Patent Application
20130084842
The invention relates generally to mobile communication networks. More particularly, the invention relates to mobility management of user equipment upon changing to a different radio access technology (RAT).
User equipment (UE) may locate in the coverage areas of two different RATs or move to a coverage area of another RAT. When the UE determines, for example, that the currently serving RAT is not providing as good radio coverage as the second RAT would, the UE may perform a cell reselection to the second RAT or the network may trigger a handover of the UE to the second RAT. However, the second RAT and the UE may not be able co-operate optimally at the start due to various reasons.
Embodiments of the invention seek to improve mobility management in the network upon RAT change.
According to an aspect of the invention, there is provided a method as specified in claim 1.
According to an aspect of the invention, there is provided an apparatus as specified in claim 9.
According to an aspect of the invention, there is provided a computer program product as specified in claim 17.
According to an aspect of the invention, there is provided an apparatus comprising means configured to perform any of the embodiments as described in the appended claims.
Embodiments of the invention are defined in the dependent claims.
In the following, the invention will be described in greater detail with reference to the embodiments and the accompanying drawings, in which
The following embodiments are exemplary. Although the specification may refer to “an”, “one”, or “some” embodiment(s) in several locations of the text, this does not necessarily mean that each reference is made to the same embodiment(s), or that a particular feature only applies to a single embodiment. Single features of different embodiments may also be combined to provide other embodiments.
Radio communication networks, such as the Long Term Evolution (LTE) or the LTE-Advanced (LTE-A) of the 3rd Generation Partnership Project (3GPP), are typically composed of at least one base station (also called a base transceiver station, a radio network controller, a Node B, or an evolved Node B, for example), at least one user equipment (UE) (also called a user terminal, terminal device or a mobile station, for example) and optional network elements that provide the interconnection towards the core network. The base station connects the UEs via the so-called radio interface to the network. The base station may provide radio coverage to a cell, control radio resource allocation, perform data and control signaling, etc. The cell may be a macrocell, a microcell, or any other type of cell where radio coverage is present.
In general, a base station may be configured to provide communication services according to at least one of the following radio access technologies (RATs): Worldwide Interoperability for Microwave Access (Wi-MAX), Global System for Mobile communications (GSM, 2G), GSM EDGE radio access Network (GERAN), General Packet Radio Service (GRPS), Universal Mobile Telecommunication System (UMTS, 3G) based on basic wideband-code division multiple access (W-CDMA), high-speed packet access (HSPA), LTE, and/or LTE-A. The present embodiments are not, however, limited to these protocols. The base station may be node B (NB) or an evolved node B (eNB) as in the LTE or in the LTE-A, a radio network controller (RNC) as in the UMTS, a base station controller (BSC) as in the GSM/GERAN, or any other apparatus capable of controlling radio communication and managing radio resources within the cell.
Such a scenario where the user equipment is located in coverage areas of several RATs may exist, as is shown in
The reason for the handover may be that the radio coverage from the other RAT is better than from the currently serving RAT, or that the UE 120 needs services that are provided by the other RAT and not the currently serving RAT. On the other hand, when the UE 120 is in an idle mode (such as in an RRC_idle mode in the LTE) or when the UE 120 starts up, the UE 120 may decide to make a cell reselection. The target cell in the reselection may belong to a RAT that is different from the earlier RAT. Thus, the UE 120 may end up being served by a RAT which is different from the currently serving RAT as opposed to intra-RAT cell changes.
For example, in the UMTS and in the LTE, the UE may keep track of the speed of the UE. The speed may be determined, for example, by detecting the number of cell changes in a certain time window (such as t-evaluation), the speed may be obtained from the network, or it may be obtained from the global position in system (GPS), for example. The speed of the UE may then determine a mobility state of the UE, i.e. depending on the detected number of cell changes in the defined time window, for example, the UE changes its mobility state. The mobility state may be represented with one of a plurality of values, such as normal, medium and high, for example. Alternatively, the mobility state may be represented by a numerical value, for example. The mobility state may affect how the UE behaves. In an embodiment, once the UE determines that criteria for another mobility state is reached, certain parameters (depending on whether the UE is in the RRC_IDLE or in the RRC_CONNECTED) are scaled accordingly. For example, the UE may (if so commanded by the network), after detecting a high mobility state (for example, the UE is moving in high speed), adjust the measurement reporting—related parameters to trigger measurement report to the network with shorter triggering times as well as scale the associated signal quality thresholds (as commanded by the network), for example. This in turn may trigger the network to command a handover more rapidly than if the UE was in normal or medium mobility state. Naturally, there may be more parameters to adjust than the handover triggering, as known by a skilled person.
The UE may obtain the criteria for changing into different mobility states from the RAT as part of initial broadcast information when the UE moves to or becomes operational in a new RAT. Alternatively or in addition to, the UE may be precoded with such information. In yet another embodiment, the information may be unicasted to the UE, i.e. by using point-to-point messages, where message(s) is/are dedicated/addressed to one UE only, or multi casted to the UE, i.e. by transmitting, by the network, a message to a group of UEs. There may also be further instructions that the UE may follow when setting its mobility state. For example, when the mobility state is changed on the basis of how many cell changes are made, it may be that the UE may not count consecutive reselections or handovers between same two cells into mobility state detection criteria if same cell is selected just after one other selection.
However, what may happen is that the UE has fulfilled the criteria for certain mobility state (e.g. in a fast train) and therefore has set the mobility state into the high state, for example. Then the UE may change to another RAT (either by being commanded by the network via a handover or a cell change order, or by itself via a cell reselection, as per the standards relevant for each particular radio access technology). Even though the UE may have previously set its state into the high mobility state (or, may have performed an amount of cell reselections or handovers that would qualify the UE to enter the medium or the high mobility state according to the mobility state-related parameters valid in the target cell/radio access technology), the UE starts in the new RAT with normal state even if still moving fast. The same may happen when the UE temporarily visits the new RAT and then returns to the original RAT, i.e., the UE still starts off with normal mobility mode in the original RAT, even if the mobile is still moving fast. However, it may also be that the original RAT keeps the number of cell changes stored in a memory and when the UE returns to the original RAT, the RAT continues calculating the number of cell changes from the stored number onwards. This may depend on the duration of a time window within which the cell changes need to take place. In other words, the RAT may see all the cell changes in the current RAT within the time window even if the UE has visited another RAT in between of the previous cell change and the current point in time. For instance, if the UE has carried out a cell change in the LTE two minutes ago, has after that visited the UMTS RAT and has then entered again to the LTE cell where the time-window is determined as three minutes, the cell change that happened two minutes ago in the LTE may be taken into account. However, it may happen that it may take some time for the UE to set its mobility state into the high mode in the new RAT because the UE is not initially in the correct mobility state. This may cause problems in the selected RAT as the UE is moving in high speed with parameters that are not scaled correctly.
At least partly for this reason, a more optimal solution is needed for inter-RAT scenarios with respect to mobility management. Therefore it is proposed that, as shown in
As said, the UE may obtain information related to its speed in a plurality of means, such as GPS positioning system, from the network, etc. For the sake of simplicity, let us assume that the UE 200 obtains this information by detecting the number of cell changes within a time window.
The mobility state may be determined so that the UE determines the number of cell changes (in this example handovers) within the time window 270A, for example. In general the network may determine that when x cell changes has been performed during the time window 270, the UE changes into the medium mobility state and when y cell changes has been performed during the time window 270, the UE changes into the high mobility state, for example. Also, the UE keeps or changes into the normal mobility state, when the number of cell changes is less than or equal to x, for example. Now it may be seen from
As said, the cell 220 is served by a LTE base station (eNB) whereas the cell 214 is served by the UMTS base station. Thus, the handover from the cell 214 to the cell 220 is an inter-RAT handover. When the UE is in the cell 214, the mobility state is already set as the high mobility state because the handovers have been made with such a high density, as said above. However, in prior art, when the UE changes to the new RAT (in this case to the LTE) by performing the handover 258, the UE would not take any information related to the speed of the UE in the first RAT (for example the previous UMTS RAT) into use in the new LTE RAT. This would directly cause the UE 200 to start from the normal mobility state as the initial mobility state of the UE 200 in the second RAT, i.e. in the cell 220 even though the UE 200 might still be running fast. Assuming that two handovers within the RAT-specific time window 272 need to be made in order to change into the high mobility state also in the LTE, it would take till the point where handover 262 is made before the UE 200 would change its LTE mobility state into the high mobility state. Even worse, in some cases it might take till the end of time window 272 before the UE 200 would change its state, depending on the system configuration.
Now according to the proposed solution, the UE advantageously takes the obtained mobility related information into use when entering a new RAT. In an embodiment this takes place substantially immediately in point when the handover 258 is made. For example, the UE 200 may use the mobility related information which has been obtained in the past (in one or more RATs) to determine the mobility state in the next RAT. In an embodiment, the mobility related information comprises the number of cell reselections, cell change orders and handovers that have taken place in the past (in the one or more RATs). This may provide significant advantage to the UE 200 as it immediately scales the parameters that are scalable depending on the set mobility state correctly.
It should also be noted, that the at least one first RAT comprises in an embodiment the present RAT the UE 200 is communicating with before changing to the second RAT. In the embodiment of
In an embodiment, the UE may detect the number of cell changes within at least a known recording period in at least one RAT. For this it is assumed that the at least one RAT, a first RAT and/or a second RAT, employs a RAT-specific sliding time window, such as the time window 270 or 272, during which the cell changes within the specific RAT are to be detected. In this embodiment, the known recording period may be at least as long as the maximum defined length of the at least one RAT-specific sliding time window. That is, at least as long as the maximum defined value for the t-evaluation parameter among the at least one RAT. Thus, the UE may not store the cell changes with time stamps for perpetuity, but at least for a known recording period. This may allow the UE to save the memory resources, for example.
The UE may be precoded with knowledge of the defined RAT-specific sliding time window maximum lengths. For example, an UE with capabilities to operate in the UMTS and in the LTE may be precoded with LTE and UMTS RAT specifications which may determine the maximum defined valued for the t-evaluation in both of the RATs. Then the UE may select the longer of the values as the known recording period. For example, when the maximum defined value for the time window duration in a RAT R1 is 10 minutes, in RAT R2 it is 15 minutes and in RAT R3 it is 5 minutes, then the UE may keep the records of cell changes for up to 15 minutes, regardless in which RAT it is operating. This may enable the UE to always correctly assess the UE mobility state in any given RAT.
In an embodiment, the information related to the speed of the user equipment comprises a mobility state of the user in the present first radio access technology. This was shown in
In
In another embodiment, the information related to the speed of the user equipment comprises the number of cell changes performed in the at least one first radio access technology, wherein the cell changes comprise at least one of a handover, a cell change order and a cell reselection. This is shown in
In
It should be noted that the criteria for different mobility states may be different between different RATs. Therefore, the mobility state of the first RAT may not correspond to the same mobility state in the second RAT. Thus, a kind of mapping table between the criteria of different RATs may be of use. The UE may, for example, determine that two cell changes in the first RAT (which may indicate high mobility state in the first RAT) may lead to medium mobility state in the second RAT. By having the information related to the cell changes and to the timing of the cell changes stored in the UE or the time duration during which the cell changes have taken place, the UE may use that information in the second RAT together with the criteria of the second RAT. In an embodiment, the UE may inherit the amount or number of cell changes in a maximum amount of evaluation time defined in the specification instead of the actual mobility state. As a result, the UE may apply the mobility state determined in the second RAT as an initial mobility state of the UE in the second RAT. From then on the UE may control the mobility state in the second RAT in step 510, which controlling may take place in a similar manner as shown in
An embodiment, as shown in
The apparatus 600 may comprise the terminal device of a cellular communication system, e.g. a computer (PC), a laptop, a tabloid computer, a cellular phone, a communicator, a smart phone, a palm computer, or any other communication apparatus. In another embodiment, the apparatus is comprised in such a terminal device, e.g. the apparatus may comprise a circuitry, e.g. a chip, a processor, a micro controller, or a combination of such circuitries in the terminal device and cause the terminal device to carry out the above-described functionalities. Further, the apparatus 600 may be or comprise a module (to be attached to the UE) providing connectivity, such as a plug-in unit, an “USB dongle”, or any other kind of unit. The unit may be installed either inside the UE or attached to the UE with a connector or even wirelessly.
As said, the apparatus 600 may comprise the at least one processor 602. The at least one processor 602 may be implemented with a separate digital signal processor provided with suitable software embedded on a computer readable medium, or with a separate logic circuit, such as an application specific integrated circuit (ASIC). The at least one processor 602 may comprise an interface, such as computer port, for providing communication capabilities.
The at least one processor 602 may comprise a mobility management circuitry 608. The circuitry 608 may be responsible of setting the mobility state of the apparatus 600. The circuitry 608 may obtain information of the criteria for the mobility states, for example. The circuitry 608 may perform scaling of certain parameters depending on which mobility state is reached. The circuitry 608 may also detect the number of cell changes performed. Even though not shown, the apparatus 600 may comprise a clock which may be of use when applying a RAT- or cell-specific time window or the known recording period, for example.
The at least one processor 602 may also comprise an inter-RAT management circuitry 610 for managing the scenarios where the serving RAT changes. The circuitry 610 may perform a handover or a cell reselection to the new RAT, updating of certain parameters due to the inter-RAT change, for example.
The apparatus 600 may further comprise radio interface components 606 providing the apparatus with radio communication capabilities with the radio access network. The radio interface components 606 may comprise standard well-known components such as amplifier, filter, frequency-converter, (de)modulator, and encoder/decoder circuitries and one or more antennas.
As said, the apparatus 600 may comprise a memory 604 for storing information. The information stored may comprise for example the criteria for the mobility states, information related to the time windows in different RATs, the mobility state of the apparatus 600, the detected number of cell changes, GPS data, etc.
As used in this application, the term ‘circuitry’ refers to all of the following: (a) hardware-only circuit implementations, such as implementations in only analog and/or digital circuitry, and (b) combinations of circuits and software (and/or firmware), such as (as applicable): (i) a combination of processor(s) or (ii) portions of processor(s)/software including digital signal processor(s), software, and memory(ies) that work together to cause an apparatus to perform various functions, and (c) circuits, such as a microprocessor(s) or a portion of a microprocessor(s), that require software or firmware for operation, even if the software or firmware is not physically present. This definition of ‘circuitry’ applies to all uses of this term in this application. As a further example, as used in this application, the term ‘circuitry’ would also cover an implementation of merely a processor (or multiple processors) or a portion of a processor and its (or their) accompanying software and/or firmware. The term ‘circuitry’ would also cover, for example and if applicable to the particular element, a baseband integrated circuit or applications processor integrated circuit for a mobile phone or a similar integrated circuit in a server, a cellular network device, or another network device.
The techniques and methods described herein may be implemented by various means. For example, these techniques may be implemented in hardware (one or more devices), firmware (one or more devices), software (one or more modules), or combinations thereof. For a hardware implementation, the apparatus(es) of embodiments may be implemented within one or more application-specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), processors, controllers, micro-controllers, microprocessors, other electronic units designed to perform the functions described herein, or a combination thereof. For firmware or software, the implementation can be carried out through modules of at least one chip set (e.g. procedures, functions, and so on) that perform the functions described herein. The software codes may be stored in a memory unit and executed by processors. The memory unit may be implemented within the processor or externally to the processor. In the latter case, it can be communicatively coupled to the processor via various means, as is known in the art. Additionally, the components of the systems described herein may be rearranged and/or complemented by additional components in order to facilitate the achievements of the various aspects, etc., described with regard thereto, and they are not limited to the precise configurations set forth in the given figures, as will be appreciated by one skilled in the art.
Thus, according to an embodiment, the apparatus comprises processing means configure to carry out embodiments of any of the
Embodiments as described may also be carried out in the form of a computer process defined by a computer program. The computer program may be in source code form, object code form, or in some intermediate form, and it may be stored in some sort of carrier, which may be any entity or device capable of carrying the program. For example, the computer program may be stored on a computer program distribution medium readable by a computer or a processor. The computer program medium may be, for example but not limited to, a record medium, computer memory, read-only memory, electrical carrier signal, telecommunications signal, and software distribution package, for example.
Even though the invention has been described above with reference to an example according to the accompanying drawings, it is clear that the invention is not restricted thereto but can be modified in several ways within the scope of the appended claims. Therefore, all words and expressions should be interpreted broadly and they are intended to illustrate, not to restrict, the embodiment. It will be obvious to a person skilled in the art that, as technology advances, the inventive concept can be implemented in various ways. Further, it is clear to a person skilled in the art that the described embodiments may, but are not required to, be combined with other embodiments in various ways.
