Various communication systems may benefit from mechanisms for transferring control over or communication with terminal devices. For example, certain wireless communication systems may benefit from a handover mechanism with pre-scheduling consecutive grants and pre-calculated timing advance.
Random access channel (RACH) based contention-free handover as designed in the third generation partnership project (3GPP) includes two steps. In the first step, a user equipment (UE) sends a preamble-index on physical random access channel (PRACH) to Target eNB. In the second step, the target eNB replies to the UE with an uplink grant and timing advance (TA). Only after these two steps, UE can start to send the first uplink packet.
This approach, however, may present a noticeable service interruption time. Moreover, this approach may provide congestion in the RACH, which can compound the noticeable service interruption time. Furthermore, this approach may lack the capability to provide priority mobility for some use cases, such as, for example, critical communication.
According to a first embodiment, a method can include receiving pre-scheduled uplink grants in a plurality of sub-frames for an incoming user equipment without random access channel. The method can also include receiving a timing advance value or performing timing advance calculation for the incoming user equipment without random access channel. The method can further include sending a plurality of duplicate messages within the plurality of sub-frames based on the received timing advance value or calculated timing advance.
According to a second embodiment, a method can include pre-scheduling uplink grants in a plurality of sub-frames for an incoming user equipment without random access channel. The method can also include performing timing advance calculation for the incoming user equipment without random access channel.
According to a third embodiment, a method can include determining that a user equipment is to be handed over from a source access node to a target access node. The method can also include switching the user equipment to semi-persistent scheduling based on the determination that the user equipment is to be handed over. The method can further include providing information regarding the semi-persistent scheduling to the target access node.
According to fourth through sixth embodiments, an apparatus can include means for performing the method according to the first through third embodiments respectively.
According to seventh through ninth embodiments, an apparatus can include at least one processor and at least one memory and computer program code. The at least one memory and the computer program code can be configured to, with the at least one processor, cause the apparatus at least to perform the method according to the first through third embodiments respectively.
According to tenth through twelfth embodiments, a computer program product may encode instructions for performing a process including the method according to the first through third embodiments respectively.
According to thirteenth through fifteenth embodiments, a non-transitory computer readable medium may encode instructions that, when executed in hardware, perform a process including the method according to the first through third embodiments respectively.
According to sixteenth and seventeenth embodiments, a system may include at least one apparatus according to each of the fourth through sixth embodiments or each of the seventh through ninth embodiments, in communication with one another, for example as shown in
For proper understanding of the invention, reference should be made to the accompanying drawings, wherein:
It may be valuable for communication systems, such as critical communication described in 3GPP technical report (TR) 22.862 to limit the duration of service interruption for mission critical traffic and to support service continuity in a high mobility scenario.
Certain embodiments may provide a mechanism to skip a random access channel (RACH) procedure. The mechanism may help to identify how a target evolved Node B (eNB) can pre-schedule uplink grants for UE without RACH. Also, the mechanism may help to identify how a target eNB can do timing advance (TA) estimation for a UE without RACH.
Certain embodiments, therefore, may have two aspects. According to a first aspect there can be consideration of pre-scheduling uplink grants, and according to the second aspect there can be consideration of timing advance estimation. These aspects may be used separately or together, and certain benefits and/or advantages, as described below, may proceed from the synergies of using both aspects in combination.
According to the first aspect, a target eNB or other access node can pre-schedule consecutive uplink grants in sequential sub-frames for an incoming UE without RACH. The incoming UE can be the UE that is about to be handed over to the target eNB.
The target eNB can decide the time domain for the uplink resources, for example the future sub-frame ‘n+x’ for the UE. Here ‘n’ can refer to the time when target eNB receives an X2-Handover-request message from a source eNB or other access node, and ‘x’ can be the number of sub-frames of delay where the uplink grant will be scheduled for the incoming UE.
The value of ‘T12’, a time to deliver an X2AP message between eNBs, can depend on latency of the Ethernet connection between the eNBs. In a lab test, T12 was about 3 milliseconds. In other implementations, T12 can be determined by eNB's historical data measurements. Thus, T12 may be determined with greater accuracy than simply relying on lab tests.
The sum of the remaining values (T11, T13, T14, T15, and T16) can be obtained from lab or field experiments. For example, the value of a total of 15 milliseconds may be a value based on a lab test result.
This value of ‘x’ may have some variations due to UE performance or eNB load. To deal with this variation, multiple consecutive uplink resources grants can be scheduled for the incoming UE. These may be presented as uplink sub-frame resources from ‘n+x’ to ‘n+x+m’.
According to the second aspect, there may be various methods for a target eNB to do timing advance calculation without RACH. Several options are set forth below, as examples and non-limiting illustrations.
According to a first option, a user equipment can estimate TA based on a downlink (DL) synchronization signal. The UE can be in uplink and downlink sync status in a source cell. Before handover to the target cell, the UE can read a target synchronization signal and calculate downlink time difference between source cell and target cell. The UE can use this difference as an uplink TA value for the target cell.
According to a second option, a user equipment can utilize an observed time difference of arrival (OTDOA).
The UE can measure OTDOA of each neighbor cell and detect a relative time difference between a serving cell and neighbor cells. As demonstrated in
Both the first and second options can rely on calculations that are based on downlink signal estimation. This may, in turn, rely on a hypothesis that downlink and uplink have the same time difference.
According to a third option, the target eNB can measure the incoming UE's uplink data before the UE's handover and can calculate TA for that UE. For example, after making a decision to start handover, the source eNB can changes the UE to semi-persistent scheduling (SPS) and can also include UE's SPS information in the X2-Handover-Request message.
As shown in
At 3, the target eNB can do unlink pre-scheduling for the UE. Based on the UE's SPS information, the target eNB can decode the UE's uplink and calculate timing advance for the UE. The target eNB can schedule the unlink resources in time domain as ‘n+x’ to ‘n+x+m’, where ‘x’ corresponds to UL grant sub-frame delay and ‘m’ corresponds to a number of consecutive sub-frames granted for UE.
At 4, the target eNB can include UL grants and TA in the message X2-Handover-request-response to the source eNB. Then, at 5, the source eNB can forward these UL grants and TA to the UE in the message (rrcConnectionReconfiguration/Handover-command) The UE can then, at 6, apply this TA value and send message(s) within those UL grants to the target eNB without a random access channel procedure.
Thus, in certain embodiments, a source eNB can switch a UE to semi-persistent scheduling when a handover decision is made. The source eNB can include a UE's SPS information in X2-Handover-Request message.
The target eNB can provide pre-scheduling of consecutive uplink grants in sequential sub-frames, and output parameter (n, x, m), having the meanings described above. The target eNB can implement the method of TA calculation based on the third option described above. Thus, the target eNB can include parameters (n, x, m, TA) inside the X2-Handover-Response message. The source eNB can include those parameters (n, x, m, TA) inside message rrcConnectionReconfiguration, The UE can skip any RACH procedure. Moreover the UE can apply the TA and send a first uplink message within those uplink grants.
The uplink grants can be consecutive uplink grants. The plurality of sub-frames can be sequential sub-frames. Examples of these features are illustrated in
The timing advance calculation can include estimating time advance based on a downlink synchronization signal or based on an observed time difference of arrival between signals. For example, the UE can obtain an observed time difference of arrival between signals by comparing the downlink from two neighbor cells, which arrive at different times. These approaches of basing the calculation on a downlink synchronization signal or of basing the calculation on an observed time difference of arrival between signals can correspond to the first and second options described above.
Alternatively, or in addition, the received timing advance can be based on measurements by a target access node of uplink data of the incoming user equipment. In other words, it possible for the UE to calculate TA information itself but also to receive TA information from another node.
The method can further include, at 740, sending a plurality of duplicate messages within the plurality of sub-frames grant while applying same or different timing advance values for each message of the duplicate messages.
The above features of the method may be performed by a user equipment. The following features of the method may be performed by network elements such as a target access node and a source access node.
The method can include, at 750, pre-scheduling uplink grants in a plurality of sub-frames for an incoming user equipment without random access channel The method can also include, at 760, performing timing advance calculation for the incoming user equipment without random access channel The timing advance can be calculated based on measurements by a target access node of uplink data of the incoming user equipment, for example as described above as the third option.
The above access node method features can be performed by a target access node. The following method features can be performed by a source access node. The method can include, at 770, determining that a user equipment is to be handed over from a source access node to a target access node. The method can also include, at 780, switching the user equipment to semi-persistent scheduling based on the determination that the user equipment is to be handed over. The method can further include, at 790, providing information regarding the semi-persistent scheduling to the target access node.
The method can additionally include, at 792, receiving parameters including time advance information of the user equipment from the target access node. The time advance information can include a timing offset or an actual timing advance value. Thus, there may be at least two different implementations. In a first implementation a delta TA can be provided as a timing offset and the UE can do some adjustment calculation, for example +3 or −3, or 2. In a second implementation, an actual TA value can be provided and the UE can apply this TA directly into an uplink message. The method can further include, at 794, providing the parameters to the user equipment.
Each of these devices may include at least one processor or control unit or module, respectively indicated as 814 and 824. At least one memory may be provided in each device, and indicated as 815 and 825, respectively. The memory may include computer program instructions or computer code contained therein, for example for carrying out the embodiments described above. One or more transceiver 816 and 826 may be provided, and each device may also include an antenna, respectively illustrated as 817 and 827. Although only one antenna each is shown, many antennas and multiple antenna elements may be provided to each of the devices. Other configurations of these devices, for example, may be provided. For example, network element 810 and UE 820 may be additionally configured for wired communication, in addition to wireless communication, and in such a case antennas 817 and 827 may illustrate any form of communication hardware, without being limited to merely an antenna.
Transceivers 816 and 826 may each, independently, be a transmitter, a receiver, or both a transmitter and a receiver, or a unit or device that may be configured both for transmission and reception. The transmitter and/or receiver (as far as radio parts are concerned) may also be implemented as a remote radio head which is not located in the device itself, but in a mast, for example. It should also be appreciated that according to the “liquid” or flexible radio concept, the operations and functionalities may be performed in different entities, such as nodes, hosts or servers, in a flexible manner In other words, division of labor may vary case by case. One possible use is to make a network element to deliver local content. One or more functionalities may also be implemented as a virtual application that is provided as software that can run on a server.
A user device or user equipment 820 may be a mobile station (MS) such as a mobile phone or smart phone or multimedia device, a computer, such as a tablet, provided with wireless communication capabilities, personal data or digital assistant (PDA) provided with wireless communication capabilities, portable media player, digital camera, pocket video camera, vehicle, navigation unit provided with wireless communication capabilities or any combinations thereof The user device or user equipment 820 may be a sensor or smart meter, or other device that may usually be configured for a single location.
In an exemplifying embodiment, an apparatus, such as a node or user device, may include means for carrying out embodiments described above in relation to
Processors 814 and 824 may be embodied by any computational or data processing device, such as a central processing unit (CPU), digital signal processor (DSP), application specific integrated circuit (ASIC), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), digitally enhanced circuits, or comparable device or a combination thereof The processors may be implemented as a single controller, or a plurality of controllers or processors. Additionally, the processors may be implemented as a pool of processors in a local configuration, in a cloud configuration, or in a combination thereof
For firmware or software, the implementation may include modules or units of at least one chip set (e.g., procedures, functions, and so on). Memories 815 and 825 may independently be any suitable storage device, such as a non-transitory computer-readable medium. A hard disk drive (HDD), random access memory (RAM), flash memory, or other suitable memory may be used. The memories may be combined on a single integrated circuit as the processor, or may be separate therefrom. Furthermore, the computer program instructions may be stored in the memory and which may be processed by the processors can be any suitable form of computer program code, for example, a compiled or interpreted computer program written in any suitable programming language. The memory or data storage entity is typically internal but may also be external or a combination thereof, such as in the case when additional memory capacity is obtained from a service provider. The memory may be fixed or removable.
The memory and the computer program instructions may be configured, with the processor for the particular device, to cause a hardware apparatus such as network element 810 and/or UE 820, to perform any of the processes described above (see, for example,
Furthermore, although
Certain embodiments may have various benefit and/or advantages. For example, certain embodiments may improve handover performance, for example shortening handover latency, reducing RACH congestion ratio, and providing priority mobility capability for some UEs under scenarios such as critical communication. Thus, for example, this mechanism can be applied to a critical communication scenario when some UE needs extreme high priority mobility support from network.
One having ordinary skill in the art will readily understand that the invention as discussed above may be practiced with steps in a different order, and/or with hardware elements in configurations which are different than those which are disclosed. Therefore, although the invention has been described based upon these preferred embodiments, it would be apparent to those of skill in the art that certain modifications, variations, and alternative constructions would be apparent, while remaining within the spirit and scope of the invention.