free and intra-BS handover according to an example implementation. A BS 312 may provide an original cell or source cell that is currently serving one or more MSs, such as MS 310. At 314, cell deployment changes are identified or determined, including a cell splitting in this example to create or add a new (or target) cell, in addition to the original cell. A PCI is identified for the new/target cell, e.g., even before the new cell is activated. In addition, the network may provide MSs with neighbor lists that identify PCIs (physical cell IDS) of neighbor BSs. Once the PCI is identified for the new cell, then neighbor lists may be updated to include the PCI of this new cell. Also, each MS in the original cell may receive an updated list of measurement objects, which may be a list of neighbor cells that the MS should measure their reference signals, and then report back the signal measurements.

[0034] At 316, the BS sends to each of the MSs connected to the BS 312 a measurement configuration message, e.g., a RRCConnectionReconfiguration message with a measConfig information element that adds the PCI for the new cell (as a new measurement object) for signal measurement. A cell-individual offset (CIO) for the new cell being part of the measurement configuration may also be reported to the MS, which may be used when triggering a measurement event for the cell. For example, the strength of the reference signals of the new cell may need to be greater than current cell signal strength plus CIO before a handover indication is sent to the current cell. The

measurement configuration message at 316 may operate to cause each MS to add the PCI of the new cell to its list of measured cells.

[0035] At 318 (FIG. 3), the new cell, provided by BS 312, is activated, and the BS 312 begins preventing MS handovers to the new cell from any cell, e.g., in order to prevent inter-cell interference. For example, as shown in FIG. 2, after activation of inner cell 216 (PCI_8), handovers may be allowed from original cell/outer cell (PCI_5) to inner cell (PCI_8) (e.g., as part of the synchronized group handover), but handovers to inner cell/new cell 216 (PCI_8) would not be allowed from other cells until after the

synchronized group handover has been performed. This is because one or more MSs connected (or attached) to inner cell 216 might cause interference with original cell 214 until the synchronized group handover has been accomplished.

[0036] After activation of the new cell, its reference signal(s) can still be measured by MSs due to higher receiver robustness and advanced interference mitigation from broadcast and reference signals. Also, as noted above, at 316, the list of measurement objects is updated for the MS 310 (and all the MSs of the original cell) to include the PCI of the new cell. Therefore, the MS 310 (and other MSs) begins measuring the reference signals of the new cell, along with continuing to possibly measure reference signals of one or more other cells. The MS 310, and each of the MSs in the group, may then detect a measurement event that indicates a handover should be performed to the new cell based on the signal strength of the reference signals of the new cell compared to the current cell.

[0037] At 320, each MS, including MS 310, provides a measurement report to BS 312, indicating the new/target cell for handover (e.g., as the best serving cell for the MS based on measured signals). Thus, each MS of the group of MSs will provide a measurement report to BS 312 indicating handover to the new/target cell.

[0038] At 324, each of the MSs that provided a report indicating handover to the new cell will now be configured for a synchronized and random access-free (without performing random access procedure) handover to the new cell. As noted above, the random access procedure in this case is unnecessary because the time offset value (or timing advance) for each MS is known a-priori or in advance (e.g., prior to new cell activation) by both the MS and the BS since this is an intra-BS handover. Therefore, the time offset value will be the same for both the original cell and the new/target cell for each MS. As a result, there is no need for these MSs to perform the random access procedure with new/target cell/BS.

[0039] To instruct each MS of the group of MSs to perform the synchronized handover to the new cell, at 322, the BS 312 sends a separate handover command to each MS instructing the MS to perform handover to the new/target cell at a specific time. The handover (HO) command may be, for example, a RRCConnectionReconfiguration message including a mobilitycontrollnfo information element (which may include, e.g., a PCI for the target/new cell, and a temporary network identifier (e.g., C-RNTI) for the MS in the new cell), and one or more other fields, such as a uplink (UL) and/or downlink (DL) resource grant for the new cell, a time offset value (e.g., timing advance) for the MS in the new cell, and a switch time indicator (e.g., TTI). In one example implementation, the time offset value may be omitted, since the MS already knows the time offset value for the current/original cell, and this current offset value will be used for the target/new cell.

[0040] According to one example implementation, the presence of the time offset value/timing advance in the handover command may inform the MS 310 that the handover to the new/target cell is to be a random access-free handover (not a standard handover that would involve performing the random access procedure). Alternatively, a separate "RACH-free" field may be set to 1 to indicate random access-free handover for the MS. These are merely examples, and other formats and techniques may be used.

[0041] Alternatively, with reference to 322, rather than providing all of the noted parameters in the handover command, one or more of these fields or parameters listed in the handover command may be provided to each MS in one or more messages that may be provided separately (e.g., after) the handover command. Also, one or more of these parameters (e.g., resource grant, time offset value/timing advance, switch time

indicator/TTI) that are indicated as being separate from the mobilityControllnfo information element may be provided as part of the mobilityControllnfo information element.

[0042] At the time (323) specified by the switch time indicator (e.g. at the beginning of a dedicated TTI), each of the MSs of the group will have ceased or stopped transmitting on resources for its original cell and may begin being served (330) by the new/target cell and/or transmitting via resources of the new/target cell.

[0043] At 326, the MS 310 sends a handover confirm message to the BS 312, which may be, for example, a RRCConnectionReconfigurationComplete message, that confirms to the BS that the MS has completed the handover to the new/target cell.

[0044] Also, at 328, at the time (323) specified by the switch time indicator or TTI, the BS 312 will stop preventing MSs from performing handover to the new/target cell.

Thus, after the group of MSs identified for synchronized group handover to the new/target cell has performed handover, then other MSs may resume performing handover to the new/target cell, e.g., based on their cell measurements.

[0045] Therefore, a synchronized group handover may be performed by a BS providing a handover command (such, as for example, a RRCConnectionReconfiguration message) that includes, for example, the PCI of the target cell, an identifier for the MS, a resource grant, a time offset value (e.g., timing advance) and a switch time indicator (e.g., TTI). The switch time indicator indicates a time when the MS (or group of MSs) should switch to the target cell. In the case of a synchronized group handover, the same switch time indicator is provided to all of the MSs selected for group handover. Using a same switch time indicator for each of the MSs of the group ensures that all MSs of the group will switch to the target cell at the same time, thereby avoiding or at least decreasing inter- cell interference.

[0046] Cell merging (or cell combining) may also occur where, for example, the inner cell 216 (FIG. 1 ) may be released due to low traffic load, e.g., due to having fewer than a threshold number of connected users/MSs. According to an example

implementation, as shown in FIG. 1 , inner cell 216 (e.g., PCI_8) may be merged with outer cell 218 (PCI_5) to form an original cell (PCI_5) again that approximately covers the area that the inner and outer cells previously covered. Similar to the case of cell splitting, the random access-free and intra-BS handover may be applied in the case of cell merging. However, in the case of cell merging, according to an example implementation, intra-BS handovers are not triggered based on signal measurements performed by each MS.

Rather, in the case of cell merging, intra-BS and random access free handovers are triggered by a traffic steering forced cell change in which MSs in one cell are moved or switched via synchronized group handover to the other intra-BS cell without using random access procedure, in the same manner as described above for cell splitting. However, for cell merging, the handover is not triggered by a measurement report indicating handover to new cell (320) shown above for FIG. 3. Rather, a decision is made to perform cell merging, and then the handover command is sent by the BS to each of the MSs in one of the cells to be deactivated, with instructions to perform handover to the other intra-BS cell, without using random access procedure. The same fields may be provided in the handover command, such as target PCI, C-RNTI, resource grant, time offset value (or timing advance), and a switch time indicator (or TTI) that indicates a time that the MSs should switch to the other cell (or begin service by the other cell). The empty cell may then be deactivated using the active antenna system.

[0047] Also, for cell merging, MSs are prevented from performing handover to the cell that is being deactivated between synchronized evacuation of the cell until deactivation of the cell. In other words, according to an example implementation, no further handovers to the cell being deactivated are permitted once a synchronized evacuation (synchronized handover to another intra-BS cell) has been performed. Thus, if an inner cell is being deactivated as part of cell merging, no further handovers to the inner cell are permitted once a synchronized evacuation of that inner cell (e.g., synchronized handover of MSs from inner cell to target cell) has been performed. Also, the

measurement configurations are then updated at each MS by removing the inner cell or cell that has been deactivated as a measured object from MS's neighbor list. The deactivated cell may be removed as a measurement object by sending the MSs a measurement configuration message (see 316, FIG. 3) where the deactivated cell is removed as a measurement object in the neighbor list.

[0048] While the timing diagram in FIG. 3 is described with respect to a

synchronized group handover to the new/target cell, this same technique may be used to allow a single MS to perform a random access-free and intra-BS handover based on mobility. Thus, after the creation/activation of the new cell, and then the synchronized group handover to the new/target cell is completed, a first subsequent MS (based on its movement or signal measurements) may perform a random access-free and intra BS handover based on the signals and timing illustrated in FIG. 3. In such case, the switch time value or TTI sent to the MS identifies the time for the MS to switch to the new/target cell, but this time identified by the TTI is only for one MS, not a group of MSs, according to this example. Thus, for example, after the group of MSs has performed a synchronized group handover to the new/target cell, a second subsequent MS, currently in a cell not provided by the BS, may perform a standard (inter-BS, using random access procedure) handover to the new target cell. Therefore, the new/target cell may receive both standard handovers based on a random access procedure, e.g., from MSs connected to other BSs, and random access free and intra-BS handovers from another cell provided by the same BS.

[0049] Therefore, according to an example implementation, techniques are provided to allow a fast and random access free (or RACH-free) and intra-BS handover for a group of MSs in a synchronized manner to reduce interference. This synchronized group handover may be performed very quickly after cell deployment changes, such as vertical sectorization, have been performed, because random access procedure is not performed (since it is unnecessary). For example, the new cell created by cell deployment changes or vertical sectorization is served by the same BS and antenna system as an original or previous cell for the group of MSs. This means that for each of these MSs of the group, the time offset value or timing advance for each MS is the same for both the original cell and the new/target cell, since the time offset value may be based on the properties (such as distance) of the radio link between BS/antenna system and the MS. Since this is an intra-BS handover, the radio link properties between MS and BS are the same, and thus, the time offset value or timing advance is known in advance by both the

BS and the MS, and/or may be quickly provided by the BS to the MS as part of the handover command, without a random access procedure being performed. This allows for the MS to perform fast synchronization to the new/target cell by skipping the random access procedure.

[0050] FIG. 4 is a flow chart illustrating operation of a mobile station according to an example implementation. The method or technique illustrated in FIG. 4 may include several operations. At operation 410, the mobile station (MS) performs performing a random access-free and intra-base station (BS) handover from a serving cell to a target cell by the MS using a time offset value for synchronization with the target cell that was used by the MS for the serving cell, both the serving cell and the target cell being provided by a same BS and antenna system.

[0051] Operation 410 may include operations 420, 430 and 440, according to an example implementation. Operation 420 may include determining, by the MS, a time offset value used by the MS for the serving cell.

[0052] Operation 430 may include receiving, by the MS, a handover command from the BS instructing the MS to perform a handover from the serving cell to the target cell, the handover command providing handover information including at least a cell ID for the target cell, an identifier for the MS for the target cell, a resource assignment for the target cell, and a switch time indicator that indicates when the MS should switch to the target cell.

[0053] Operation 440 may include sending, based on the handover information received by the MS and the time offset value, a handover confirm message from the MS to the BS to confirm that the handover of the MS to the target cell has been completed.

[0054] A number of different implementations will be described with reference to FIG. 4.

[0055] In the flow chart of FIG. 4, the intra-BS handover may be performed as a synchronized group handover to the target cell that is created based on cell splitting.

[0056] In the flow chart of FIG. 4, the MSs are prevented from performing a handover to the target cell between a time the target cell is activated until the

synchronized group handover to the target cell is completed.

[0057] In the flow chart of FIG. 4, the intra-BS handover is performed as a synchronized group handover to the target cell based deactivating the serving cell as part of cell merging.

[0058] In the flow chart of FIG. 4, the MSs are prevented from performing a handover to the serving cell after the synchronized group handover of all MSs in the serving cell to the target cell is completed.

[0059] In the flow chart of FIG. 4, the method may further include receiving, by the MS from the BS in the handover command, a time offset value for the target cell, the time offset for the target cell for the MS being the same as the time offset value for the serving cell for the MS based at least in part on the same BS and antenna system being used to provide both the serving cell and the target cell. [0060] In the flow chart of FIG. 4, the method may further include receiving, by the MS, a measurement configuration message from the serving cell instructing the MS to measure signal strength and/or quality for each of one or more listed cells, the listed cells including the target cell that was added based on cell deployment changes; measuring, by the MS, a reference signal of at least the target cell; and sending, by the MS, a measurement report for at least the target cell to the BS, the measurement report indicating the target cell for handover.

[0061] In the flow chart of FIG. 4, the receiving the measurement configuration message may include receiving RRCConnectionReconfiguration message including a MeasConfig information element.

[0062] In the flow chart of FIG. 4, the switch time indicator may include a transmission time interval (TTI) for the target cell that indicates a time the handover to the target cell is to be completed.

[0063] In the flow chart of FIG. 4, the the receiving a handover command may include receiving, by the MS, a RRCConnectionReconfiguration message with a

MobilityControllnfo information element that includes at least the cell ID for the target cell, the identifier for the MS for the target cell and the resource assignment for the target cell, the handover command also including the switch time indicator that indicates when the MS should switch to the target cell and a time offset value for the MS for the target cell.

[0064] In the flow chart of FIG. 4, the receiving a handover confirm message may include receiving a RRCConnectionReconfigurationComplete message.

[0065] An apparatus may include at least one processor and at least one memory including computer instructions, when executed by the at least one processor, cause the apparatus to perform, by a mobile station (MS), a random access-free and intra-base station (BS) handover from a serving cell to a target cell by the MS using a time offset value for synchronization with the target cell that was used by the MS for the serving cell, both the serving cell and the target cell being provided by a same BS and antenna system. The apparatus being caused to perform includes the apparatus being caused to: determine, by the MS, a time offset value used by the MS for the serving cell; receive, by the MS, a handover command from the BS instructing the MS to perform a handover from the serving cell to the target cell, the handover command including at least a cell ID for the target cell, an identifier for the MS for the target cell, and a switch time indicator that indicates when the MS should switch to the target cell; and, send, based on the handover information received by the MS and the time offset value, a handover confirm message from the MS to the BS to confirm that the handover of the MS to the target cell has been completed. [0066] The apparatus may be further caused to: receive, by the MS from the BS in the handover command, a time offset value for the target cell, the time offset for the target cell for the MS being the same as a time offset value for the serving cell for the MS based at least in part on the same BS and antenna system being used to provide both the serving cell and the target cell.

[0067] In the apparatus, the switch time indicator may include a transmission time interval (TTI) for the target cell that indicates when the MS should switch to the target cell or a time the handover to the target cell is to be completed, and wherein the time offset value comprises a timing advance for the MS for the target cell.

[0068] A computer program product may include a non-transitory computer- readable storage medium and storing executable code that, when executed by at least one data processing apparatus, is configured to cause the at least one data processing apparatus to perform a method including: performing, by a mobile station (MS), a random access-free and intra-base station (BS) handover from a serving cell to a target cell by the MS using a time offset value for synchronization with the target cell that was used by the MS for the serving cell, both the serving cell and the target cell being provided by a same BS and antenna system.

[0069] In the computer program product, the performing the random access-free and intra-BS handover may include: determining, by the MS, a time offset value used by the MS for the serving cell; receiving, by the MS, a handover command from the BS instructing the MS to perform a handover from the serving cell to the target cell, the handover command providing handover information including at least a cell ID for the target cell, an identifier for the MS for the target cell, a resource assignment for the target cell, and a switch time indicator that indicates when the MS should switch to the target cell; and sending, based on the handover information received by the MS and the time offset value, a handover confirm message from the MS to the BS to confirm that the handover of the MS to the target cell has been completed.

[0070] FIG. 5 is a flow chart illustrating operation of a base station (BS) according to an example implementation. The flow chart of FIG. 5 is directed to a method of facilitating a random access-free and intra-base station handover from a serving cell to a target cell, both the serving cell and the target cell being provided by a same base station (BS) and antenna system. FIG. 5 may include several operations, including:

[0071] Operation 510 may include transmitting, from the BS to a mobile station (MS), a handover command instructing the MS to perform a handover from the serving cell to the target cell, the handover command including at least a cell ID for the target cell, an identifier for the MS for the target cell, a time offset value for synchronizing the MS with the target cell, and a switch time indicator that indicates when the MS should switch to the target cell, the time offset value for the new cell for the MS being the same as a time offset value for the serving cell.

Operation 520 may include receiving, by the BS, a handover confirm message from the MS that confirms that the handover of the MS to the target cell has been completed.

[0072] In the method of FIG. 5, the switch time indicator may include a

transmission time interval (TTI) for the target cell that indicates when the MS should switch to the target cell or a time the handover to the target cell is to be completed, and wherein the time offset value comprises a timing advance for the MS for the target cell.

[0073] In the method of FIG. 5, the transmitting a handover command may include transmitting, by the BS, a RRCConnectionReconfiguration message with a

MobilityControllnfo information element that includes at least the cell ID for the target cell, the identifier for the MS for the target cell and a resource assignment for the target cell, the handover command also including the switch time indicator that indicates when the MS should switch to the target cell and the time offset value for the MS for the target cell.

[0074] An apparatus may include at least one processor and at least one memory including computer instructions, when executed by the at least one processor, cause the apparatus to: transmitting, from the BS to a mobile station (MS), a handover command instructing the MS to perform a handover from the serving cell to the target cell, the handover command including at least a cell ID for the target cell, an identifier for the MS for the target cell, a time offset value for synchronizing the MS with the target cell, and a switch time indicator that indicates when the MS should switch to the target cell, the time offset value for the new cell for the MS being the same as a time offset value for the serving cell; and receiving, by the BS, a handover confirm message from the MS that confirms that the handover of the MS to the target cell has been completed.

[0075] A computer program product includes a non-transitory computer-readable storage medium and storing executable code that, when executed by at least one data processing apparatus, is configured to cause the at least one data processing apparatus to perform a method including: transmitting, from the BS to a mobile station (MS), a handover command instructing the MS to perform a handover from the serving cell to the target cell, the handover command including at least a cell ID for the target cell, an identifier for the MS for the target cell, a time offset value for synchronizing the MS with the target cell, and a switch time indicator that indicates when the MS should switch to the target cell, the time offset value for the new cell for the MS being the same as a time offset value for the serving cell; and receiving, by the BS, a handover confirm message from the MS that confirms that the handover of the MS to the target cell has been completed. [0076] FIG. 6 is a flow chart illustrating operation of a base station (BS) according to an example implementation. The flow chart of FIG. 6 is directed to a method of synchronizing a handover for a group of mobile stations to a target cell. The method may include:

[0077] Operation 610 may include receiving, by a base station (BS), a

measurement report from each of a plurality of mobile stations (MSs) of a group of MSs for at least the target cell, each of the measurement reports indicating the target cell for handover.

[0078] Operation 620 may include transmitting, from the BS to each of the MSs of the group, a respective handover command instructing the MS to perform a handover to the target cell, each respective handover command including at least a cell ID for the target cell, an identifier for the MS for the target cell, a time offset value for synchronizing the MS with the target cell, and a switch time indicator that indicates when the MS should switch to the target cell, the time offset value for the new cell for the MS being the same as a time offset value for the serving cell for the MS, wherein the switch time indicator provided to each of the MSs of the group indicating a same time so as to synchronize the handovers of the MSs of the group.

[0079] In the method of FIG. 6, the method may further include receiving, by the BS, a handover confirm message from one or more of the MSs of the group that confirms that the handover of the MS to the target cell has been completed.

[0080] In the method of FIG. 6, each MS of the group may have a MS-specific time offset value for the target cell.

[0081] In the method of FIG. 6, the switch time indicator may include a

transmission time interval (TTI) for the target cell that indicates when the MS should switch to the target cell or a time the handover to the target cell is to be completed, and wherein the time offset value may include a timing advance for the MS for the target cell.

[0082] In the method of FIG. 6, the transmitting a respective handover command instructing the MS to perform a handover to the target cell may include transmitting, by the BS to each MS of the group, a RRCConnectionReconfiguration message with a

MobilityControllnfo information element that includes at least the cell ID for the target cell, the identifier for the MS for the target cell and a resource assignment for the MS for the target cell, the handover command also including the switch time indicator that indicates when the MS should switch to the target cell and the time offset value for the MS for the target cell.

[0083] According to another example implementation, an apparatus may include at least one processor and at least one memory including computer instructions, when executed by the at least one processor, cause the apparatus to: receive, by a base station (BS), a measurement report from each of a plurality of mobile stations (MSs) of a group of MSs for at least the target cell, each of the measurement reports indicating the target cell for handover; and transmit, from the BS to each of the MSs of the group, a respective handover command instructing the MS to perform a handover to the target cell, each respective handover command including at least a cell ID for the target cell, an identifier for the MS for the target cell, a time offset value for synchronizing the MS with the target cell, and a switch time indicator that indicates when the MS should switch to the target cell, the time offset value for the new cell for the MS being the same as a time offset value for the serving cell for the MS, wherein the switch time indicator provided to each of the MSs of the group indicating a same time so as to synchronize the handovers of the MSs of the group.

[0084] According to another example implementation, a computer program product may include a non-transitory computer-readable storage medium and storing executable code that, when executed by at least one data processing apparatus, is configured to cause the at least one data processing apparatus to perform a method including: receiving, by a base station (BS), a measurement report from each of a plurality of mobile stations (MSs) of a group of MSs for at least the target cell, each of the measurement reports indicating the target cell for handover; and transmitting, from the BS to each of the MSs of the group, a respective handover command instructing the MS to perform a handover to the target cell, each respective handover command including at least a cell ID for the target cell, an identifier for the MS for the target cell, a time offset value for synchronizing the MS with the target cell, and a switch time indicator that indicates when the MS should switch to the target cell, the time offset value for the new cell for the MS being the same as a time offset value for the serving cell for the MS, wherein the switch time indicator provided to each of the MSs of the group indicating a same time so as to synchronize the handovers of the MSs of the group.

[0085] FIG. 7 is a block diagram of a wireless station (e.g., BS or MS) 700 according to an example implementation. The wireless station 700 may include, for example, two RF (radio frequency) or wireless transceivers 702A, 702B, where each wireless transceiver includes a transmitter to transmit signals and a receiver to receive signals. The wireless station also includes a processor 704 to execute instructions or software and control transmission and receptions of signals, and a memory 706 to store data and/or instructions.

[0086] Processor 704 may also make decisions or determinations, generate frames, packets or messages for transmission, decode received frames or messages for further processing, and other tasks or functions described herein. Processor 704, which may be a baseband processor, for example, may generate messages, packets, frames or other signals for transmission via wireless transceiver 702. Processor 704 may control transmission of signals or messages over a wireless network, and may receive signals or messages, etc., via a wireless network (e.g., after being down-converted by wireless transceiver 702, for example). Processor 704 may be programmable and capable of executing software or other instructions stored in memory or on other computer media to perform the various tasks and functions described above, such as one or more of the tasks or methods described above. Processor 704 may be (or may include), for example, hardware, programmable logic, a programmable processor that executes software or firmware, and/or any combination of these. Using other terminology, processor 704 and transceiver 702 together may be considered as a wireless transmitter/receiver system, for example.

[0087] In addition, referring to FIG. 7, a controller (or processor) 708 may execute software and instructions, and may provide overall control for the station 700, and may provide control for other systems not shown in FIG. 7, such as controlling input/output devices (e.g., display, keypad), and/or may execute software for one or more applications that may be provided on wireless station 700, such as, for example, an email program, audio/video applications, a word processor, a Voice over IP application, or other application or software.

[0088] In addition, a storage medium may be provided that includes stored instructions, which when executed by a controller or processor may result in the processor 704, or other controller or processor, performing one or more of the functions or tasks described above.

[0089] Implementations of the various techniques described herein may be implemented in digital electronic circuitry, or in computer hardware, firmware, software, or in combinations of them. Implementations may implemented as a computer program product, i.e., a computer program tangibly embodied in an information carrier, e.g., in a machine-readable storage device or in a propagated signal, for execution by, or to control the operation of, a data processing apparatus, e.g., a programmable processor, a computer, or multiple computers. A computer program, such as the computer program(s) described above, can be written in any form of programming language, including compiled or interpreted languages, and can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. A computer program can be deployed to be executed on one computer or on multiple computers at one site or distributed across multiple sites and interconnected by a communication network.

[0090] Method steps may be performed by one or more programmable processors executing a computer program to perform functions by operating on input data and generating output. Method steps also may be performed by, and an apparatus may be implemented as, special purpose logic circuitry, e.g., an FPGA (field programmable gate array) or an ASIC (application-specific integrated circuit).

[0091] Processors suitable for the execution of a computer program include, by way of example, both general and special purpose microprocessors, and any one or more processors of any kind of digital computer. Generally, a processor will receive instructions and data from a read-only memory or a random access memory or both. Elements of a computer may include at least one processor for executing instructions and one or more memory devices for storing instructions and data. Generally, a computer also may include, or be operatively coupled to receive data from or transfer data to, or both, one or more mass storage devices for storing data, e.g., magnetic, magneto-optical disks, or optical disks. Information carriers suitable for embodying computer program instructions and data include all forms of non-volatile memory, including by way of example semiconductor memory devices, e.g., EPROM, EEPROM, and flash memory devices; magnetic disks, e.g., internal hard disks or removable disks; magneto-optical disks; and CD-ROM and DVD-ROM disks. The processor and the memory may be supplemented by, or incorporated in, special purpose logic circuitry.

[0092] To provide for interaction with a user, implementations may be

implemented on a computer having a display device, e.g., a cathode ray tube (CRT) or liquid crystal display (LCD) monitor, for displaying information to the user and a keyboard and a pointing device, e.g., a mouse or a trackball, by which the user can provide input to the computer. Other kinds of devices can be used to provide for interaction with a user as well; for example, feedback provided to the user can be any form of sensory feedback, e.g., visual feedback, auditory feedback, or tactile feedback; and input from the user can be received in any form, including acoustic, speech, or tactile input.

[0093] Implementations may be implemented in a computing system that includes a back-end component, e.g., as a data server, or that includes a middleware component, e.g., an application server, or that includes a front-end component, e.g., a client computer having a graphical user interface or a Web browser through which a user can interact with an implementation, or any combination of such back-end, middleware, or front-end components. Components may be interconnected by any form or medium of digital data communication, e.g., a communication network. Examples of communication networks include a local area network (LAN) and a wide area network (WAN), e.g., the Internet.

[0094] While certain features of the described implementations have been illustrated as described herein, many modifications, substitutions, changes and equivalents will now occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the various embodiments.

Claims

WHAT IS CLAIMED IS:

1. A method comprising:

performing, by a mobile station (MS), a random access-free and intra-base station (BS) handover from a serving cell to a target cell by the MS using a time offset value for synchronization with the target cell that was used by the MS for the serving cell, both the serving cell and the target cell being provided by a same BS and antenna system.

2. The method of claim 1 wherein the intra-BS handover is performed as a synchronized group handover to the target cell that is created based on cell splitting.

3. The method of claim 2 wherein MSs outside of the serving cell are prevented from performing a handover to the target cell between a time the target cell is activated until the synchronized group handover to the target cell is completed.

4. The method of claim 1 wherein the intra-BS handover is performed as a synchronized group handover to the target cell based deactivating the serving cell as part of cell merging.

5. The method of claim 4 wherein MSs are prevented from performing a handover to the serving cell after the synchronized group handover of all MSs in the serving cell to the target cell is completed.

6. The method of claim 1 wherein the performing the random access-free and intra-BS handover comprises:

determining, by the MS, a time offset value used by the MS for the serving cell;

receiving, by the MS, a handover command from the BS instructing the MS to perform a handover from the serving cell to the target cell, the handover command providing handover information including at least a cell ID for the target cell, an identifier for the MS for the target cell, a resource assignment for the target cell, and a switch time indicator that indicates when the MS should switch to the target cell; sending, based on the handover information received by the MS and the time offset value, a handover confirm message from the MS to the BS to confirm that the handover of the MS to the target cell has been completed.

7. The method of claim 6 and further comprising: receiving, by the MS from the BS in the handover command, a time offset value for the target cell, the time offset for the target cell for the MS being the same as the time offset value for the serving cell for the MS based at least in part on the same BS and antenna system being used to provide both the serving cell and the target cell.

8. The method of claim 6 and further comprising:

receiving, by the MS, a measurement configuration message from the serving cell instructing the MS to measure signal strength and/or quality for each of one or more listed cells, the listed cells including the target cell that was added based on cell deployment changes; measuring, by the MS, a reference signal of at least the target cell; and sending, by the MS, a measurement report for at least the target cell to the BS, the measurement report indicating the target cell for handover.

9. The method of claim 8 wherein the receiving the measurement configuration message comprises receiving RRCConnectionReconfiguration message including a MeasConfig information element.

10. The method of claim 6 wherein the switch time indicator comprises a transmission time interval (TTI) for the target cell that indicates a time the handover to the target cell is to be completed.

1 1 . The method of claim 6 wherein the receiving a handover command comprises receiving, by the MS, a RRCConnectionReconfiguration message with a

MobilityControllnfo information element that includes at least the cell I D for the target cell, the identifier for the MS for the target cell and the resource assignment for the target cell, the handover command also including the switch time indicator that indicates when the MS should switch to the target cell and a time offset value for the MS for the target cell.

12. The method of claim 6 wherein the receiving a handover confirm message comprises receiving a RRCConnectionReconfigurationComplete message.

13. An apparatus comprising at least one processor and at least one memory including computer instructions, when executed by the at least one processor, cause the apparatus to perform, by a mobile station (MS), a random access-free and intra-base station (BS) handover from a serving cell to a target cell by the MS using a time offset value for synchronization with the target cell that was used by the MS for the serving cell, both the serving cell and the target cell being provided by a same BS and antenna system, the apparatus being caused to perform includes the apparatus being caused to: determine, by the MS, a time offset value used by the MS for the serving cell; receive, by the MS, a handover command from the BS instructing the MS to perform a handover from the serving cell to the target cell, the handover command including at least a cell ID for the target cell, an identifier for the MS for the target cell, and a switch time indicator that indicates when the MS should switch to the target cell; send, based on the handover information received by the MS and the time offset value, a handover confirm message from the MS to the BS to confirm that the handover of the MS to the target cell has been completed.

14. The apparatus of claim 13 wherein the apparatus is further caused to:

receive, by the MS from the BS in the handover command, a time offset value for the target cell, the time offset for the target cell for the MS being the same as a time offset value for the serving cell for the MS based at least in part on the same BS and antenna system being used to provide both the serving cell and the target cell.

15. The apparatus of claim 13 wherein the switch time indicator comprises a transmission time interval (TTI) for the target cell that indicates when the MS should switch to the target cell or a time the handover to the target cell is to be completed, and wherein the time offset value comprises a timing advance for the MS for the target cell.

16. A computer program product, the computer program product comprising a non- transitory computer-readable storage medium and storing executable code that, when executed by at least one data processing apparatus, is configured to cause the at least one data processing apparatus to perform a method comprising:

17. The computer program product of claim 16 wherein the performing the random access-free and intra-BS handover comprises:

determining, by the MS, a time offset value used by the MS for the serving cell; receiving, by the MS, a handover command from the BS instructing the MS to perform a handover from the serving cell to the target cell, the handover command providing handover information including at least a cell ID for the target cell, an identifier for the MS for the target cell, a resource assignment for the target cell, and a switch time indicator that indicates when the MS should switch to the target cell; and

sending, based on the handover information received by the MS and the time offset value, a handover confirm message from the MS to the BS to confirm that the handover of the MS to the target cell has been completed.

18. A method of facilitating a random access-free and intra-base station handover from a serving cell to a target cell, both the serving cell and the target cell being provided by a same base station (BS) and antenna system, the method comprising:

transmitting, from the BS to a mobile station (MS), a handover command instructing the MS to perform a handover from the serving cell to the target cell, the handover command including at least a cell ID for the target cell, an identifier for the MS for the target cell, a time offset value for synchronizing the MS with the target cell, and a switch time indicator that indicates when the MS should switch to the target cell, the time offset value for the new cell for the MS being the same as a time offset value for the serving cell; and receiving, by the BS, a handover confirm message from the MS that confirms that the handover of the MS to the target cell has been completed.

19. The method of claim 18 wherein the switch time indicator comprises a transmission time interval (TTI) for the target cell that indicates when the MS should switch to the target cell or a time the handover to the target cell is to be completed, and wherein the time offset value comprises a timing advance for the MS for the target cell.

20. The method of claim 18 wherein the transmitting a handover command comprises transmitting, by the BS, a RRCConnectionReconfiguration message with a MobilityControllnfo information element that includes at least the cell ID for the target cell, the identifier for the MS for the target cell and a resource assignment for the target cell, the handover command also including the switch time indicator that indicates when the

MS should switch to the target cell and the time offset value for the MS for the target cell.

21 . An apparatus comprising at least one processor and at least one memory including computer instructions, when executed by the at least one processor, cause the apparatus to: transmitting, from the BS to a mobile station (MS), a handover command instructing the MS to perform a handover from the serving cell to the target cell, the handover command including at least a cell ID for the target cell, an identifier for the MS for the target cell, a time offset value for synchronizing the MS with the target cell, and a switch time indicator that indicates when the MS should switch to the target cell, the time offset value for the new cell for the MS being the same as a time offset value for the serving cell; and receiving, by the BS, a handover confirm message from the MS that confirms that the handover of the MS to the target cell has been completed.

22. A computer program product, the computer program product comprising a non- transitory computer-readable storage medium and storing executable code that, when executed by at least one data processing apparatus, is configured to cause the at least one data processing apparatus to perform a method comprising:

23. A method of synchronizing a handover for a group of mobile stations to a target cell, the method comprising:

receiving, by a base station (BS), a measurement report from each of a plurality of mobile stations (MSs) of a group of MSs for at least the target cell, each of the measurement reports indicating the target cell for handover; and transmitting, from the BS to each of the MSs of the group, a respective handover command instructing the MS to perform a handover to the target cell, each respective handover command including at least a cell ID for the target cell, an identifier for the MS for the target cell, a time offset value for synchronizing the MS with the target cell, and a switch time indicator that indicates when the MS should switch to the target cell, the time offset value for the new cell for the MS being the same as a time offset value for the serving cell for the MS, wherein the switch time indicator provided to each of the MSs of the group indicating a same time so as to synchronize the handovers of the MSs of the group.

24. The method of claim 23 and further comprising receiving, by the BS, a handover confirm message from one or more of the MSs of the group that confirms that the handover of the MS to the target cell has been completed.

25. The method of claim 23, wherein each MS of the group has a MS-specific time offset value for the target cell.

26. The method of claim 23 wherein the switch time indicator comprises a transmission time interval (TTI) for the target cell that indicates when the MS should switch to the target cell or a time the handover to the target cell is to be completed, and wherein the time offset value comprises a timing advance for the MS for the target cell.

27. The method of claim 23 wherein the transmitting a respective handover command instructing the MS to perform a handover to the target cell comprises transmitting, by the BS to each MS of the group, a RRCConnectionReconfiguration message with a MobilityControllnfo information element that includes at least the cell ID for the target cell, the identifier for the MS for the target cell and a resource assignment for the MS for the target cell, the handover command also including the switch time indicator that indicates when the MS should switch to the target cell and the time offset value for the MS for the target cell.

28. An apparatus comprising at least one processor and at least one memory including computer instructions, when executed by the at least one processor, cause the apparatus to:

receive, by a base station (BS), a measurement report from each of a plurality of mobile stations (MSs) of a group of MSs for at least the target cell, each of the measurement reports indicating the target cell for handover; and transmit, from the BS to each of the MSs of the group, a respective handover command instructing the MS to perform a handover to the target cell, each respective handover command including at least a cell ID for the target cell, an identifier for the MS for the target cell, a time offset value for synchronizing the MS with the target cell, and a switch time indicator that indicates when the MS should switch to the target cell, the time offset value for the new cell for the MS being the same as a time offset value for the serving cell for the MS, wherein the switch time indicator provided to each of the MSs of the group indicating a same time so as to synchronize the handovers of the MSs of the group.

29. A computer program product, the computer program product comprising a non- transitory computer-readable storage medium and storing executable code that, when executed by at least one data processing apparatus, is configured to cause the at least one data processing apparatus to perform a method comprising: