WO2013059979A1

WO2013059979A1 - Method and network entity for managing communications according to a first radio access technology and according to a second radio access technology

Info

Publication number: WO2013059979A1
Application number: PCT/CN2011/081186
Authority: WO
Inventors: Malte Schellmann; Markus M. DILLINGER; Soroush GHAMARI
Original assignee: Huawei Technologies Co., Ltd.
Priority date: 2011-10-24
Filing date: 2011-10-24
Publication date: 2013-05-02
Also published as: CN104054365A

Abstract

The invention relates to a method (101) for managing communications according to a first radio access technology (RAT1) and according to a second radio access technology (RAT2), wherein a first dedicated frequency band (DB1) is assigned for communications according to the first radio access technology (RAT1) and a second dedicated frequency band (DB2) is assigned for communications according to the second radio access technology (RAT2). The method comprises that a flexible frequency band (FB) is assigned (102) either for communications according to the first radio access technology (RAT1) or for communications according to the second radio access technology (RAT2).

Description

DESCRIPTION

Method and network entity for managing communications according to a first radio access technology and according to a second radio access technology

BACKGROUND OF THE INVENTION

The present invention relates to a method for managing communications according to a first radio access technology and according to a second radio access technology and a network entity for managing communications according to a first radio access technology and according to a second radio access technology.

For any type of radio system being operated today, frequency spectra are assigned by following a fixed spectrum allocation policy. With respect to radio access technologies (RATs), this means that there is a dedicated frequency band used exclusively by one RAT operated by a single operator. The demand in bandwidth for broadband radio services is expected to grow enormously. At the same time, spectrum available in the frequency bands of interest, which could be used to satisfy this demand is running short.

Hence, there is a demand for improving the performance of cellular radio communication systems with respect to bandwidth allocation.

SUMMARY OF THE INVENTION

It is the object of the invention to provide a concept for increasing the performance of radio communications. This object is achieved by the features of the independent claims. Further implementation forms are apparent from the dependent claims, the description and the figures.

The invention is based on the finding that by flexibly assigning a flexible frequency band either for communications according to a first radio access technology, e.g. LTE, or for communications according to a second radio access technology, e.g. UMTS or HSDPA or GSM, spectrum resources of the two radio access

technologies may be more efficiently used, thereby enabling the radio

communications system to counteract overload situations resulting in a higher system stability.

In order to describe the invention in detail, the following terms, abbreviations and notations will be used:

RAT: Radio Access Technology

DB: Dedicated Frequency Band (dedicated band)

FB: Flexible Frequency Band (flex band)

KPI : Key Performance Indicator

NMS: Network Management System

DSM: Dynamic Spectrum Manager

SR: Spectrum Reallocation

UMTS: Universal Mobile Telecommunications System LTE: Long Term Evolution

HSDPA: High Speed Data Packet Access

GSM: Global System for Mobile Communications

PMSE: Program Making and Special Events

QoS: Quality of Service

CM: Configuration Management

PM: Performance Monitoring

SON: Self-Organizing Network

According to a first aspect, the invention relates to a method for managing communications according to a first radio access technology and according to a second radio access technology, wherein a first dedicated frequency band is assigned for communications according to the first radio access technology and a second dedicated frequency band is assigned for communications according to the second radio access technology, the method comprising: assigning a flexible frequency band either for communications according to the first radio access technology or for communications according to the second radio access technology.

Thus, the flexible frequency band can be used in addition to the respective dedicated frequency band. The method can be performed during an existing communication according to one of the radio access technology in order to dynamically increase a communication bandwidth. The communications according to the first radio access technology and according to the second radio access technology can be managed by the same network operator.

As the first dedicated frequency band is assigned for communications according to the first radio access technology, dedicated frequency band may be considered as being assigned to the first radio access technology. Correspondingly, the second dedicated frequency band can be considered as being assigned to the second radio access technology. Thus, the flexible frequency band can be considered as enhancing the available spectrum for the first radio access technology and/or for the second radio access technology.

In a first possible implementation form of the method according to the first aspect, the method comprises: monitoring, in particular continuously monitoring, a key performance indicator indicating an amount of free resources in the first dedicated frequency band; and assigning the flexible frequency band for communications according to the first radio access technology if the key performance indicator crosses, e.g. exceeds, a predetermined threshold; or monitoring, in particular continuously monitoring, a key performance indicator indicating an amount of free resources in the second dedicated frequency band; and assigning the

predetermined flexible frequency band for communications according to the second radio access technology if the key performance indicator crosses a predetermined threshold.

In a second possible implementation form of the method according to the first implementation form of the first aspect, the key performance indicator is represented by the amount of free resources in the system, and the threshold is determined by the future demand of additional resources.

The calculation of the threshold is based on at least one of: an arrival rate of users entering the system to communicate according to the first radio access technology or to the second radio access technology, an amount of communication resources required for serving a single user communicating according to the first radio access technology or to the second radio access technology.

The calculation of the threshold can be based on at least one of: an arrival rate of users entering the system to communicate according to the first radio access technology or to the second radio access technology, and an amount of communication resources required for serving a single user communicating according to the first radio access technology or to the second radio access technology.

In a third possible implementation form of the method according to the first aspect as such or according to any of the preceding implementation forms of the first aspect, the flexible frequency band is assigned for communications according to the first radio access technology, and the method comprises handing over users communicating in the flexible frequency band according to the first radio access technology to the first dedicated frequency band to free the flexible frequency band if additional communication resources are required for communications according to the second radio access technology, and assigning the flexible frequency band for communications according to the second radio access technology; or wherein the flexible frequency band is assigned for communications according to the second radio access technology, and wherein the method comprises handing over users communicating in the flexible frequency band according to the second radio access technology to the second dedicated frequency band to free the flexible frequency band if additional communication resources are required for communications according to the first radio access technology, and assigning the flexible frequency band for communications according to the first radio access technology.

In a fourth possible implementation form of the method according to the first aspect as such or according to any of the preceding implementation forms of the first aspect, the method further comprises determining a utility function, the utility function indicating a change of a communication load due to an assignment of the flexible frequency band to one of either the first radio access technology or the second radio access technology; and assigning the flexible frequency band either for communications according to the first radio access technology or for communications according to the second radio access technology only if the utility function fulfils a utility criterion.

In a fifth possible implementation form of the method according to the fourth implementation form of the first aspect, the utility criterion is fulfilled if the utility function is equal to or greater than a utility threshold.

In a sixth possible implementation form of the method according to the fourth or the fifth implementation form of the first aspect, the utility function depends on at least one of: a first relative load indicating an amount of consumed resources versus an amount of available resources on the first radio access technology before the assignment of the flexible frequency band to one of either the first radio access technology or the second radio access technology; a second relative load indicating an amount of consumed resources versus an amount of available resources on the second radio access technology before the assignment of the flexible frequency band to one of either the first radio access technology or the second radio access technology; a first predicted relative load indicating a predicted amount of consumed resources versus a predicted amount of available resources on the dedicated frequency band of the first radio access technology after the assignment of the flexible frequency band to one of either the first radio access technology or the second radio access technology; and a second predicted relative load indicating a predicted amount of consumed resources versus a predicted amount of available resources on the dedicated frequency band of the second radio access technology after the assignment of the flexible frequency band to one of either the first radio access technology or the second radio access technology. In a seventh possible implementation form of the method according to the sixth implementation form of the first aspect, the utility function depends on a difference between a sum of the first relative load and the second relative load and a sum of the first predicted relative load and the second predicted relative load.

In an eighth possible implementation form of the method according to any of the fourth to the seventh implementation forms of the first aspect, the method further comprises: determining an amount of free resources in the first dedicated frequency band of the first radio access technology before the assignment of the flexible frequency band to the first radio access technology; and releasing the flexible frequency band from being assigned to the first radio access technology if the amount of free resources in the first dedicated frequency band crosses a first threshold or determining an amount of free resources in the second dedicated frequency band of the second radio access technology before the assignment of the flexible frequency band to the second radio access technology; and releasing the flexible frequency band from being assigned to the second radio access technology if the amount of free resources in the second dedicated frequency band crosses a second threshold.

In a ninth possible implementation form of the method according to the eighth implementation form of the first aspect, the flexible frequency band is released if the amount of free resources in the first dedicated frequency band is equal to or greater than the first threshold or if the amount of free resources in the second dedicated frequency band is equal to or greater than the second threshold.

In a tenth possible implementation form of the method according to the eighth implementation form or according to the ninth implementation form of the first aspect, the first threshold depends on at least one of: a number of users in the flexible frequency band, an arrival rate of users entering the system to

communicate according to the first radio access technology, an amount of communication resources required for serving a single user communicating according to the first radio access technology; and the second threshold depends on at least one of: a number of users in the flexible frequency band, an arrival rate of users entering the system to communicate according to the second radio access technology, an amount of communication resources required for serving a single user communicating according to the second radio access technology.

In an eleventh possible implementation form of the method according to the first aspect as such or according to any of the preceding implementation forms of the first aspect, the method further comprises determining an extended utility function, the extended utility function indicating a change of a communication load including overload due to an assignment of the flexible frequency band to one of either the first radio access technology or the second radio access technology; and assigning the flexible frequency band either for communications according to the first radio access technology or for communications according to the second radio access technology only if the extended utility function fulfils an extended utility criterion.

In a twelfth possible implementation form of the method according to the eleventh implementation form of the first aspect, the extended utility criterion is fulfilled if the extended utility function is equal to or greater than an extended utility threshold.

In a thirteenth possible implementation form of the method according to the eleventh implementation form or according to the twelfth implementation form of the first aspect, the extended utility function depends on at least one of: a first relative load indicating an amount of consumed resources versus an amount of available resources on the first radio access technology before the assignment of the flexible frequency band to one of either the first radio access technology or the second radio access technology; a first overload indicating an overload in the first radio access technology before the assignment of the flexible frequency band to one of either the first radio access technology or the second radio access technology; a second relative load indicating an amount of consumed resources versus an amount of available resources on the second radio access technology before the assignment of the flexible frequency band to one of either the first radio access technology or the second radio access technology; a second overload indicating an overload in the second radio access technology before the

assignment of the flexible frequency band to one of either the first radio access technology or the second radio access technology; a first predicted relative load indicating a predicted amount of consumed resources versus a predicted amount of available resources on the dedicated frequency band of the first radio access technology after the assignment of the flexible frequency band to one of either the first radio access technology or the second radio access technology; a first predicted overload indicating a predicted overload in the first radio access technology after the assignment of the flexible frequency band to one of either the first radio access technology or the second radio access technology; a second predicted relative load indicating a predicted amount of consumed resources versus a predicted amount of available resources on the dedicated frequency band of the second radio access technology after the assignment of the flexible frequency band to one of either the first radio access technology or the second radio access technology; and a second predicted overload indicating a predicted overload in the second radio access technology after the assignment of the flexible frequency band to one of either the first radio access technology or the second radio access technology.

In a fourteenth possible implementation form of the method according to the thirteenth implementation form of the first aspect, the extended utility function depends on a difference between a sum of the first relative load, the first overload, the second relative load and the second overload and a sum of the first predicted relative load, the first predicted overload, the second predicted relative load and the second predicted overload.

In a fifteenth possible implementation form of the method according to the thirteenth implementation form or according to the fourteenth implementation form of the first aspect, the first predicted overload depends on at least one of: an amount of resources in the first dedicated frequency band or in the second dedicated frequency band necessary for serving future users, an amount of free resources in both the first dedicated frequency band and the flexible frequency band or an amount of free resources in both the second dedicated frequency band and the flexible frequency band, and a total amount of resources in the first radio access technology or a total amount of resources in the second radio access technology; and the second predicted overload depends on at least one of: an amount of resources in the first dedicated frequency band or in the second dedicated frequency band necessary for serving future users and in the flexible frequency band necessary for serving current users, an amount of free resources in the first dedicated frequency band or an amount of free resources in the second dedicated frequency band, and a total amount of resources in the first radio access technology or a total amount of resources in the second radio access technology.

In a sixteenth possible implementation form of the method according to the fifteenth implementation form of the first aspect, the first predicted overload depends on a difference of the amount of resources in the first dedicated frequency band necessary for serving future users and the amount of free resources in both the first dedicated frequency band and the flexible frequency band, the difference being normalized by the total amount of resources in the first radio access technology, or the first predicted overload depends on a difference of the amount of resources in the second dedicated frequency band necessary for serving future users and the amount of free resources in both the second dedicated frequency band and the flexible frequency band, the difference being normalized by the total amount of resources in the second radio access

technology; and the second predicted overload depends on a difference of an amount of resources in the first dedicated frequency band necessary for serving future users and in the flexible frequency band necessary for serving current users and an amount of free resources in the first dedicated frequency band, the difference being normalized by the total amount of resources in the first radio access technology, or the second predicted overload depends on a difference of an amount of resources in the second dedicated frequency band necessary for serving future users and in the flexible frequency band necessary for serving current users and an amount of free resources in the second dedicated frequency band, the difference being normalized by the total amount of resources in the second radio access technology.

In a seventeenth possible implementation form of the method according to the first aspect as such or according to any of the preceding implementation forms of the first aspect, the first radio access technology comprises a UMTS technology and the second radio access technology comprises an LTE technology or the first radio access technology comprises an LTE technology and the second radio access technology comprises a UMTS technology.

In an eighteenth possible implementation form of the method according to the first aspect as such or according to any of the preceding implementation forms of the first aspect, each of the first dedicated frequency band, the second dedicated frequency band and the flexible frequency band comprises a 5 MHz spectrum band.

In a nineteenth possible implementation form of the method according to the first aspect as such or according to any of the preceding implementation forms of the first aspect, the assigning is performed automatically, i.e. by a processor.

In a twentieth possible implementation form of the method according to the first aspect as such or according to any of the preceding implementation forms of the first aspect, assigning is performed dynamically, e.g. during an existing

communication according to one of the radio access technologies. Thereby, the available communication spectrum can be dynamically increased if e.g. an increased payload is expected. According to a second aspect, the invention relates to a network entity for managing communications according to a first radio access technology and according to a second radio access technology and a first dedicated frequency band is assigned to the first radio access technology, wherein a second dedicated frequency band is assigned to the second radio access technology, the network entity comprising: a coordination processor for processing an assignment of a flexible frequency band either for communications according to the first radio access technology or for communications according to the second radio access technology.

In a first possible implementation form of the network entity according to the second aspect, the coordination processor is configured to perform a method according to the first aspect as such or according to any of the implementation forms of the first aspect.

In a second possible implementation form of the network entity according to the second aspect as such or according to the first implementation form of the second aspect, the network entity further comprises a coordination interface coupleable to a network management system, the network management system being configurable to receive the assignment processed by the coordination processor and to assign the flexible frequency band according to the assignment processed by the coordination processor.

In a third possible implementation form of the network entity according to the second implementation form of the second aspect, the coordination interface is configured to transmit a key performance indicator indicating an amount of free resources in the first dedicated frequency band or an amount of free resources in the second dedicated frequency band to the coordination processor. According to a third aspect, the invention relates to a computer program for implementing a method according to the first aspect as such or according to any of the implementation forms of the first aspect.

Aspects of the invention provide an effective solution to solve overload situations in case of asymmetric load in RATs. The solution can be implemented as an autonomous Self-Organizing Network (SON) functionality, which is processed individually per sector cell. Cost evaluation based on utility function prevents spectrum reallocation in case of a balanced load situation. The Ping-pong effect, i.e. the flex band is alternately assigned to different RATs, can reliably be avoided. The solution is multi-vendor applicable, as the north interface is involved for the network management system (NMS).

When using a method according to the first aspect, manual network planning can be avoided by using automatic processing as provided by the method according to the first aspect. Reallocation of spectrum form one RAT to another, termed

"spectrum refarming", e.g. refarming of GSM and UMTS frequencies to LTE, can be performed independently from ownership of the RATs. Manual network planning can be replaced by the automated spectrum refarming method according to the first aspect of the invention. Automated refarming according to aspects of the invention falls in the category of Self-planning for self-organizing networks (SON). By using the method according to the first aspect, system degradations during RAT refarming are avoided or at least minimized.

By implementing a dynamic spectrum access policy for RATs according to aspects of the invention, spectrum is not exclusively used by a single radio service and thus an inefficient use of the spectrum is avoided, even when the load conditions for different radio systems differ substantially. In particular, the handicap that spectrum of one system is crowded due to a high number of service requests in a hot spot scenario, while the spectrum of another system is only scarcely used, is overcome. If one radio system is allowed to„borrow" unused frequency resources from another system, according to aspects of the invention, the problem of spectrum shortage is relaxed while the efficiency of spectrum use is optimized. Methods according to the first aspect of the invention may also be summarized under the term„spectrum sharing".

According to aspects of the invention spectrum for mobile radio systems may be shared between different operators using not only the same but different RATs. The spectrum borrowed to the another operator does not necessarily need to be freed, allowing for a flexible inter-operator resource management of high granularity.

Aspects of the invention may be applied for spectrum sharing between

heterogeneous radio services, in particular in the context of utilizing White Spaces in the TV broadcast frequency spectrum. Techniques for global spectrum management according to aspects of the invention enable the coexistence of different radio systems in the White Space spectrum.

Aspects of the invention alleviate requirements for continuous monitoring of current system states and conditions and automatic reconfiguration of systems. Self-organization capabilities of the system according to aspects of the invention alleviate these tasks.

Aspects of the invention provide a process for automatic spectrum refarming for different RAT systems by determining adequate system states for RAT refarming, determining adequate triggers and measures for changing system states to minimize / avoid overall system degradation during RAT transitions, involving a Network Management System (NMS) as described below with respect to Fig. 10 for implementing decisions on RAT refarming and using a SON coordinator as described below with respect to Fig. 10 that decides on RAT refarming and uses RAT refarming workflow to trigger implementation actions in NMS. The NMS may have a vendor-specific and a standardized north i/f for multi-vendor scenarios. If a RAT runs out of resources to serve the users' traffic demands, it can first try to hand-over some users to the neighboring cells (a process called load-balancing). However, depending on the overall system load, this measure offers limited capabilities only to avoid severe congestion or overload. Methods and devices for Reallocating spectrum between different RATs according to aspects of the invention offer a new degree of freedom and therefore enhance the set of effective counteraction measures. In essence, it is reasonable to apply dynamic spectrum reallocation after the gains of load-balancing have completely been realized, as the effort imposed on the system required for spectrum allocation is significantly higher than that for load-balancing.

The methods described herein may be implemented as software in a Digital Signal Processor (DSP), in a micro-controller or in any other side-processor or as hardware circuit within an application specific integrated circuit (ASIC).

The invention can be implemented in digital electronic circuitry, or in computer hardware, firmware, software, or in combinations thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

Further embodiments of the invention will be described with respect to the following figures, in which:

Fig. 1 shows a schematic diagram of a method 100 for managing communications according to a first radio access technology and according to a second radio access technology according to an implementation form;

Fig. 2 shows a spectral diagram 200 illustrating an assignment of a flexible frequency band according to a method for managing communications according to a first radio access technology and according to a second radio access technology according to an implementation form;

Fig. 3 shows a state diagram 300 of a method for managing communications according to a first radio access technology and according to a second radio access technology according to an implementation form;

Fig. 4 shows a flowchart diagram 400 of a method for managing communications according to a first radio access technology and according to a second radio access technology according to an implementation form;

Fig. 5 shows a flowchart diagram 500 of a method for managing communications according to a first radio access technology and according to a second radio access technology according to an implementation form;

Fig. 6 shows a diagram representing a test scenario 700 for a method for managing communications according to a first radio access technology and according to a second radio access technology according to an implementation form;

Fig. 7 shows a performance diagram 800 of a method for managing

communications according to a first radio access technology and according to a second radio access technology according to an implementation form;

Fig. 8 shows a performance diagram 900 of a method for managing

Fig. 9 shows a performance diagram 1000 of a method for managing

communications according to a first radio access technology and according to a second radio access technology according to an implementation form; Fig. 10 shows a block diagram of a radio network 1 100 with a network entity 1 1 01 for managing communications according to a first radio access technology and according to a second radio access technology according to an implementation form; and

Fig. 1 1 shows a sequence diagram 1200 illustrating information exchange between a network management system and a network entity for managing communications according to a first radio access technology and according to a second radio access technology according to an implementation form.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Fig. 1 shows a schematic diagram of a method 100 for managing communications according to a first radio access technology (RATI ) and according to a second radio access technology (RAT2) according to an implementation form.

A first dedicated frequency band (DB1 ) is assigned for communications according to the first radio access technology (RATI ) and a second dedicated frequency band (DB2) is assigned for communications according to the second radio access technology (RAT2). The method comprises: assigning 101 a flexible frequency band (FB) either for communications according to the first radio access technology (RATI ) or for communications according to the second radio access technology (RAT2).

Fig. 2 shows a spectral diagram 200 illustrating an assignment of a flexible frequency band (FB) according to a method for managing communications according to a first radio access technology (RATI ) and according to a second radio access technology (RAT2) according to an implementation form. An operator is operating two radio access technologies (RATs), namely LTE (RATI ) and UMTS/HSDPA (RAT2) according to this implementation form, in its sites. Two bands of 5 MHz spectrum (dedicated bands, DB1 , DB2) are assigned to LTE and UMTS. In addition, a 5 MHz spectrum band (flex band, FB) can be assigned to any of the RATs according to their specific traffic loads and demands. Flexible band (FB) can be dynamically exchanged between LTE and UMTS. This scenario is of particular importance in emerging phase of LTE: Currently many UMTS smart phones are operating without support for LTE. With population growth of LTE smart phones, in near future it is likely to observe an uneven traffic demand between LTE and UMTS devices, especially in hot spot areas. With applying dynamic spectrum management, operators can provide the desired service in peak traffic hours or places.

User terminals with best-effort traffic will operate either in LTE or in UMTS mode. The reference case which Fig. 2 describes is that LTE and UMTS are each in fixed bands with fixed power. LTE frequency band is dedicated frequency band 1 (DB1 ) and UMTS frequency band is dedicated frequency band 2 (DB2). The middle frequency band, i.e. the flexible frequency band (FB, flex band) of Fig. 2 is used for spectrum sharing, it may be used by both, the LTE and the UMTS system.

Exemplary characteristics of the best-effort users are:

- Each user is guaranteed a minimum rate

r_min(LTE) = 50 kbit /s,

r_min(UMTS) = 30 kbit /s;

- Results in minimum number of resources is required for rate guarantee;

- If resources are remaining, they are equally shared between users, increasing the rate of each user;

- However, maximum rate per user is limited to 1 Mbit/s (LTE) and 0.5 Mbit/s (UMTS). Fig. 3 shows a state diagram 300 of a method for managing communications according to a first radio access technology and according to a second radio access technology according to an implementation form.

For transferring the flex band (FB) from one RAT to the other four states (State 1 , State 2, State 3, State 4) are defined which is illustrated in Fig. 3. Each state represents a system situation. State one (State 1 ) and two (State 2) are the main states of the system. State one (State 1 ) represents the RAT which only operates on 5 MHz dedicated band (DB). State two (State 2) characterizes the RAT which can balance its traffic in both DB and FB. State three (State 3) and state four (State 4) are the transition states for moving from state one (State 1 ) to state two (State 2) and vice versa, respectively. In fact, states three (State 3) and four (State 4) prepare the FB for reallocation from one RAT to the other. The transition of flex band (FB) should be done in a way that increases the operator's utility. For this purpose, a module, called dynamic spectrum manager (DSM) is used.

For reallocating flex band (FB) it is necessary to monitor information from both RATs on their current system conditions. Therefore, a dynamic spectrum manager (DSM) is integrated as a network entity in the network management system (NMS) architecture as described below with respect to Fig. 10. The NMS monitors the status of the RATs and sets off alerts according to conditions that may impact the system performance. The amount of free resources in the dedicated band (DB) is defined, as one of the status or key performance indicator (KPI). The condition for alerting the DSM module is defined as reduction of free resources to a certain amount of value. The DSM module contains two phases of action. The first phase of DSM has proactive characteristics and tries to avoid crisis before it happens. The second phase has reactive characteristics; it tries to manage the occurred crisis in case the proactive phase fails to prevent it. The crisis is defined as overloading of a RAT. Our methodology for the proactive phase is to identify cues of an impending crisis and apply activities that will be carried out to avert it. The proactive phase of the crisis plan should identify the triggers that typically set off a crisis. Successful proactive action can eliminate the need for reactive crisis responses. The reactive phase of the DSM represents how to manage the occurred actual crisis and return the system to a desired situation, which is here solving the overload situation.

Fig. 4 shows a flowchart diagram 400 of a method for managing communications according to a first radio access technology and according to a second radio access technology according to an implementation form.

Figure 4 illustrates the proactive part of the DSM in form of a flowchart diagram. Ellipse is used for showing states, rectangle is used for actions, rhombus as conditional branches. At initial stage RATI (LTE) is operating in 5 MHz dedicated band (state 1 ) and RAT2 (HSDPA) owns the flex band (state 2). NMS continuously monitors the amount of free resources as the key performance indicator in RATI and provides alerts for DSM if the KPI falls below a certain threshold, 401 . A dynamic threshold is applied for identifying cues of an impending crisis. The threshold is defined as:

where At is a time interval and ·¾ is the effective arrival rate of users in RATI . The effective arrival rate is defined as:

where P is the measured user arrival of LTE in a cell and v-i is the measured rate of users that leave LTE resources in the cell. -^Γ^* is the average amount of the necessary resources required for serving a single user with minimum quality of service. Therefore, is the amount of necessary resources that RATI needs in order to serve the users requesting service during the next At minutes. By violation of the KPI, it is indicated that RATI is running out of resources. Hence, NMS alerts the DSM module, the DSM oversees the situation in both RATs for reallocating the FB by evaluating a utility function, 403. A utility function U, 403 is determined in order to measure the change in the total relative load in the system caused by band reallocation. The relative load is defined as the amount of consumed resources normalized to the amount of available resources in a RAT; and the total relative load is the summation of LTE and HSDPA's relative load. With evaluating the total relative load the total amount of available resources as sum over both RATs is maximized. Therefore, the sum of relative loads over both RATs is minimized. A utility function U is defined that serves the mentioned aim. By evaluating the utility function, 403, DSM decides about reallocation of the FB. The utility function is defined as:

where ^li and ¾ are the current relative loads on RAT 1 and RAT 2. For statistical purposes, the load over its history is averaged. ^ ⁴ and are the relative loads on dedicated band of RAT 1 and RAT 2 after exchanging the FB. In our scenario, RAT 2 is already using the FB. After reassigning the FB to RAT 1 , the load on the DB of RAT 2 doubles, i.e.

This is because user served on the FB will be moved to the DB. Correspondingly, the load on DB of RAT 1 reduces to half the value, A positive utility function represents: By exchanging the flex band the summation of the relative load of HSDPA and LTE on the system decreases. In other words, if the present total relative load + ^lz ) is larger than the estimated future total load

+ ), reallocating of the flex band helps to balance the relative load on the system and prevents the impending overload in RATI . Following figure 4, if the utility function is a positive number, 405, FB will be closed to new users, 407 in RAT 2 and a timer is set, 409. With this action the necessary time for RAT 2 to prepare the FB for releasing is provided and the possibility is given to the users in the FB to end their session without the need for a handover (for example radio resource manager could be configured so that users with nearly empty queue may get more resources to end their sessions). After elapsing the indicated time, RAT 2 is set to state 4, 41 1 if and only if U > 0, 405. At this state RAT 2 hands over the remaining users in FB to DB, 413 in order to free the FB, 415. Once the FB is freed, the state of RAT 2 is changed to state 1 , 417. In response RAT 1 is switched to state 3, 419 to configure the FB for its use, 421 .

After finalizing the configuration, RAT 1 will change to state 2, 423 and balance its users on both the DB and the FB. Accordingly, RAT 1 and RAT 2 have swapped their states.

On the other hand, if the utility function U is negative, 431 , the reallocation of the flex band causes the total relative load on the system to increase. Therefore the DSM does not reallocate the FB. Thereupon, with updating the KPI's threshold, 433 to a lower amount time is given to the system to develop further. Reducing the threshold can be done by decreasing At in equation (1 ). The successive violation of the updated threshold represents RATI is approaching to the overload level. If the amount of free resources in RATI falls below the lowest threshold, it indicates that RAT 1 completely ran out of resources and the DSM triggers the reactive section as will be described below with respect to Fig. 5. With applying reactive section the overload is handled and solved.

Fig. 5 shows a flowchart diagram 500 of a method for managing communications according to a first radio access technology and according to a second radio access technology according to an implementation form.

Figure 5 illustrates the reactive section in DSM. Triggering the reactive section means RATI is overloaded and is in need of additional resources. But before granting the FB to RATI , it is checked that the reallocation of the flex band improves the overall situation. Before band reallocation it is necessary to check the amount of free resources in dedicated band of RAT2, 501 . The amount of free resources should be large enough in order to accommodate the current users in the FB plus the future users arriving during a predefined time interval &^tfiit . This value is calculated as follows: φ™ :Υ·- ^{:': ■} i * Δί-^ As - f ?s

where N^flex is the number of current users in the flex band. If the amount of free resources in DB of RAT2 is larger than Ψ the FB is closed to new users, 503 and the timer, 505 is set. Meanwhile RAT2 prepares the FB for releasing. Thereafter the blocking rate of RAT 1 , 507 is checked. If it is larger than the indicated threshold, the total relative load and overload of the system after band reallocation is evaluated. The utility function is extended in equation (3) in order to measure the amount of change in total relative load and overload in the system caused by band reallocation. The extended utility function, 509 can be described as:

where θ₁ and 6₂are the overloads in RATI and RAT2. ^ ^'^ is the predicted overload during next minutes after RATI obtains the flex band,

where ^Q: is the resources necessary for serving future users during next ^&i' "^r minutes. The future time interval

be chosen in a way that the assumed future effective user arrival rate ·- . does not change significantly over ^ ^¾f minutes. is the amount of free resource in both the DB and the FB; and ^g is the total amount of resources in RAT 1 . ⁸l^{' ::h} is the predicted overload during next minutes after RAT 2 release the flex band,

where β is the resources necessary for serving future users during next &^{t iit} minutes plus the resources necessary for serving the current users in the flex band.

2 is the amount of free resource in the DB of RAT 2 and % *^&ί is the total amount of resources in RAT 2.

A negative (extended) utility function, 51 1 represents: By exchanging the FB, the total relative load and probable overload on the system will increase. So the system is not triggered to change the FB. A positive utility function, 513 on the other hand represents the total relative load and probable overload will be relaxed by band reallocation. After obtaining all the necessary conditions for band reallocation, RAT 2 is set to state 4, 515 and handover all the current users, 517 in the FB to the DB and subsequently RAT 2 is set to state 1 , 519. Afterwards RATI shifts to state 3, 521 and prepares the FB for the new users, 523. After finalizing the configuration, RAT 1 will change to state 2, 525 and balance its users on both the DB and the FB. Accordingly, RAT 1 and RAT 2 have swapped their states.

Fig. 6 shows a diagram representing a test scenario 700 for a method for managing communications according to a first radio access technology and according to a second radio access technology according to an implementation form.

Simulation results are used for demonstration purpose. The advantage of the DSM is demonstrated by depicting the performance of the system both with and without applying the DSM, for a typical hotspot scenario, and by comparing them respectively. Furthermore, for illustrating the advantage of the DSM, the number of served users with and without applying the DSM is counted and compared.

The scenario is simulated in a system-level. Environment model consists of a multi-cell scenario with 48 macro cells and all cells are of equal size. LTE and UMTS are operated at each site simultaneously, i.e. two radio access technologies (RATs) are operated in each cell, wherein one is according to LTE standard and the other is according to UMTS standard. FTP traffic is modelled, according to the frequently used FTP model introduced in "3GPP, "Feasibility study for orthogonal frequency division multiplexing for UTRAN enhancement," TR 25.892, V 6.0.0, 2004-06". A constant number of uniformly distributed users (background users) with infinite data queue are moving through the operator's playground, constituting the basic system load. An average number of 20 users per RAT in each cell is defined. Hot spot covers a single cell (the center cell), and the velocity of the users in the hot spot is set to pedestrian speed, i.e. about 3 km/h. New users enter to the playground with constant arrival rate λ. The user arrival rate is modeled by a Poisson distribution with A_LTE = 8 users/min and AUMTS = 4 users/min, i.e. LTE and HSDPA user arrival rate in hotspot is set to 8 and 4 users per minute, respectively. FTP traffic supporting a scalable data rate is assumed. The data rate depends on the number of users simultaneously served in the cell. The average number of packets per session is set to 5, their distribution is modeled as a Poisson distribution. The size of the packets is modeled as truncated log-normal distribution with a mean of 2 Mbytes. As the total number of available resources needs to be shared between all the users, the allocated user data rate decreases with increasing number of users.

However, to ensure that the data transmission of a user does not fall below a limit, a minimum data rate is guaranteed for each FTP user. The minimum rate for each user is 50 kbit/s in the LTE system and 30 kbit/s in the UMTS system. Furthermore, in order to avoid that a single user occupies too many resources, its data rate is also bound to a maximum. For LTE, maximum data rate is limited to 1 Mbit/s and 500 kbit/s for UMTS.

Fig. 7 shows a performance diagram 800 of a method for managing

communications according to a first radio access technology and according to a second radio access technology according to an implementation form for the test scenario of Fig. 6.

Figure 7 shows the loads on LTE and HSDPA system separately for the hot spot cell described above with respect to Fig. 6,

LTfc^'s k>¾J ... i; M¾_; I D

Lines with circle marker, i.e. line 802 for HSDPA and 804 for LTE, demonstrate the system load without applying the DSM. In this scenario FB is constantly allocated to the HSDPA system. At t = 1 1 min the DB of LTE is fully loaded (100%) and starts to block new users. As a result, load on the LTE passes 100% and reaches to 150% (50 percent overload). At the same time just 20% of HSDPA's resources is used, furthermore it is using FB. The DSM scenario is shown with squared markers lines, i.e. 801 for HSDPA and 803 for LTE, in Figure 7. FB initially is allocated to UMTS, the RAT equally balances the users in both DB and FB. The load on both RATs is continuously increasing. At time equal to 6 minutes, LTE uses about 60 percent of available resources in the dedicated band. In order to balance the total relative load and preventing probable overload, the proactive section of DSM is triggered and reallocates the FB to the LTE. Accordingly, HSDPA hands over all users from FB to the DB. The jump in load of HSDPA is the result of this handover. On the other hand, LTE, after obtaining the FB, balances its load on both bands by handing over the users from DB to FB. Thus the overload in LTE is effectively prevented by applying DSM and no user is blocked.

Fig. 8 shows a performance diagram 900 of a method for managing

Figure 8 shows the operator's averaged overall relative load in the hot spot cell according to

The first curve 901 is the load history of the operator during one hour without applying dynamic spectrum management (DSM). The second curve 902 shows the load history of the operator with applying dynamic spectrum management. The averaged total relative load on the operator's RATs is significantly decreased when DSM is applied.

Fig. 9 shows a performance diagram 1000 of a method for managing

Figure 9 shows the total number of users served by RAT 1 and RAT 2 in the hot spot cell. Served users represent the number of users that successfully terminated their session during the operation time plus the number of users currently served by the system. The first curve 1001 depicts the number of served users when dynamic spectrum management (DSM) is not applied. The second curve 1002 depicts the number of served users when dynamic spectrum management (DSM) is applied. It is clearly seen that by applying the DSM approach, a significantly higher number of total users can be served.

The method as described with reference to Figures 1 to 9 provides a concept for sharing the spectrum between two different RATs in an intra-operator scenario. The presented methodology consists of two complimentary phases, the proactive phase and reactive phase. The proactive phase of this methodology represents how to avoid potential overload in RATs; and the reactive phase expresses how to manage an actual overload in case the proactive phase fails to avoid it. The simulation results illustrate that with applying the proposed dynamic spectrum management overload in RATs can be effectively prevented and the operator's overall load can be effectively balanced. Furthermore, a higher number of total users can be served by applying the DSM. The simulation results confirm that the designed dynamic spectrum manager is a useful reference for intra-operator spectrum management plans.

Fig. 10 shows a block diagram of a radio network 1 100 with a network entity 1 101 for managing communications according to a first radio access technology RATI and according to a second radio access technology RAT2 according to an implementation form. The network entity 1 101 comprises a coordination processor (SON coordinator) 1 103 serving as the policy machine which comprises a workflow engine 1 105 processing a Business Process Execution Language. The SON coordinator 1 103 is coupled by a coordination interface 1 131 which is also an interface of the network entity 1 101 to a Network Management System (NMS) 1 121 . The SON coordinator 1 103 is coupled by a first interface 1 135 to an external radio network planning unit 1 107 providing planning data for the external radio network, by a second interface 1 137 to a coverage optimization unit 1 109 providing the workflow for coverage optimization and by a third interface 1 139 to a RAT refarming unit 1 1 1 1 providing the workflow for RAT refarming.

The network management system (NMS) 1 121 comprises a Software License Managing Unit 1 123, a Configuration Management (CM) unit 1 125, a Performance Monitoring (PM) Unit 1 127 and a Fault Monitoring (FM) unit 1 129. The network management system (NMS) 1 121 is coupled by the coordination interface 1 131 to the coordination processor 1 103 of the network entity 1 101 . The network management system (NMS) 1 121 is coupled by a network management interface 1 133 to external radio and core network elements 1 141 . The network

management interface 1 133 may be a vendor-specific interface, it may be a North interface for multi-vendor environments. Information from network elements 1 141 can be collected across multi-vendor platforms and provided to NMS 1 121 through the north i/f 1 133.

According to some implementation forms, an operator owns a multiple RAT system, which are under the common control of a network management system (NMS) 1 121 . The NMS 1 121 monitors the current system conditions in all RATs and allows reconfiguring each RAT system. In case one of the RATs (say RAT 1 ) experiences a high traffic load which may drive RAT 1 into status of

congestion/overload, this can be detected by the NMS 1 121 by observing corresponding key performance indicators (KPI) provided by RAT 1 . By

reallocating the resources assigned to the different RATs through the reconfiguration module of the NMS 1 121 , the critical situation in RAT 1 can be resolved. By applying the network entity 1 101 , the reallocation process is facilitated such that the problem is not simply shifted from one RAT to another. The network entity 1 101 dynamically reallocates spectrum to solve potential situations of overload that occurred in one of the operator's RATs. A dynamic spectrum manager (DSM) fulfilling the task of automated spectrum refarming is used. The DSM can be facilitated as a function within the SON coordinator 1 103, which may advise the NMS 1 121 to reconfigure the corresponding RAT systems if a decision for reallocation has been taken.

The network entity 1 101 is used for managing communications according to a first radio access technology RATI and according to a second radio access technology RAT2, wherein a first dedicated frequency band DB1 is assigned to the first radio access technology RATI and a second dedicated frequency band DB2 is assigned according to the second radio access technology RAT2. The

coordination processor 1 103 is used for processing an assignment of a flexible frequency band FB either for communications according to the first radio access technology RATI or for communications according to the second radio access technology RAT2. The coordination processor 1 103 is configured to perform a method as described with respect to Figures 1 to 9. The coordination interface 1 131 is coupleable to the network management system 1 121 . The network management system 1 121 is configurable to receive the assignment processed by the coordination processor 1 1 03 and to assign the flexible frequency band FB according to the assignment processed by the coordination processor 1 103. The coordination interface 1 1 31 is configured to transmit a key performance indicator (KPI) indicating an amount of free resources in the first dedicated frequency band DB1 or an amount of free resources in the second dedicated frequency band DB2 to the coordination processor 1 103.

The network entity 1 101 performs dynamic spectrum management (DSM) as described above with respect to Figures 1 to 5. RAT refarming steps are planned in the RAT refarming unit 1 1 1 1 and the RAT refarming algorithm, which

corresponds to the method described above with respect to Figures 1 to 5, is executed in the coordination processor (SON coordinator) 1 103. The RAT refarming implementation with respect to the assigning of frequency bands is performed in the Configuration Management unit 1 125 of the NMS 1 121 . The KPI monitoring is performed in the Performance Monitoring unit 1 127 of the NMS 1 121 . SON coordinator 1 103 and NMS 1 121 may be provided by different providers or vendors. Therefore, an exemplary specification of communication flow between the two entities 1 103 and 1 121 is illustrated in Fig. 1 1 .

PM unit 1 127 continuously monitors adequate KPIs per RAT per cell, e.g.

• Number of currently admitted terminals in the cell,

• Increase in admitted terminals (effective user arrival rate), which can be used to predict future user behavior in cell,

• Number of dropped and blocked calls (indicating system overload),

• Amount of the total resources used to guarantee all users QoS.

A two-phase counteraction approach is performed by SON coordinator 1 103 to allow for an early handling of occurring problems

• Phase 1 : Proactive approach

If it can be foreseen that a RAT may run into situation of overload, band reallocation is prepared and carried out if no other RAT is negatively affected. Otherwise problem handling will be escalated by setting new KPI alarm level.

• Phase 2: Reactive approach

If the proactive approach could not solve the situation and the system runs into a situation of overload, band reallocation is forced after ensuring that no other RAT will be driven into overload situation after reallocation. In an implementation form , the algorithm for automated spectrum refarming is as follows:

• For a scenario where one operator operates different RATs in the same network, one RAT may borrow spectrum from the other. As the operator has full control over both RATs, he can directly free and occupy single frequency bands by actively shifting/admitting users to a desired frequency band. Once a band is freed, it can be allocated to another RAT and reconfigured for its use.

• To identify if a RAT requires additional spectrum, a SON function for RAT refarming is implemented in SON coordinator 1 103 that monitors KPIs (by PM module 1 127 of NMS 1 121 ) and triggers a spectrum reallocation (SR) request (carried out by CM module 1 125 of NMS 1 121 ) if a threshold for one of these KPIs is exceeded.

• After SR request, the costs for both RATs are assessed (in SON coordinator 1 103) for the two cases:

• Case 1 : SR request is rejected -> no spectrum reallocation

• Case 2: SR request is granted -> spectrum is freed by RAT 2 and reallocated to RAT 1

For cost estimation, historical data on the system conditions and KPIs will be used.

After comparing the costs, a decision is taken by SON coordinator 1 103 and steps defined by the workflow for RAT refarming 1 1 1 1 are taken, if necessary.

Fig. 1 1 shows an exemplary sequence diagram illustrating information exchange between a network management system (NMS) comprising a configuration management (CM) unit 1 125 and a performance management (PM) unit 1 127 and a network entity 1 101 for managing communications according to a first radio access technology RATI and according to a second radio access technology RAT2 according to an implementation form as described with respect to Fig. 10, where the network entity 1 101 comprises a coordination processor (SON

coordinator) 1 103.

At the beginning, RATI is in state 1 and RAT2 is in state 2. According to the state diagram depicted in Fig. 3, only the dedicated band DB1 is allocated for RATI while the dedicated band DB2 and additionally the flexible frequency band FB is allocated for RAT2. A first message 1201 "KPI reporting (both RATs)" is sent from PM unit 1 127 (cf. Fig. 9) to SON coordinator 1 103 (cf. Fig. 9) indicating that RATI lacks resources. The SON coordinator 1 103 calculates the utility function U as being greater than zero. A cost evaluation results that a spectrum reallocation (SR) can be granted. Thus, a second message "close flex band for RAT2" 1203 is sent from SON coordinator 1 103 to CM unit 1 125 (cf. Fig. 9) requesting the

configuration management to close the flex band (FB) for RAT2. The second message 1203 is acknowledged by the CM unit 1 125 by the acknowledgement message 1205. After receiving the acknowledgement message 1205, the SON coordinator 1 103 sets a timer. While the timer is running a fourth message "KPI reporting" 1207 arrives from PM unit 1 127 reporting on the key performance indicators (KPI), e.g. reporting on the amount of free resources in the dedicated bands of RATI and RAT2.

When the timer expires, the SON coordinator 1 103 evaluates the utility function U which now has a negative value. A cost evaluation results that a spectrum reallocation (SR) is rejected. Thus, a fifth message "reopen flex band for RAT2" 1209 is sent from SON coordinator 1 103 to CM unit 1 125 requesting the

configuration management to reopen the flex band (FB) for RAT2. Then, a sixth message "hand over all users in flex band of RAT2" 121 1 is sent from SON coordinator 1 103 to CM unit 1 125 requesting the configuration management to hand over all users in flex band (FB) of RAT2. When the utility function U indicates a positive value and a cost evaluation results that a spectrum reallocation (SR) can be granted, RAT2 changes to state 4 in which the flex band is going to be released. Upon receiving a seventh message "flex band freed" 1213 from CM unit 1 125, the SON coordinator 1 103 sets RAT2 to state 1 where only the dedicated band is allocated to RAT2. Then RATI is set to state 3 where the flex band is configured and the SON coordinator 1 103 sends an eighth message "Configure flex band for use by RATI " 1215 to CM unit 1 125. When CM unit 1 125 has configured the flex band, it acknowledges the eighth message 1215 by a ninth message "flex band configured" 1217 to SON

coordinator 1 103. Thereupon, SON coordinator 1 103 sets RATI to state 2 where dedicated and flex band are allocated to RATI and sends a tenth message "open flex band for RATI " 1219 to CM unit 1 125.

Implementation forms of the invention provide a dynamic reallocation of spectrum bands between different RATs operated from the same sites by a single operator. Implementation forms of the invention introduce system states and their transition driven by exceeding thresholds of KPIs which are continuously monitored in the involved RATs. Implementation forms of the invention provide mapping of RAT refarming functions to NMS components (PM, CM) and SON coordinator (cf. Figs. 10 and 1 1 ) and specification of information exchange between these entities (cf: Fig. 1 1 ). Note that SON coordinator or NMS could come from a 3rd party. The RAT refarming algorithm (corresponding to the method as described with respect to Figures 1 to 5) provides triggering of countermeasures if KPI thresholds are exceeded and using a timer after closing the flex band, thereby enabling to observe altered system behavior before taking the final decision to reallocate the flex band. The timer indicates the specific time the flex band is closed before reallocation of the flex band. Thus the RAT is given time to prepare for hand-over of users in flex band and observing altered system behavior in dedicated band is enabled before the final decision to reallocate flex band is taken. Aspects of the invention introduce a process for automatic spectrum refarming for different RAT systems by defining adequate system states for RAT refarming and by defining adequate triggers and measures for changing system states to avoid or at least minimize overall system degradation during RAT transitions.

The Network Management System (NMS) is involved for implementing decisions on RAT refarming. The SON coordinator decides on RAT refarming and uses the RAT refarming workflow to trigger implementation actions in NMS. NMS has vendor-specific and a standardized north i/f for multi-vendor scenarios.

General purpose computers may implement the foregoing methods and computer programs, in which the computer housing may house a CPU (central processing unit), memory such as DRAM (dynamic random access memory), ROM (read only memory), EPROM (erasable programmable read only memory), EEPROM

(electrically erasable programmable read only memory), SRAM (static random access memory), SDRAM (synchronous dynamic random access memory), and Flash RAM (random access memory), and other special purpose logic devices such as ASICs (application specific integrated circuits) or configurable logic devices such GAL (generic array logic) and reprogrammable FPGAs (field programmable gate arrays).

Each computer may also include plural input devices (for example, keyboard, microphone and mouse), and a display controller for controlling a monitor.

Additionally, the computer may include a floppy disk drive; other removable media magneto optical media); and a hard disk or other fixed high-density media drives, connected using an appropriate device bus such as a SCSI (small computer system interface) bus, and Enhanced IDE (integrated drive electronics) bus, or an Ultra DMA (direct memory access) bus. The computer may also include a compact disk reader, a compact disk reader/writer unit, or a compact disc jukebox, which may be connected to the same device bus or to another device bus. The invention envisions at least one computer readable medium. Examples of computer readable media include compact discs, hard disks, floppy disks, tape, magneto optical disks, PROMs (for example, EPROM, EEPROM, Flash EPROM), DRAM, SRAM, SDRAM. Stored on any one or on a combination of computer readable media is software for controlling both the hardware of the computer and for enabling the computer to interact with other elements, to perform the functions described above. Such software may include, but is not limited to, user

applications, device drivers, operating systems, development tools, and so forth. Such computer readable media further include a computer program product including computer executable code or computer executable instructions that, when executed, causes a computer to perform the methods disclosed above. The computer code may be any interpreted or executable code, including but not limited to scripts, interpreters, dynamic link libraries, Java classes, complete executable programs, and the like.

From the foregoing, it will be apparent to those skilled in the art that a variety of methods, systems, computer programs on recording media, and the like, are provided.

The present disclosure also supports a computer program product including computer executable code or computer executable instructions that , when executed, causes at least one computer to execute the performing and computing steps described herein.

The present disclosure also supports a system configured to execute the performing and computing steps described herein.

Many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the above teachings. Of course, those skilled in the art readily recognize that there are numerous applications of the invention beyond those described herein. While the present inventions has been described with reference to one or more particular embodiments, those skilled in the art recognize that many changes may be made thereto without departing from the scope of the present invention. It is therefore to be understood that within the scope of the appended claims and their equivalents, the inventions may be practiced otherwise than as specifically described herein.

Claims

CLAIMS:

1 . Method (100) for managing communications according to a first radio access technology (RATI ) and according to a second radio access technology (RAT2), wherein a first dedicated frequency band (DB1 ) is assigned for

communications according to the first radio access technology (RATI ) and a second dedicated frequency band (DB2) is assigned for communications

according to the second radio access technology (RAT2), the method comprising: assigning (101 ) a flexible frequency band (FB) either for communications

according to the first radio access technology (RATI ) or for communications according to the second radio access technology (RAT2).

2. The method (100) of claim 1 , comprising: monitoring, in particular continuously monitoring, a key performance indicator (KPI) indicating an amount of free resources in the first dedicated frequency band (DB1 ); and assigning the flexible frequency band (FB) for communications according to the first radio access technology (RATI ) if the key performance indicator (KPI) crosses a predetermined threshold (KPIviolated); or monitoring, in particular continuously monitoring, a key performance indicator (KPI) indicating an amount of free resources in the second dedicated frequency band (DB2); and assigning the predetermined flexible frequency band (FB) for

communications according to the second radio access technology (RAT2) if the key performance indicator (KPI) crosses a predetermined threshold (KPIviolated).

3. The method (100) of claim 2, wherein the key performance indicator (KPI) is represented by the amount of free resources in the system, and the threshold is determined by the future demand of additional resources.

4. The method (100) of anyone of the preceding claims, wherein the flexible frequency band (FB) is assigned for communications according to the first radio access technology (RATI ), and wherein the method comprises handing over users communicating in the flexible frequency band (FB) according to the first radio access technology (RATI ) to the first dedicated frequency band (DB1 ) to free the flexible frequency band (FB) if additional communication resources are required for communications according to the second radio access technology (RAT2), and assigning the flexible frequency band (FB) for

communications according to the second radio access technology (RAT2); or wherein the flexible frequency band (FB) is assigned for communications according to the second radio access technology (RAT2), and wherein the method comprises handing over users communicating in the flexible frequency band (FB) according to the second radio access technology (RAT2) to the second dedicated frequency band (DB2) to free the flexible frequency band (FB) if additional communication resources are required for communications according to the first radio access technology (RATI ), and assigning the flexible frequency band (FB) for

communications according to the first radio access technology (RATI ).

5. The method (100) of anyone of the preceding claims, further comprising determining a utility function (U), the utility function (U) indicating a change of a communication load due to an assignment of the flexible frequency band (FB) to one of either the first radio access technology (RATI ) or the second radio access technology (RAT2); and assigning the flexible frequency band (FB) either for communications according to the first radio access technology (RATI ) or for communications according to the second radio access technology (RAT2) only if the utility function (U) fulfils a utility criterion.

6. The method (100) of claim 5, wherein the utility criterion is fulfilled if the utility function (U) is equal to or greater than a utility threshold.

7. The method (100) of one of the preceding claims, wherein the first radio access technology (RATI ) comprises a UMTS technology and the second radio access technology (RAT2) comprises an LTE technology or wherein the first radio access technology (RATI ) comprises an LTE technology and the second radio access technology (RAT2) comprises a UMTS technology.

8. The method (100) of one of the preceding claims, wherein each of the first dedicated frequency band (DB1 ), the second dedicated frequency band (DB2) and the flexible frequency band (FB) comprises a 5 MHz spectrum band.

9. The method (100) of one of the preceding claims, wherein the assigning is performed automatically.

10. The method (100) of one of the preceding claims, wherein the assigning is performed dynamically.

1 1 . Network entity (1 101 ) for managing communications according to a first radio access technology (RATI ) and according to a second radio access technology (RAT2), wherein a first dedicated frequency band (DB1 ) is assigned to the first radio access technology (RATI ) and a second dedicated frequency band (DB2) is assigned to the second radio access technology (RAT2), the network entity (1 101 ) comprising: a coordination processor (1 103) for processing an assignment of a flexible frequency band (FB) either for communications according to the first radio access technology (RATI ) or for communications according to the second radio access technology (RAT2).

12. The network entity (1 101 ) of claim 1 1 , wherein the coordination processor (1 103) is configured to perform a method according to one of claims 1 to 10.

13. The network entity (1 101 ) of claim 1 1 or claim 12, further comprising a coordination interface (1 131 ) coupleable to a network management system (1 121 ), the network management system (1 1 21 ) being configurable to receive the assignment processed by the coordination processor (1 103) and to assign the flexible frequency band (FB) according to the assignment processed by the coordination processor (1 103).

14. The network entity (1 101 ) of claim 13, wherein the coordination interface (1 131 ) is configured to transmit a key performance indicator (KPI) indicating an amount of free resources in the first dedicated frequency band (DB1 ) or an amount of free resources in the second dedicated frequency band (DB2) to the

coordination processor (1 103).

15. Computer program for implementing the method (100) according to one of claims 1 to 10.