Patent Application
20170041848
The invention relates to a method and to a device for data processing in a mobile communication network.
The approach in particular relates to mobile wireless communications, e.g., to 3GPP Long-Term Evolution (LTE as well as LTE-Advanced), in particular to managing load-related aspects of a self-organizing network (SON).
In a handover situation, a mobile terminal (also referred to as user equipment (UE)) is connected from one base station to another (target) base station. The base station may also be referred to as cell, which basically is an area served by the base station. It is noted that a base station, e.g., an eNB, may serve several cells.
When a source cell requests a handover to a target cell, the source cell can indicate a cause for such handover, e.g., “load balancing”.
Negotiating cell-pair specific handover offsets has been discussed in 3GPP. Such handover offsets can be used to obtain stability of load balancing handover (LB-HO) decisions made by a load balancing algorithm, i.e. to prevent handovers back to the overloaded cell. Such a handover back to the overloaded cell is likely to occur, as the mobile terminal (e.g., in active or in idle mode) may not intend to change the cell to which it is currently connected, because from a radio transmission perspective the mobile terminal is served best by this cell. Hence, the mobile terminal will be recognized as a promising HO candidate for radio reasons after having performed a LB-HO to a neighbor cell. This, however, does not lead to an efficient distribution of the overall load among several cells, instead it results in additional traffic based on repeated and futile handovers.
The problem to be solved is to overcome the disadvantages stated above and in particular to define an efficient trigger criterion for modifying a cell-specific handover offset of a base station, in particular of an eNB.
This problem is solved according to the features of the independent claims. Further embodiments result from the depending claims.
In order to overcome this problem, a method is suggested for data processing in a mobile communication network, wherein a handover parameter of at least one cell is negotiated between a first cell and a second cell based on a load situation at the first cell and/or at the second cell.
It is noted that cell in particular refers to an area that is served by a base station. The first cell and the second cell may be served by different base stations, e.g., by different eNBs. A cell performing an action is defined as the base station serving this cell performing said action. However, the base station may provide several (different) actions for different cells associated with this base station.
The handover parameter of each cell may comprise a field of values. In addition, also several handover parameters may be negotiated (and set) between the first cell and the second cell.
It is further noted that the handover parameter of at least one cell being negotiated between said first cell and said second cell can be set for either the first cell or the second cell or both.
Hence, the approach suggested allows for a trigger initiating a negotiation of the parameters to be modified. Such trigger may be defined in an efficient manner to ensure the stability of the load balancing.
Advantageously, the load balancing suggested allows for a joint adjustment of handover parameters, (e.g., handover-offset parameters), which can be defined per cell, in particular per cell pair. Thus, one or two network elements, in particular base stations (Nodes, eNBs) may adapt according to such parameters.
A part of the load balancing functionality may be located and/or associated decentralized in the base stations (e.g., eNBs), wherein a basic configuration and management functionality can be performed by or associated with a central SON entity, which may be deployed with a management plane.
The approach suggested may be applicable in a decentralized manner, i.e. the involved base stations may directly negotiate offset value(s). This bears the advantage that the decentralized negotiation requires less signaling and coordination effort than a centralized negotiation, because in case of the cell-pair specific offset parameters just two base stations get involved. Another advantage is based on the fact that time constraints can be more easily met by the decentralized approach. However, the centralized approach is also applicable and can be used to apply the concepts suggested herein. Also, a mixture of centralized and decentralized approach can be provided (referred to also as hybrid approach).
The base stations (e.g., eNBs) have a more detailed and a more up-to-date knowledge concerning, e.g., the load status of the own cells as well as the load status of cells associated with neighboring base stations due to a X2 resource status reporting.
This approach is applicable for FDD and/or TDD technologies and can be applied to all kind of mobile networks, e.g., GSM, 3G, LTE.
In an embodiment, the handover parameter comprises at least one handover offset, in particular a handover offset value for each of the first cell and the second cell, wherein the handover offset values correspond to one another.
The corresponding handover offset values for paired cells (here: the first cell and the second cell) ensure that the area between the cells is being served without any significant supply gap. Hence, if the first cell reduces its size, the second cell increases its size accordingly by corresponding handover offset values. The same applies vice versa.
In another embodiment, based on the handover parameter negotiation, handover for at least one mobile terminal from the first cell to the second cell is initiated.
Hence, the first cell may efficiently utilize the load situation at the second cell to proceed with or initiate handover of at least one mobile terminal. Advantageously, such handover may relate to several mobile terminals.
In a further embodiment, the load situation of the second cell is conveyed to the first cell and/or the load situation of the first cell is conveyed to the second cell.
The load situation may be conveyed directly from one cell to another or via a central entity.
In a next embodiment, the load situation is conveyed via a status report comprising in particular at least one of the following:
Said status report is also referred to as load report conveying the load situation of, e.g., the potential target cell. The status report may be compressed to at least one field or number indicating the actual effective load that can efficiently be utilized by the source cell.
The status report can be conveyed in a periodic manner and/or it may be event-triggered, e.g., on request or in case a predetermined condition is met.
It is also an embodiment that the handover parameter of the at least one cell is negotiated after at least one load balancing handover has been conducted.
This is also referred to as “trailing” negotiation. The reason for the handover can be indicated by a cause value. The cause value can be conveyed from the source cell to the target cell. The target cell may reject a handover for LB reasons, but still allow handover due to radio reasons.
In particular, a timer can be utilized starting with the first handover of a mobile terminal and considering further handovers that have been conducted within the interval of this timer. These handovers are utilized to negotiate or determine the handover parameter by the first cell (source cell, in particular the base station operating the first cell). This bears the advantage that the negotiation can rely on LB-HOs that have already been performed and is thus rather accurate.
Pursuant to another embodiment, the handover parameter of the at least one cell is negotiated before at least one load balancing handover is conducted.
This approach has the advantage that a LB-HO is only conducted if the cells agree on the changed handover parameter, in particular handover offset.
According to an embodiment, the handover parameter of the at least one cell is negotiated before at least one load balancing handover is conducted; and the handover parameter of the at least one cell is conducted for several mobile terminals.
This approach bears the advantage that in case of a load change, the load balancing function may shift several mobile terminals to a target cell thereby significantly reducing the signaling load required for negotiating the handover parameter.
According to another embodiment, the handover parameter of the at least one cell is negotiated for mobile terminals being in active and/or being in idle mode.
It may be advantageous to be able to select whether the negotiation shall affect mobile terminals in active mode or in idle mode only.
In yet another embodiment, the handover parameter of the at least one cell is negotiated comprising the steps:
It is noted that the different handover parameter suggested may be smaller than the handover parameter provided by the first cell. This allows that the handover parameter negotiated between the first cell and the second cell converges. This scenario in particular applies in case the handover parameter is or comprises a handover offset. Basically, the different handover parameter setting may comprise a parameter that is subject to particular rules or conditions that allow for a converging negotiation.
The first cell may suggest a different handover parameter setting upon receiving either the different handover parameter setting or a rejection of the handover parameter setting suggested. Both, the first cell and the second cell may confirm a handover parameter setting, which may indicate a successful negotiation. The handover parameter agreed on may be utilized for configuration purposes in the first cell as well as in the second cell.
According to a next embodiment, the handover parameter of the at least one cell is negotiated between the first cell and the second cell via a central entity.
Hence, a direct message exchange for negotiation purposes between adjacent cells is not required. Instead, a centralized load balancing function may retrieve information from both cells and provide for the negotiation regarding the handover parameter. The centralized function could be located in or be associated with any Element Manager, OAM node or an independent network element dedicated to provide SON functionality.
Pursuant to yet an embodiment, at least one centralized service is provided by an OAM function.
According to a further embodiment, load balancing is switched off for at least one cell via said OAM function.
Hence, the cell excluded from load balancing is not able to request LB or to initiate LB-HOs. It may also be excluded from suggesting handover parameters to other cells.
According to yet an embodiment, the OAM function provides an upper threshold for load balancing for at least one cell and/or a lower threshold for load balancing for at least one cell.
When the lower threshold is reached, the cell may be switched off for energy saving reasons. The upper threshold can be used to initiate load balancing. Different—in particular separate—thresholds can be utilized for different resource types, e.g., transport network load, hardware load, radio load, and/or for different bearer types, e.g., signaling radio bearers, GBR bearers, non-GBR bearers.
The problem stated above is also solved by a device comprising a and/or being associated with a processor unit and/or a hard-wired circuit and/or a logic device that is arranged such that the method as described herein is executable thereon.
Said device may be a or may be associated with a network component, in particular a base station or a central network element, e.g., a OAM system.
The problem stated supra is further solved by a communication system comprising the device as described herein.
Embodiments of the invention are shown and illustrated in the following figures:
The approach provided herein in particular determines an efficient or advantageous trigger criterion for initiating a negotiation for new cell-pair specific handover offset(s).
This can be used for load balancing purposes, in particular as a functionality of a self-organizing network (SON).
The trigger may be also referred to as any kind of activation and may be timely coupled with a handover, said handover being in particular causal to an action of load balancing (LB), e.g., an action initiated by a load balancing algorithm. For example, said negotiation can be triggered when a LB timer expires.
The LB timer may have to be set to a duration being smaller than a duration of a hysteresis timer that is used for load balancing handover (LB-HO) purposes. Such hysteresis timer may ensure that a mobile terminal just handed over to a target cell stays at least for a particular duration set by the hysteresis timer with the target cell. The LB timer may be started when the first LB-HO is processed.
It is noted that the target cell may refer in particular to a cell associated with a target eNB, whereas a source cell is associated with a source eNB. Hence, although each eNB may comprise several cells, the source cell and the target cell are served by different eNBs.
The mobile terminal mentioned herein refers to any device capable of data communication over a radio interface, in particular a mobile phone, a user equipment (UE), a laptop, a personal digital assistant or any other machine.
The trigger can be used in centralized, in decentralized or in hybrid applications of the load balancing function. In the hybrid scenario, the LB function can be deployed partly in a centralized and partly in a decentralized manner.
The approach described herein utilizes a cell-pair specific offset for active mode UEs according to existing cell-pair specific handover offsets that are used for
Here, the trigger criteria associated with the offset negotiation are described in further detail. The following options relating to the time when a new handover offset is negotiated may be applicable:
According to idle mode and active mode measurement trigger, it may be advantageous to adjust cell-pair specific HO offsets for the active mode.
This cell-pair specific HO offset for the active mode may be used for HO purposes. It is noted that a cell may be free to initiate a HO of a UE to a neighbor cell at any time due to any reason. However, for successful and stable LB purposes, the target cell shall not initiate a HO back to the overloaded source cell immediately after the UE has been handed over, because of the better radio conditions the UE experiences in the source cell.
Hence, cell-pair specific HO offsets may be agreed on between two adjacent cells. By default this HO offset may be set to 0 dB, i.e. a UE may be served by the strongest cell in its vicinity (except for the fact that another HO parameter that defines a HO hysteresis may have an impact on which cell serves the UE).
For performing an LB-HO, the cell-pair specific HO offset of the two cells involved may be modified to avoid any prompt and undesired “Handover Desirable for Radio Reasons” back to the overloaded cell. In principle, this HO offset for active UEs can be combined to either offsets for event triggering of measurement reports for active mode UEs or with offsets which have impact on the camping decision of idle mode UEs.
The HO offset may be dynamically modified by the load balancing function. The term HO offset may also comprise a set of HO offsets that is, e.g., negotiated.
In case an overloaded cell A proposes a new offset value ΔA,Bnew to a target cell B with a current offset value of ΔA,Bcurrent, the target cell B processes this request and provides a response value
ΔA,Bcurrent≦ΔA,Brespond≦A,Bnew.
The values Δ may be similar to the values Qoffset for idle mode and event triggering.
By sending a CELL PAIR COORDINATION REQUEST message, the eNB1 informs the eNB2 about an offset value that is planned by the eNB1, e.g., the eNB1 may want to reduce the offset value by −12 dB. The eNB2 checks whether such request can be fulfilled and in the affirmative, the eNB2 informs the eNB1 about its amended parameter setting by sending a CELL PAIR COORDINATION RESPONSE message, which may comprise the same value with a reverse sign, i.e., +12 dB according to this example. Otherwise, the eNB2 responds with a CELL PAIR COORDINATION REJECT message.
It is noted that in case of trailing negotiation applied by eNB1, the eNB2 may have no reason to reject eNB1's request, because the request means just adapting the cell border to the actual situation that has been changed due to the LB-HO already conducted. Thus, when the eNB1 sends the request, the eNB1 already knows where the new cell border should be set to, because this would correlate to the already successfully performed LB handovers.
The process of negotiation may be initiated per cell-pair specific parameter negotiation. Only one negotiation per cell may be allowed at any point in time. As the procedure can be utilized by other SON functions, it could be advantageous to indicate the purpose of the negotiation in the request, e.g., comprising a “Load Balancing” flag or an indication in the message conveyed.
If the delta value that is requested by eNB1 is too high, the eNB2 may return a smaller value in a CELL PAIR COORDINATION RESPONSE message. This smaller value can be used by the eNB1 as a value mutually agreed upon.
Furthermore, the negotiation may be improved such that a request from one cell may be answered by one of the following:
The coordination comprising the negotiation is terminated by either an accept message or a reject message by the eNB that has received the most recent request, which is indicated by using double arrows in
Hence, the negotiation process between the adjacent eNBs is not required, because the centralized load balancing function has control over both eNB1 and eNB2. Both eNBs may receive new settings for their cell-pair specific offset values. The centralized function could be located in or be associated with any Element Manager, OAM node or an independent network element dedicated to provide SON functionality.
In order to apply operator policies and enable configuration, performance, and fault management, also part of the overall management may advantageously be associated with OAM functionality and/or deployed with an OAM entity.
A central control entity or a function thereof is also referred to as “Operation and Maintenance” (OAM).
It is suggested enabling central control and configuration of a distributed load balancing functionality in particular according to at least one of the following concepts:
The handovers that cause load balancing, an associated X2 load signaling and the HO offset negotiation between a pair of cells can be performed by the decentralized portion of the LB functionality deployed with the NEs 509, 510 (which may in particular be realized as eNBs). An associated signaling between the NEs 509, 510 is provided by the X2 interface.
A particular advantage of this approach is that an overhead, delay and required processing power can be significantly reduced as functionalities being distributed among the network nodes according to the information available. As a further advantage, legacy equipment can be used and/or upgraded in a cost efficient manner.
The approach furthermore provides a flexible framework which can be configured from a centralized setting, e.g., by
It is noted that when conducting a comparison with the lower threshold typically only the user traffic is of interest and therefore the radio load of the network could be used. In case the eNB provides additional services other than supporting and carries its own radio load via its transport link, the transport load could be considered in an assessment whether or not the lower threshold is reached.
Load balancing mechanisms can be in particular effective when load information is being exchanged.
A cell (of a eNB) may at least inform its neighboring cells (of another eNB) to what extent it could accommodate UEs which currently are connected to a congested cell. Advantageously, such information may be as precise as possible. In turn, the congested cell can derive from this information an appropriate action, such as handovers towards the uncongested cell, negotiations of new cell boundaries, etc. Based on an accurate assessment of the congestion level of a potential target cell, the congested cell may choose an appropriate setting, e.g., for HO offset values.
The ability of accommodating load from congested neighbors can be limited according to the following aspects:
Load information is required for a congested cell to direct HO requests to cells which can cope with the additional load. Without such information, a congested cell may blindly launch HO requests towards its neighborhood, which may or may not be successful thereby leading to additional traffic with a high risk of failure and/or a high risk of bouncing back leading to useless repetitions of HO requests.
On the other hand, if the congested cell is well aware of the load situation of the target cell, the following advantages apply:
Hence, a load information of the target cell can be utilized for efficient load balancing.
Conveying the load information leads to additional signaling traffic. However, this overhead traffic can be minimized by informing the neighboring cells about the load situation in an efficient way.
It is noted that the reporting cell may have a preferred knowledge of its own QoS requirements. Advantageously, QoS may be considered in the cell's load report. Hence, the receiving entity of the load report may take into account this information as well rather than assessing or interpreting other data received to obtain a QoS requirement of the target cell, if possible at all. Accordingly, other kind of limitations may also be provided with the load report.
Preferably, the cell receiving the load report may be informed about limitations in total rather than in the individual components. In other words, the cell receiving the load report may advantageously be informed about the amount of traffic that can be handed over to the reporting cell.
It is hence suggested that the reporting cell—rather than signaling each and every component—generates an “effective load” report which contains exactly the information that the receiving cell needs to know, considering any kind of limitation which may apply.
The limitations (e.g., PRB usage) may be separated from their respective causes (hardware load, transport network layer (TNL) load, radio network load) and only the limitations may be conveyed in the load report. This allows the reporting cell to signal any kind of cause, in particular vendor-specific causes in addition to standardized causes. The receiving entity may only care about the limitations, not the respective causes.
The load report may comprise a single field or number compressing the information available at the reporting cell into an efficient format. However, also a lot of different types of information can be compressed this way in an efficient manner to reduce the overall signaling overhead regarding the load report. In particular, several pieces of information can be mapped to a single number indicating the actual traffic condition of the potential target cell. Such mapped information can be directly used by the source cell for load balancing purposes.
In addition or as an alternative, the following information may be conveyed with the load report:
Either one of the information conveyed in the load report may be expressed in relative terms (e.g., in %).
Existing signaling formats, e.g., plain PRB usage, could be used, and the interpretation could be changed at the receiving cell.
Advantageously, the cell receiving the load report is aware of the format and knows how to interpret, e.g., a field or number provided with the load report. In case a format known to other cells is used, each cell receiving a load report is aware of the fact the other neighbors may be aware of and may utilize the resources of the reporting cell as well. Alternatively, the reporting cell may split its available load among its neighbors, and provide load reports accordingly, i.e. the reporting cell may signal an individual report to each neighbor. In this case the receiving cell may assume that the signaled resource can be exclusively utilized.
It may be further specified, when load reports are (to be) sent. At least one of the following options may apply:
It could be advantageous to express the load limitations in several units, e.g.
It is noted that herein “cells” are referred to as exchanging load information. The cell may be associated with a network element, e.g., a base station or a NodeB (eNB) that may actually convey the information to another network element.
In LTE, an eNB may serve several cells and it may collect load information from all of its served cells (also referred to as sectors). The eNB may send this load information to eNBs, which serve a neighbor cell to at least one of its served cells. In other words, load information may not be exchanged between the cells, but between their serving eNBs so that cells receive load information not only from their direct neighbors.
In particular, the following advantages apply:
| Number | Date | Country | |
|---|---|---|---|
| Parent | 13257135 | Sep 2011 | US |
| Child | 15283792 | US |
