Patent Application
20150065137
The present invention has its application within the field of wireless telecommunications and, more particularly, relates to a method and network entities for the determination of criteria used in inter-frequency and inter-system handover in third generation (3G) and beyond 3G (Long Term Evolution: LTE) cellular networks.
The demand for mobile Internet increases every day and, in order to keep up with user preferences, nowadays mobile internet applications are provided by 3G networks, based on Universal Mobile Telecommunications System (UMTS)/High-Speed Packet Access (HSPA) technologies, and, improving third generation, Long Term Evolution (LTE) or LTE Advanced are also deployed. Examples of applications that are used by mobile users are video conferencing, email, messaging and live TV. For most of these applications, mobile users desire that their connections are maintained as their devices move from one access point to another. To provide this service, handover mechanisms are used between access points.
UMTS uses the Universal Terrestrial Radio Access Network (UTRAN) for handovers. The main component in UTRAN is the Radio Network Controller (RNC) which is connected to several base stations called Node B's.
LTE uses Evolved UMTS Terrestrial Radio Access network (EUTRAN) for handovers, which is the evolvement of UTRAN with a functional split between the radio access and core network in the network architecture. Due to this split all radio functionality is placed in the base station network entity, also called eNodeB (an evolved UTRAN Node B). Due to the use of eNodeB with RNC capabilities there is no need for a separate RNC.
Inter Frequency handovers (IFHO) are handovers between different frequencies in the same network. These handovers are used to provide a higher capacity on the cell. Within 3G networks, the RNC triggers the User Equipment (UE) to start measuring and identify cells and, based on the reported measurements, the RNC sends the command to connect to the cell with the lowest load or best signal. The UMTS standard based inter-frequency handover algorithm implements an inter-frequency handover as a hard handover between the different frequency bands [See 3GPP TS 25.331 Radio Resource Control (RRC), Protocol Specification (Release 6); 3GPP TR 25.931 UTRAN Functions]. In LTE, inter-frequency handovers are also possible, e.g. between LTE 2600 MHz and LTE 1800 MHz. And also another kind of inter-frequency handover is occurring between 3G and LTE, changing not only the frequency but also the Radio Access Technology (RAT), these are typically named Inter System Handover (ISHO).
In 3G and LTE there are several frequencies used currently. The spectrum typically used for 3G-UMTS is 2100 MHz in most countries and 900 MHz in countries that have allocated part of this band to GSM and part to UMTS. Every frequency in 3G has a fix of 5 MHz, so there can be up to 5 or 6 carriers used in 3G (e.g., 4 carriers in 2100 MHz-20 MHz—and 2 carriers in 900 MHz-10 MHz). Then, it is quite necessary to do inter-frequency load balancing.
The spectrums typically used in LTE Networks are the 2600 and 800 MHz (aka UHF) bands. In some LTE networks it is possible to use the 1800 MHz band which was used originally by the GSM system (known as DCS). In the case of LTE, every band is a single frequency because of the nature of the LTE OFDMA technology that allows having flexible frequency bandwidth (1.4, 3, 5, 10, 15, 20 MHz). Therefore, in Europe it is possible to have up to 3 frequencies in LTE, and again it is necessary to have a good and efficient inter-frequency handover. And moreover, LTE and 3G are used in the same areas, with the necessity of having good inter-RAT load balancing mechanisms.
Load balancing (or load sharing) algorithms are used to obtain the highest capacity of the system and maximise the use of the radio spectrum, which is one of the most expensive assets of the mobile network operators. Load balancing can be achieved steering the traffic to specific carrier at call set-up or during the call, in order to achieve a target efficient load distribution across several carriers in Packet Switching (PS) calls. As far as the traffic steering during the PS call is concerned, a typical solution is to analyse the load on an amount of carriers and order an IFHO to a number of UEs in order to bring the load of the source and target carriers to a specific value.
The typical load balancing algorithms can be classified in two groups:
The current rise of smartphone utilization is making such load balancing strategies much less effective than they were in the past. Most of PS calls done through smartphones have a short duration and a limited number of packets downloaded. Therefore, the load effect created by handing over to another carrier used by a UE which is a smartphone simply disappears as soon as the PS session finalizes. Besides, moving an ongoing PS (data) session to another carrier has a cost in RNC/eNodeB processing because of the need to enter in compressed mode state and, in addition, sending messages from the RNC/NodeB/eNodeB to the UE for IFHO increases the signalling load of the radio interface.
There are existing systems that describes alternative load balancing approached for IFHO in 3G. For example, US 2013/100839 A1 discloses a system and method wherein, in response to a cell reselection notice, the network, e.g., E-UTRAN or UTRAN, is enabled to provide a wireless device (e.g., UE) with sufficient data to complete a pending data transfer, instead of performing the immediate cell change. Appropriate allocation of radio resources to the wireless device in the current serving cell and before cell change allows reduced packet data transfer latencies for small data sessions, better load balancing and traffic resourcing between cells, appropriate allocation of uplink resources in the new target cell, and enhanced control over network congestion. US 2013/100839 A1 is focused on solving the problem of transmitting the data stored in the buffer when a cell change is going to be done. Some data are sent in the first cell and then it is done the switching. But this is not solving the criteria to choose the user to be eligible in the load balancing handover. Moreover the ‘sufficient data’ to be transmitted is the data already in the buffer pending to be sent to the UE.
Another example of a mobile communications network which includes a load balancing entity is disclosed in WO 2013/045901. The mobile communications network includes a radio network part having one or more base stations for communicating data to or receiving data from mobile communications terminals (Ues). The radio network part is configured to provide a low bandwidth communications interface formed from a low bandwidth carrier for one or more of the UEs to communicate the data to or to receive the data from the mobile communications network in accordance with a relatively low bandwidth, and to provide a high bandwidth communications interface formed from a high bandwidth carrier for one or more of the UEs to communicate the data to or receive the data from the mobile communications network in accordance with a relatively high bandwidth. The load balancing entity in the mobile communications network is configured to monitor the data communicated by the one or more of the UEs to or from the low bandwidth interface and the data communicated by the one or more of the UEs to or from the high bandwidth interface, and consequent upon first predetermined conditions being satisfied to command one of the UEs which is attached for communication to the high bandwidth interface to detach from the high bandwidth interface and to re-attach to the low bandwidth interface for communicating the data to or receiving the data from the mobile communications network via the low bandwidth network. Accordingly communications resources of the mobile communications network which are allocated for the low bandwidth interface may be used more efficiently. The criteria to do this load balancing algorithms are: UEs entering in idle mode, or in Discontinuous Reception mode (DRX), or an inactivity period has happened to the UE, or the throughput is below a threshold. All of them based on the current activity of the terminals, but not forecasting the new data to be transmitted, so not efficient in the long term.
CN102868631 describes a load sharing method which comprises the following steps: extracting factor fields capable of distinguishing data flow in message headers of classified data flow, acting the factor fields as input factors of a default load sharing algorithm of a network forward equipment port, or acting the factor fields as flow characteristics according to each data flow, selecting input factors of load sharing algorithm capable of evenly distributing each data flow for the factor fields, calculating path of each data flow, and forwarding each data flow according to the paths. This load sharing method achieves expansibility increasing of network forward equipment and achieves load balancing. But this is a pure router IP approach based on IP-GTP and UDP headers, without entering in the type of traffic and the pending data to be transmitted, and nothing to do with the 3G and LTE relevant radio interface where the radio link conditions and available capacity makes more complex the load balancing algorithms.
Therefore, there is still a need for an improved management of data (packet switching) sessions in LTE and 3G to minimize signalling load, particularly with the aim of avoiding unnecessary inter-frequency handovers.
The present invention serves to solve the aforesaid problem by providing an inter-frequency handover load balancing method and system, specifically for PS (i.e., data) sessions, based on an assessment of the size of the data session (in time and/or data quantity), by which the inter-frequency handover only occurs where the size is (or is likely to be) significant. This assessment can be based upon an estimated actual duration/data size or based upon identifying an application associated with the data session (e.g. certain apps may be known to be likely to download/upload large amounts of data, such as YouTube).
The present invention is applied for determining the inter-frequency handovers in PS sessions whose handover is expected to make a difference in the load of the current carrier, i.e. those PS sessions (e.g., Video Streaming or Radio streaming) which consume a relevant amount of resources and/or that are expected to last for a relevant amount of time after the handover takes place. On the contrary, PS sessions such as data sessions only involving Instant Messaging are discarded as proper application of the invention.
The present invention is applied for determining inter-frequency handovers as well as inter-system handovers, considering an inter-system handover as a special case of Inter-frequency handover, since Inter-frequency handover occurs while the UE moves among cells but the operating frequency changes and Inter-system handover also occurs when the UE moves among cells with two different operating frequency bands belonging respectively to two different radio access technologies.
The present invention is applicable to all 3G calls (UMTS, HSPA, HSPA+ . . . ) and 4G calls (LTE, LTE Advanced).
An aspect of the invention refers to a method for determining whether to perform an inter-frequency handover (including inter-frequency and inter-system handover) in a telecommunications network, wherein at least a data session of a user equipment (UE) engaged in a call is active and a need of initiating an inter-frequency handover is detected, which comprises the steps of:
In the context of the invention, data sessions are PS sessions and the possible States of data sessions are:
In a particular embodiment, the determination of whether or not to perform inter-frequency handover may be based upon the association of the application with the data session, because in the case that this application is known to typically transmit/receive substantial amounts of data during a data session (e.g. audio/video streaming apps), the remaining time to transmit/receive the data is calculated and the IFHO is performed while this time is not under a minimum.
In another possible embodiment, the determination of whether or not to perform inter-frequency handover may involve a previous estimation of the size of the remaining data to be transmitted/received to get an estimation of the remaining time to transmit/receive the data.
Another aspect of the invention deals with a (3G or beyond 3G) network entity for determining whether to perform an IFHO, e.g. either a RNC either Node-B in UMTS network or a e-NodeB in LTE network, which comprises processing means for performing the method described before. And another aspect of the invention deals with a system for determining whether to perform an IFHO in a (3G or beyond 3G) network which comprises at least one network entity performing the method described before.
A further aspect of the invention refers to a computer program product which comprises program code means to be loaded into processing means of a (3G or beyond 3G) network node in order to execute the described method.
The method and system in accordance with the above described aspects of the invention have a number of advantages with respect to prior art, summarized as follows:
To complete the description that is being made and with the object of assisting in a better understanding of the characteristics of the invention, in accordance with a preferred example of practical embodiment thereof, accompanying said description as an integral part thereof, is a set of drawings wherein, by way of illustration and not restrictively, the following has been represented:
A preferred embodiment of the invention is focused on a method for determining whether to perform an inter-frequency handover or not in 3G and beyond 3G networks.
Then, the RNC/eNodeB computes or evaluates 104 the Remaining Time to Transmit (RemTT) for all the packets of the determined Application Group which are to be transmitted through the open PS session. Depending on the Application Group, the RemTT can be evaluated in different ways, described below. For each Application using the PS session, the RemTT is the expected remaining time before the data content belonging to the Application is fully downloaded.
Depending on the Inter-Frequency Load Balancing Algorithm used by the 3G/4G system, the inter-frequency handover can be scheduled to be executed either at the beginning of the call, i.e., Inter-Frequency Load Balancing at call setup 105, or during the call 108. Once the current algorithm of inter-frequency load balancing detects the necessity of making an IFHO to one or more users, the RNC/eNodeB selects the UEs which are targets for the Handover 107, 110, according to a set of criteria determined by the Inter-Frequency Load Balancing Algorithm 105, 108, currently used.
If the current algorithm of inter-frequency load balancing is Inter-frequency load balancing at call setup 105, the method introduces a new filter to decide if one PS session has to be transferred, i.e., handed over, to another frequency on top of the typical current algorithms. Therefore, once the current inter-frequency load balancing algorithm decides to perform the handover, this method performs a check on the remaining time to transmit RemTT, comparing 106 the evaluated RemTT with a threshold X, configurable by the mobile network operator. The threshold X can define a Minimum RemTT at call Set-Up, expressed in seconds, and hence, the PS session is maintained in the current frequency only if the evaluated RemTT is lower than this threshold X.
In the case that the Inter-frequency load balancing handover is to be executed during the call 108, the method provides criteria for selecting the UEs to be handed-over 109 as follows:
The eligible UEs are those in which the RemTT is higher than a threshold defined as the Minimum RemTT in load balancing handover during the call. Thus, the rest of the UEs have a very low traffic and short time RemTT and, therefore, for those UEs which do not belong to the group of Eligible UEs the handover to another frequency would be useless because there is a risk of call drop and low load balancing effect with those (non-elegible) UEs.
The DL traffic of each Eligible UE is evaluated and several criteria can be used to select one or more UEs:
The UL traffic of each Eligible UE is evaluated and, in addition, information on the produced Uplink interference is obtained for evaluation. In this case, any of the following criteria can be used to select one or more UEs:
Any of the aforementioned and described criteria for Downlink or Uplink overload can be selected.
In
The specific calculation is different per Application Group:
Note that in this text, the term “comprises” and its derivations (such as “comprising”, etc.) should not be understood in an excluding sense, that is, these terms should not be interpreted as excluding the possibility that what is described and defined may include further elements, steps, etc.
| Number | Date | Country | Kind |
|---|---|---|---|
| P201331290 | Aug 2013 | ES | national |
