Abstract:
Systems and methods for reduction of handover latencies in wireless communication systems are described herein. Some illustrative embodiments include a wireless mobile communication device that includes a wireless transceiver including a transmitter configured to transmit a first signal synchronized for reception by a first cellular node, and processing logic that couples to the wireless transceiver. Before the wireless transceiver receives a handover command the processing logic causes the transmitter to transmit a second signal for reception by a second cellular node to request allocation of an upload resource for communication with the second cellular node as part of an impending handover.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims the benefits of provisional application Ser. No. 60/805,261, filed Jun. 20, 2006 and entitled “Reducing Handover Latencies Using Early RACH Access in 3GPP LTE,” provisional application Ser. No. 60/805,306, filed Jun. 20, 2006 and entitled “Reducing Handover Latencies Using Early RACH Access in 3GPP LTE,” and provisional application Ser. No. 60/805,429, filed Jun. 21, 2006 and entitled “Reducing Handover Latencies Using Early RACH Access in 3GPP LTE,” all of which are herein incorporated by reference. 
    
    
     BACKGROUND 
     The use of mobile communication devices has increased dramatically in recent years. These mobile devices include devices that communicate with a network of wireless transceivers or base stations, which are organized as an array of geographic service areas or “cells.” An example of this type of wireless network is a cellular network used in conjunction with a mobile or cellular telephone. A cell can be defined as a limited geographic area completely surrounding the antenna of a base station that uses an omnidirectional antenna covering a full 360 degrees. A cell may also be defined as a portion of a geographic area surrounding a base station that uses multiple directional antennas that each covers less than 360 degrees (e.g., 4 antennas each covering 90 degrees or more, thus each defining a cell). 
     Whenever a user of a mobile device approaches a boundary between two cells (which includes some overlap between the cells), communications between the mobile device and the communication network may be transferred from one cell to another, depending on the relative strength of the cellular transmitters of each cell&#39;s base station. This transfer or “handover” involves command and data exchanges between the mobile device and each base station, as well as between the base stations. Such exchanges utilize a percentage of the bandwidth needed for general communications, and thus represent an overhead cost of operating the network. The actual handover also takes a certain amount of time to complete, introducing small delays and potentially a momentary interruption in the data exchanges between the mobile device and the network. With the increased use of mobile devices in video and high-speed data applications, and with the increased demand for base stations and networks that can support larger numbers of mobile devices, these delays or “latencies” introduced during handovers may decrease the performance of the base stations and the overall network to unacceptable levels. 
     SUMMARY 
     Systems and methods for reduction of handover latencies in wireless communication systems are described herein. Some illustrative embodiments include a wireless mobile communication device that includes a wireless transceiver including a transmitter configured to transmit a first signal synchronized for reception by a first cellular node, and processing logic that couples to the wireless transceiver. Before the wireless transceiver receives a handover command the processing logic causes the transmitter to transmit a second signal for reception by a second cellular node to request allocation of an upload resource for communication with the second cellular node as part of an impending handover. 
     Other illustrative embodiments include a plurality of cellular nodes that each includes a wireless transceiver including a transmitter and a receiver (configured to transmit signals to, and receive signals from, a wireless mobile communication device), and processing logic that couples to the wireless transceiver. Before the processing logic of a first cellular node of the plurality of cellular nodes causes its transmitter to transmit a handover command, the receiver of a second cellular node of the plurality of cellular nodes receives a request to allocate an upload resource as part of an impending handover. 
     Yet further illustrative embodiments include a method that includes a target cellular node within a wireless communication system receiving a request to allocate an upload resource as part of an impending handover; the target cellular node, in response to the request to allocate the upload resource, transmitting a message comprising synchronization and resource allocation information; and a source cellular node transmitting a handover command after the receiving by the target cellular node the request to allocate the upload resource. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a detailed description of illustrative embodiments of the invention, reference will now be made to the accompanying drawings in which: 
         FIG. 1  shows a wireless communication system including two base stations and a mobile communication device, all constructed in accordance with at least some illustrative embodiments; 
         FIG. 2  shows the distribution of cells within and between base stations constructed in accordance with at least some illustrative embodiments; 
         FIG. 3   a  shows an example of a system configuration, suitable for use as a wireless communications system cellular node, in accordance with at least some illustrative embodiments; 
         FIG. 3   b  shows a block diagram of the system configuration of  3   a , in accordance with at least some illustrative embodiments; 
         FIG. 4   a  shows an example of a system configuration, suitable for use as a mobile communication device, in accordance with at least some illustrative embodiments; 
         FIG. 4   b  shows a block diagram of the system configuration of  4   a , in accordance with at least some illustrative embodiments; 
         FIG. 5   a  shows a handover sequence between two cellular nodes and a mobile communication device triggered by a handover decision message from a cellular node, in accordance with at least some illustrative embodiments; and 
         FIG. 5   b  shows a handover sequence between two cellular nodes and a mobile communication device triggered by a handover prediction by a mobile communication device, in accordance with at least some illustrative embodiments; 
         FIG. 6   a  shows a method for performing a reduced latency handover of a mobile communication device between two cellular nodes triggered by a handover decision message from a cellular node, in accordance with at least some illustrative embodiments; and 
         FIG. 6   b  shows a method for performing a reduced latency handover of a mobile communication device between two cellular nodes triggered by a handover prediction by a mobile communication device, in accordance with at least some illustrative embodiments. 
     
    
    
     NOTATION AND NOMENCLATURE 
     Certain terms are used throughout the following discussion and claims to refer to particular system components. This document does not intend to distinguish between components that differ in name but not function. In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including but not limited to . . . .” Also, the term “couple” or “couples” is intended to mean either an indirect or direct electrical connection. Thus, if a first device couples to a second device, that connection may be through a direct electrical connection, or through an indirect electrical connection via other devices and connections. Additionally, the term “system” refers to a collection of two or more hardware and/or software components and may be used to refer to an electronic device, such as a mobile wireless communication device or a cellular node, a portion of a mobile wireless communication device or cellular node, mobile wireless communication devices and/or cellular nodes, etc. Further, the term “software” includes any executable code capable of running on a processor, regardless of the media used to store the software. Thus, code stored in non-volatile memory, and sometimes referred to as “embedded firmware,” is included within the definition of software. 
     DETAILED DESCRIPTION 
     The following discussion is directed to various embodiments of the invention. Although one or more of these embodiments may be preferred, the embodiments disclosed should not be interpreted, or otherwise used, as limiting the scope of the disclosure, including the claims, unless otherwise specified. The discussion of any embodiment is meant only to be illustrative of that embodiment, and not intended to intimate that the scope of the disclosure, including the claims, is limited to that embodiment. 
       FIG. 1  shows a portion of a communications network  100  that includes base stations  200  and  250 , each constructed in accordance with at least some illustrative embodiments. The base stations shown are part of a terrestrial communication network used by mobile communication device  400 , also constructed in accordance with at least some illustrative embodiments, to access the communications network  100 . Each base station includes one or more antennas and corresponding receivers that each defines a transmission coverage area known as a “cell.” Thus, each base station may have one or more “cellular nodes,” each with a transceiver and antenna that provides communications for a given cell. Wireless mobile communication device  400  communicates with a cellular node through a given antenna based upon the cell within which the wireless mobile communication device  400  is located. 
       FIG. 2  shows the coverage areas of the cells defined by each of the antennas shown in  FIG. 1 . The antennas  202  mounted on tower  212  each define a pie shaped cell emanating from each antenna (Cells  1  through  4 ). The antenna  252  mounted on tower  262  defines a single cell (Cell  5 ) covering a full 360 degrees around the tower. The cells overlap in order to allow uninterrupted communications as the wireless mobile communication device  400  is moved between the coverage areas defined by the cellular nodes. When wireless mobile communication device  400  approaches a boundary of one cell (the “source” cell) while moving towards the antenna of another cell (the “target” cell), a decision is made by processing logic controlling a transceiver coupled to the source cell antenna to transfer responsibility for communications with wireless mobile communication device  400  and execute a “handover.” The handover of wireless mobile communication device  400  results in communications between the device and communications network  100  being routed through the target cell instead of the source cell. The processing system controlling a transceiver coupled to the target antenna assumes command, control and data routing functions previously performed by the processing system of the source cell. 
       FIGS. 3   a  and  3   b  show an illustrative system configuration  300  suitable for implementing a cellular node processing system within the base stations  200  and  250  of  FIG. 1 . As shown in  FIG. 3   a , the illustrative system configuration  300  includes a chassis  302 , a display  304  and an input device (e.g., a keyboard)  306 . The system configuration  300 , as shown in  FIG. 3   b , further includes processing logic  330  (e.g., a microprocessor), non-volatile storage  332 , and volatile storage  334 . Non-volatile storage  332  includes a computer-readable medium such as a flash random access memory (flash RAM), a read-only memory (ROM), a hard disk drive, a floppy disk (e.g., floppy  370 ), a compact disk read-only memory (CD-ROM, e.g., CD-ROM  360 ), as well as combinations of some and/or all such medium. Volatile storage  334  includes a computer readable medium such as random access memory (RAM). 
     The computer readable media of both non-volatile storage  332  and volatile storage  334  include, for example, software that is executed by processing logic  330  and provides each cellular node with at least some of the functionality described herein. The system configuration  300  also includes a network interface (Network I/F)  326  that enables the system configuration  300  to transmit information to, and receive information from, a local area network (LAN) and/or a wide area network (WAN), represented in the example of  FIG. 3   a  by Ethernet jack  308 . A transceiver interface (Xcvr I/F)  328  provides an interface to wireless transceiver  338 , which provides system configuration  300  with the capability of communicating wirelessly with one or more wireless mobile devices via at least one of antennas  340 . A graphics interface (Graphics I/F)  322  couples to the display  304 . A user interacts with the processing system via an input device such as keyboard  306  and/or pointing device (Pointing Dev)  336  (e.g., a mouse), which couples to a peripheral interface (Peripheral I/F)  324 . The display  304 , keyboard  306  and pointing device  336  together may operate as a user interface. 
     System configuration  300  may be a bus-based computer, with the bus  320  interconnecting the various elements shown in  FIG. 3   b . The peripheral interface  324  accepts signals from the keyboard  306  and other input devices such as pointing device  336 , and transforms the signals into a form suitable for communication on bus  320 . The graphics interface  322  may include a video card or other suitable display interface that accepts information from the bus  320  and transforms it into a form suitable for the display  304 . Similarly, transceiver interface  328  accepts signals from wireless transceiver  338  and transforms them into a form suitable for communication on bus  320 , and further accepts information from bus  320  and transforms it into a form suitable for wireless transceiver  338 . 
     Although the illustrative embodiment of  FIGS. 3   a  and  3   b  show transceiver  338  as a hardware element that is separate from system configuration  300 , other embodiments may incorporate the hardware of transceiver  338  as part of system configuration  300 . In still other illustrative embodiments, at least some of the functionality of transceiver  338  may be implemented as software executed by processing logic  330 . Other combinations of hardware and software, both integral and external to system configuration  300 , which implement the functionality of transceiver  338  will become apparent to those skilled in the art, and all such combinations are within the scope of the present disclosure. 
     Processing logic  330  gathers information from other system elements, including input data from the peripheral interface  324 , wireless communication data from transceiver interface  328 , and program instructions and other data from non-volatile storage  332  or volatile storage  334 , or from other systems (e.g., a server used to store and distribute copies of executable code) coupled to a local area network or a wide area network via the network interface  326 . Processing logic  330  executes the program instructions and processes the data accordingly. The program instructions may further configure processing logic  330  to send data to other system elements, such as information presented to the user via the graphics interface  322  and display  304 , and wireless communication data transmitted via transceiver interface  328  and wireless transceiver  338 . The network interface  326  enables processing logic  330  to communicate with other systems via a network. Volatile storage  334  may serve as a low-latency temporary store of information for processing logic  330 , and non-volatile storage  332  may serve as a long-term (but higher latency) store of information. 
     Processing logic  330 , and hence the system configuration  300  as a whole, operates in accordance with one or more programs stored on non-volatile storage  332  or received via network interface  326 . Processing logic  330  may copy portions of the programs into volatile storage  334  for faster access, and may switch between programs or carry out additional programs in response to user actuation of the input devices. The additional programs may be retrieved or received from other locations via network interface  326 . One or more of these programs executes on system configuration  300 , causing the configuration to perform at least some of the functions of a cellular node as disclosed herein. 
       FIGS. 4   a  and  4   b  show an illustrative system suitable for implementing the wireless mobile communication device  400  of  FIG. 1 . As shown in  FIG. 4   a , wireless mobile communication device  400  includes a display  406 , a keypad  408 , a wireless transceiver  404  with an antenna  402 , and a processing subsystem  450 . The processing subsystem  450 , which may be implemented as a system-on-a-chip (SoC), further includes processing logic  414  (e.g., an ARM processor core), and memory  416  that may include both non-volatile and volatile storage in the form of computer-readable medium such as ROM, flash RAM and RAM. 
     The computer readable media of memory  416  includes, for example, software that is executed by processing logic  414  and provides the wireless mobile communication device  400  with at least some of the functionality described herein. The processing subsystem  450  also includes an analog interface (Analog I/F)  422  that sends audio to, and receives audio from, a user of the wireless mobile communication device  400 , via speaker  410  and microphone (Mic)  412  respectively. Wireless transceiver  404  provides wireless mobile communication device  400  with the capability of communicating wirelessly with one or more cellular nodes via antenna  402 . Processing subsystem  450  also includes a graphics controller  418  that couples to the display  406 . A user interacts with the processing subsystem via an input device such as keypad  408 , which couples to serial input/output interface (Serial I/O I/F)  420 . The display  406  and keypad  408  together may operate as a user interface. 
     Serial input/output interface  420  accepts signals from the keypad  408  and transforms the signals into a form suitable for processing logic  414 . The graphics controller  418  accepts information from the processing logic  414  and transforms it into a form suitable for the display  406 . Similarly, wireless transceiver  404  receives signals from one or more cellular nodes via antenna  402  and transforms them into a form suitable for processing logic  414 , and further accepts information from processing logic  414  and transforms it into a form suitable for transmission to one or more cellular nodes by wireless transceiver  404 . The information sent and received by wireless transceiver  404  includes voice and other user data, command and control information used to configure and operate the wireless mobile communication device  400 , and program instructions that can be executed by processing logic  414 . 
     Processing logic  414  gathers information from other system elements, including input data from the serial input/output interface  420 , wireless communication information from wireless transceiver  404 , and program instructions and other data from memory  416  or from other systems (e.g., a server used to store and distribute copies of executable code) coupled to a wide area network and that communicate with wireless mobile communication device  400  via the wireless transceiver  404 . Processing logic  414  executes the program instructions and processes the data accordingly. The program instructions may further configure processing logic  414  to send data to other system elements, such as information presented to the user via the graphics controller  418  and display  406 , audio presented to the user via analog interface  422  and speaker  410 , and wireless communication data transmitted via wireless transceiver  404  and antenna  402 . Wireless transceiver  404  also enables processing logic  414  to communicate with other systems. Memory  416  may provide both volatile storage for low-latency temporary storage of information for processing logic  414 , as well as non-volatile storage for long-term (but higher latency) storage of information. 
     Processing logic  414 , and hence the wireless mobile communication device  400  as a whole, operates in accordance with one or more programs stored in memory  416  or received via wireless transceiver  404 . Processing logic  414  may copy portions of the programs within memory  416  from non-volatile storage into volatile storage for faster access, and may switch between programs or carry out additional programs in response to user actuation of the keypad. The additional programs may be retrieved or received from other locations via wireless transceiver  404 . One or more of these programs executes on processing subsystem  450 , causing the subsystem to perform at least some of the functions of wireless mobile communication device  400  as disclosed herein. 
     In at least some illustrative embodiments, wireless mobile communication device  400  transmits and receives data via a plurality of cellular nodes such as those within base stations  200  and  250  of  FIG. 1 , each cellular node including a system configuration  300  as previously described. The data exchanged may be voice data, used by wireless mobile communication device  400  to provide a user of the device with voice communications with other users of similar wireless mobile communication devices, or may be other data, such as data originating from a server on the Internet and provided to the user via the display of the wireless mobile communication device  400 . Regardless of the type of data, its origin, or its destination, the data is provided to and from wireless mobile communication device  400  via cellular nodes within base stations similar to base stations  200  and/or  250 . 
     As wireless mobile communication device  400  is moved from one location to another, the device may reach the range limits of a cell (see  FIG. 2 ), necessitating a handover of communications with the device from one cellular node to another. This cell-to-cell handover may be between cells under the control of a single base station with multiple cellular nodes, or cells under the control of cellular nodes within different base stations. Once a determination that a handover is needed has been made, the wireless mobile communication device attempts to secure a new communication link with the new or target cellular node before moving out of range of the current or source cellular node. Failure to establish communications with the target cellular node before communication with the source cellular node is lost can result in an interruption in an ongoing data exchange (e.g., a dropped telephone call). Such interruptions can result from the time delay or latency between determining the need for a handover and actually establishing a link between the wireless mobile device and the target cellular node. 
       FIGS. 5   a  and  5   b  show two examples of handover sequences ( 500   a  and  500   b ) that reduce the above described latency, in accordance with at least some illustrative embodiments. Referring to  FIG. 5   a , communications between each of a wireless mobile communication device (Mobile)  502 , source cellular node (Source Node)  504  and target cellular node (Target Node)  506  are indicated in the horizontal direction, and time is shown progressing from vertically from top to bottom. The handover sequence begins when handover decision  512  is made by logic within Source Node  504  (e.g., processing logic  330  of system configuration  300  of  FIG. 3   b ). The decision can be made, for example, based upon diminishing signal strength of one cellular node and increasing signal strength of another cellular node, as reported by Mobile  502  to Source Node  504 . 
     Continuing to refer to  FIG. 5   a , once the handover decision has been made, handover decision message (HO Decision Message)  522  is transmitted by Source Node  504  to Mobile  502 . In at least some illustrative embodiments, handover decision message  522  is transmitted over an existing download communication resource between Source Node  504  and Mobile  502 . For purposes of this discussion, a communication resource (herein after, “Resource”) represents a portion of the overall channel capacity used for communication, to be used over one or more specific time intervals. Such Resource allocations may include, for example, a subdivision of a spectrum (e.g., a range of radio frequencies) used for transmitting and receiving information. Such Resource allocations may also include, for example, subdivisions in time and/or frequency, or distinct codes used concurrently across time and/or frequency (e.g., codes such as those used in Code Division Multiple Access communications). Further, data flows across a download Resource from a cellular node to Mobile  502 , and across an upload Resource from Mobile  502  to a cellular node. After receiving handover decision message  522 , Mobile  502  initiates a synchronization and upload Resource allocation request sequence. The synchronization process, as is known in the art, is a process by which a wireless mobile communication device, such as Mobile  502 , adjusts its transmitted signal such that the data sequence is properly aligned with the receiver of the cellular node with which the Mobile is communicating via an upload Resource. The adjustment or “timing advance” is designed to compensate for the propagation delay of the signal transmitted by Mobile  502 , which will vary depending upon the distance to the cellular node receiving the signal. 
     Mobile  502  request access to Target Node  506  by sending synchronization and upload Resource allocation request (Access Request)  524  to Target Node  506 . In at least some illustrative embodiments, a random access channel (RACH) is used by Mobile  502  to send the request. As is known in the art, a random access channel is a general purpose upload Resource periodically made available by a cellular node for use by any wireless mobile communication device that requires it. Once Target Node  506  has processed the Access Request from Mobile  502  and allocated one or more upload Resources, Target Node  506  sends the upload Resource allocation(s) and timing advance information (UL Allocation and TA Info)  526  to Mobile  502 . With the allocation of the upload Resource, Mobile  502  has one or more allocated resources with Target Node  506  which can be used to communicate with Target Node  506  once the handover command is issued. More than one resource can be allocated (e.g., 3 upload resources) and can be spread out over time such that at least one allocated resource is available late enough in time for use by Mobile  502  after receipt of a possibly delayed handover command. In at least some illustrative embodiments, the upload Resource allocation(s) and timing advance information is forwarded or relayed by Source Node  504  from Target Node  506  to Mobile  502  (not shown). 
     Sometime after the Access Request is initiated by Mobile  502 , Source Node  504  sends handover command  528  to Mobile  502 , and Mobile  502  detaches from Source Node  504  (block  514 ). The handover command may be issued by Source Node  504  anywhere within a time period spanning before and after the upload Resource allocation(s) and timing advance information is sent to Mobile  502 , as shown by the two HO Command arrows  528  and the shaded area in between them. However because the process of establishing an upload path between Mobile  502  and Target Node  506  has already been started and possibly completed and does not depend upon receipt of the handover command, Mobile  502  may begin to communicate with Target Node  506  sooner when compared to systems that do not issue an Access Request until after receiving the handover command. Thus, by not waiting for the handover command to issue to establish an upload Resource between Mobile  502  and Target  506 , the latency between the handover decision and the completion of the actual handover may be reduced. 
     The illustrative embodiment of  5   b  is similar to that of  5   a , but instead of waiting for the handover decision message to be transmitted by Source Node  504  before initiating the synchronization and upload Resource allocation sequence, Mobile  502  instead sends the Access Request based upon an internally generated handover prediction (block  510 ,  FIG. 5   b ). The prediction may be generated, for example, by an embodiment of Mobile  502  such as that of  FIG. 4B , wherein software executing within processing subsystem  450  produces the prediction. Such a prediction can be generated, for example, based upon signal strength and interference measurements logged by Mobile  502 . 
     Continuing to refer to  FIG. 5   b , once the handover prediction is made, Mobile  502  sending Access Request  524  to Target Node  506 . The request is made before handover decision  512  is made and before handover decision message  522  is sent by Source Node  504  to Mobile  502 . Both the decision  512  and the message  522  are shown in  FIG. 5   b  with dashed lines, reflecting the fact that the decision and message are ignored by Mobile  502  as it relates to the handover sequence  500   b . Target Node  506  responds to Access Request  524  by sending Mobile  502  upload Resource allocation(s) and timing advance information (UL Allocation and TA Info)  526  (either directly as shown in  FIG. 5   b , or indirectly via Source Node  504 ). The response may occur either before or after either handover decision  512  and handover decision message  522 , as indicated by the two arrows  526  and the shaded area in between them. In at least some illustrative embodiments, the handover decision message  522  is not transmitted to Mobile  502  by Source Node  504 . Continuing to refer to the illustrative embodiment of  FIG. 5   a , Source Node  504  issues handover command  528  to Mobile  502 , and Mobile  502  then detaches from Source Node  504  (block  514 ). The handover command may be issued by Source Node  504  anywhere within a time period spanning before and after the upload Resource allocation(s) and timing advance information is sent to Mobile  502 , as shown by the two HO Command arrows  528  and the shaded area in between them. In this manner the sequence of  FIG. 5   b  can provide additional reductions in latency over the sequence of  FIG. 5   a , given that Access Request  524  is initiated without waiting for handover decision  512 , thus providing even more time to setup the upload Resource with Target Node  506 . 
       FIG. 6   a  shows a method implementing the sequence of  FIG. 5   a , in accordance with at least some illustrative embodiments. Referring to both  FIGS. 5   a  and  6   a , the handover decision is made in block  602 , and a handover decision message is sent by Source Node  504  to Mobile  502  (block  604 ). The retry counter and wait timer are then reset (block  608 ) and Mobile  502  sends an Access Request to Target Node  506  (block  610 ). In at least some illustrative embodiments, the Source Node  504  transmits the handover command (block  612   a ) before allocation of the requested upload Resource(s) is checked in block  616 . If the upload Resource(s) is/are allocated and the timing advance information is provided (as indicated by UL Allocation and TA info  526  provided to Mobile  502  as shown in  FIG. 5   a ) before a timeout occurs (block  616 ), Mobile  502  detaches from Source Node  504  (block  626 ) completing the method (block  628 ). In at least some illustrative embodiments, the Source Node  504  transmits the handover command (block  612   b ) after the requested upload Resource(s) is/are allocated, but before the Mobile detaches from the Source Node  504 . The timeout referred to in block  616  is indicative of a failure to receive UL Allocation and TA info  526  of  FIG. 5   a  within a predetermined maximum time limit. If the upload Resource allocation is not completed before the maximum time limit (a timeout), the upload Resource allocation request is repeated. 
     Continuing to refer to  FIG. 6   a , if the upload Resource allocation is not completed before a timeout (block  616 ) and too many attempts at requesting an upload resource allocation have been made (too many retries, block  618 ), the handover is aborted and the method ends (block  628 ). If the retry limit (e.g., 3 retries) has not been exceeded, the Access Request is again sent to Target Node  506  (block  610 ) after a wait delay (block  620 ). In at least some illustrative embodiments, the wait delay is initialized at zero or a constant value (block  608 ) and incremented after each attempt when the retry counter is incremented (block  622 ). 
       FIG. 6   b  shows a method implementing the sequence of  FIG. 5   b , in accordance with at least some illustrative embodiments. Referring to both  FIGS. 5   b  and  6   b , the handover decision is predicted by Mobile  502  in block  601 , and the retry counter and wait timer are reset (block  608 ). Mobile  502  sends an Access Request to Target Node  506  (block  610 ). In at least some illustrative embodiments, the Source Node  504  transmits the handover command (block  612   a ) before allocation of the requested Resource(s) is/are provided by Target Node  506  to Mobile  502 . If the upload Resource(s) is/are allocated and the timing advance information is received (as indicated by UL Allocation and TA info  526  provided to Mobile  502  as shown in  FIG. 5   b ) before a timeout occurs (block  616 ), Mobile  502  detaches from Source Node  504  (block  626 ) completing the method (block  628 ). In at least some illustrative embodiments, the Source Node  504  transmits the handover command (block  612   b ) after the requested upload Resource(s) is/are allocated, but before the Mobile detaches from the Source Node  504 . 
     If receipt of the upload Resource allocation(s) and timing advance information is not completed before a timeout (block  616 ) and too many attempts at requesting an upload resource allocation have been made (too many retries, block  618 ), the handover is aborted and the method ends (block  628 ). If the retry limit (e.g., 3 retries) has not been exceeded, the Access Request is again sent to Target Node  506  (block  610 ) after a wait delay (block  620 ). In at least some illustrative embodiments, the wait delay is initialized at zero or a constant value (block  608 ) and incremented after each attempt when the retry counter is incremented (block  622 ). 
     The above disclosure is meant to be illustrative of the principles and various embodiments of the present invention. Numerous variations and modifications will become apparent to those skilled in the art once the above disclosure is fully appreciated. For example, although the embodiments described are illustrated within the context of a wireless radio frequency network using antennas, other embodiments using alternative wireless technologies (e.g., optical wireless technologies) are within the scope of the present disclosure. It is intended that the following claims be interpreted to embrace all such variations and modifications.