WO2018050251A1

WO2018050251A1 - Method and estimation node for estimating load

Info

Publication number: WO2018050251A1
Application number: PCT/EP2016/072172
Authority: WO
Inventors: Carlos UBEDA CASTELLANOS; José Manuel MOSTAZA TAVIRA; Jose OUTES CARNERO; Lorena RIOS SEPULVEDA
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2016-09-19
Filing date: 2016-09-19
Publication date: 2018-03-22

Abstract

A method and an estimation node for estimating load on a plurality of cells of a cellular network are disclosed. The estimation node (140) obtains (A010) RSRP, RS- SINR, RSTD and PCI for said plurality of cells (101 -103). The estimation node (140) determines (A090) a respective alpha coefficient and a respective beta coefficient based on the PCI, the RSTD, a symbol duration, rho_A and rho_B for each pair of said plurality of cells (101-103). Both rho_A and rho_B scale transmit power compared to transmit power of REs carrying CRSs. Moreover, the estimation node (140) sets up (A100) a system of linear equations. The linear system relates load of the plurality of cells (101 - 103) to the RSRP and the RS-SINR of the plurality of cells (101 -103). Furthermore, the estimation node (140) provides (A130) a respective value indicating load of each cell (101, 102, 103) by solving the system of linear equations with respect to load. A corresponding computer program and a computer program carrier are also disclosed.

Description

METHOD AND ESTIMATION NODE FOR ESTIMATING LOAD

TECHNICAL FIELD

Embodiments herein relate to wireless communication networks, such as telecommunication networks, cellular networks or the like. In particular, a method and an estimation node for estimating load on a plurality of cells of a cellular network are disclosed. A corresponding computer program and a computer program carrier are also disclosed. BACKGROUND

With reference to a telecommunication network, the term "cell load", or "load in a cell", typically refers to an amount of power or an amount of time/frequency resources that are consumed during a certain time instant in relation to an amount of power or time/frequency resources that is available in a cell of the telecommunication network. Cell load rises with interference, which e.g. may result from increase of traffic in e.g. so called neighboring cells that are located in a vicinity of the cell for which load is to be estimated. Upon an increase of the load, there may be a risk of service outage and/or a general performance degradation of the telecommunication network. Therefore, the network can take advantage of estimations of cell load in real time in order to make radio resource management decisions, e.g. related to load balancing, handover, etc. In this manner, user experience may be improved since service outage and/or the general performance degradation may be avoided thanks to suitable radio resource management decisions. Thus, cells are prevented from being overloaded.

On the other hand, estimations of cell load may be derived from drive-tests (or any other monitoring device). These estimations of cell load can be used by Network Design and Optimization (NDO) tools for Radio Frequency (RF) shaping, capacity dimensioning, network troubleshooting, etc. In a known Long Term Evolution (LTE) network, Orthogonal Frequency Division

Multiple Access (OFDMA) is employed as multiplexing scheme in LTE downlink. As described by 3GPP, "Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Physical channels and modulation", Technical Specification (TS) 36.211 , V13.1.0, March 2016, a so called Resource Element (RE) is defined as a frequency-time combination of one 15 kHz subcarrier in frequency domain and one symbol duration in time domain. REs are grouped into Physical Resource Blocks (PRBs). A PRB includes 12 consecutive subcarriers in the frequency domain and 7 symbols for normal cyclic prefix (or 6 symbols for extended cyclic prefix), which is equivalent to 1 slot of 0.5 ms in the time domain. For normal cyclic prefix, a symbol typically has a useful symbol time of 66.7 microseconds, thus excluding the cyclic prefix.

In order to facilitate downlink channel estimation, Cell-specific Reference Signals (CRSs) are transmitted in every PRB. The CRSs are transmitted according to a specific time-frequency pattern. Known concepts in LTE include a number of antenna ports, a cyclic prefix and a Physical Cell Identity (PCI). The number of antenna ports and the cyclic prefix determine in which symbols the CRSs are transmitted, while the PCI determines in which subcarriers the CRSs are transmitted. In particular, the exact subcarrier is shifted according to PCI mod 6. According to the above mentioned 3GPP TS 36.21 1 , the PCI is obtained after decoding the synchronization signals. Figure 1 illustrates an example of a CRS pattern on two PRBs over a sub-frame, aka 2 slots, for different antenna ports and normal cyclic prefix. REs used for CRSs are striped horizontally, REs marked with an X are not used, with the purpose of reducing inter- antenna interference, and the remaining REs, "non-CRS REs", are mainly available for user data.

Moreover, a so called Reference Signal Received Power (RSRP) is specified in 3GPP "Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer; Measurements", TS 36.214, V13.1.0, March 2016, is defined as a linear average over power contributions of those REs that carry CRSs within a measurement frequency bandwidth for which cell load is to be estimated. In order to have a substantially constant power for all symbols such that power variations at the User Equipment (UE) are minimized, the transmit power of non- CRS REs that are sent in symbols in which CRSs are not present (type A) is scaled by a factor p^(A) compared to the transmit power of REs carrying CRSs, while the transmit power of non-CRS REs that are sent in symbols including CRSs (type B) is scaled by a factor p^(B) compared to the transmit power of REs carrying CRSs (see Figure 1 ). So, the ratio between and p^(A), which is the actual parameter standardized by 3GPP, "Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures", TS 36.213, V13.1.1 , March 2016, will set the received power relation between different REs at the UE. The above mentioned 3GPP TS 36.214 also defines the Reference Signal -

Signal to Noise and Interference Ratio (RS-SINR) as the linear average over the power contribution of the REs carrying CRSs divided by the linear average of the noise and interference power contribution over the REs carrying CRSs within the same frequency bandwidth. Interference from adjacent cells experienced by the CRSs of a given cell is dependent on whether such interference comes from CRSs - i.e. time-frequency collision between CRSs of the observed cell and a neighbor cell - or non-CRS REs - i.e. time- frequency collision between CRSs of the observed cell and non-CRS REs of a neighbor cell. A reason for this dependency is that, firstly, power in CRSs is always transmitted, while power in non-CRS REs is only transmitted when there is available data, i.e.

proportionally to the cell load, and, secondly, power settings differ among REs. A type of collision is not only subject to the PCI assignment, which determines the subcarrier, but also to the time-difference on downlink transmission.

Furthermore, the above mentioned 3GPP TS 36.214 discloses Reference Signal Time Difference (RSTD) performed on Positioning Reference Signals (PRSs) for location-based services. The RSTD is a general measure of time difference between two received signals related to two different cells. Therefore, in case of synchronized networks, such as in Time Division Duplex (TDD) deployments, the time- difference approximates to zero. However, for unsynchronized networks, such as many Frequency Division Duplex (FDD) networks, the time-difference is typically not zero. Figure 2 shows (a) an example of a collision between CRSs in cell #1 with CRSs in cell #2 for a synchronized network and (b) an example of a collision between CRSs in cell #1 with non-CRS REs in cell #2 for an unsynchronized network. A proposal for estimation of cell load is presented in document "Scanner Based

Load Estimation for LTE Networks", to R. P. Wicaksono, et al., laid open at an

International Conference by Information and Communication Technology Convergence (ICTC) in October 2015. This approach averages estimations of cell load associated with each possible combination of PCI and time-difference, such as RSTD, in the downlink transmission weighted by their respective probability. Moreover, this approach assumes the same load for all adjacent cells, or neighbor cells, when estimating the load of a cell under consideration. In some scenarios, this approach may not be accurate enough.

SUMMARY

An object may thus be to improve accuracy of estimation of downlink cell load for a network of the above mentioned kinds, such as synchronized as well as

unsynchronized networks.

According to an aspect, the object is achieved by a method for estimating load on a plurality of cells of a cellular network. The estimation node obtains RSRP, RS-SINR, RSTD and PCI for said plurality of cells. The estimation node determines a respective alpha coefficient and a respective beta coefficient based on the PCI, the RSTD, a symbol duration, p^ and p^(B) for each pair of said plurality of cells. A first cell of said each pair is considered as a reference cell and a second cell of said each pair is considered as an adjacent cell. p^w is used for scaling of transmit power of non-Cell- Specific Reference Signal "non-CRS" Resource Elements "REs" that are sent in symbols in which CRSs are not present, referred to as type A REs. p^(B) is used for scaling of transmit power of non-CRS REs that are sent in symbols including CRSs, referred to as type B REs. Both and p^(B) scale transmit power compared to transmit power of REs carrying CRSs. Moreover, the estimation node sets up a system of linear equations. The linear system relates load of the plurality of cells to the RSRP and the RS-SINR of the plurality of cells. Furthermore, the estimation node provides a respective value indicating load of each cell by solving the system of linear equations with respect to load.

According to another aspect, the object is achieved by an estimation node configured for estimating load on a plurality of cells of a cellular network. The estimation node is configured for obtaining RSRP, RS-SINR, RSTD and PCI for said plurality of cells. The estimation node is further configured for determining a respective alpha coefficient and a respective beta coefficient based on the PCI, the RSTD, a symbol duration, p^ and p^(B) for each pair of said plurality of cells. A first cell of said each pair is considered as a reference cell and a second cell of said each pair is considered as an adjacent cell. p^w is used for scaling of transmit power of non-Cell-Specific Reference Signal "non-CRS" Resource Elements "REs" that are sent in symbols in which CRSs are not present, referred to as type A REs. p^(B) is used for scaling of transmit power of non- CRS REs that are sent in symbols including CRSs, referred to as type B REs. Both p^ and p^(B) scale transmit power compared to transmit power of REs carrying CRSs.

Moreover, the estimation node is configured for setting up a system of linear equations. The linear system relates load of the plurality of cells to the RSRP and the RS-SINR of the plurality of cells. Furthermore, the estimation node is configured for providing a respective value indicating load of each cell by solving the system of linear equations with respect to load.

According to further aspects, the object is achieved by a computer program and a computer program carrier corresponding to the aspects above.

Thanks to that PCI, RSTD, p^ and p^(B), i.e. values thereof, are used, an accurate modelling of the contribution of each adjacent cell to an overall interference is achieved, which in turn permits accurate estimation of the load of each measured cell.

According to the embodiments herein, the respective value of estimated load for each cell is obtained simultaneously when the system of linear equations is solved. In particular, the embodiments herein combine values indicating RS-SINR and RSRP while taking into account impact of PCI assignment to CRS pattern in addition to values of RSTD between cells, detected by the user equipment, or a drive test unit.

BRIEF DESCRIPTION OF THE DRAWINGS

The various aspects of embodiments disclosed herein, including particular features and advantages thereof, will be readily understood from the following detailed description and the accompanying drawings, in which:

Figure 1 is a schematic overview illustrating CRS pattern,

Figure 2a and Figure 2b are illustrations of collision between CRSs in two different cells,

Figure 3 is a schematic overview of exemplifying network(s) in which

embodiments herein may be implemented, Figure 4 is a flowchart illustrating embodiments of the method in the estimation node, and

Figure 5 is a block diagram illustrating embodiments of the estimation node.

DETAILED DESCRIPTION

Throughout the following description similar reference numerals have been used to denote similar features, such as nodes, actions, steps, modules, circuits, parts, items elements, units or the like, when applicable. In the Figures, features that appear in some embodiments are indicated by dashed lines.

Figure 3a to Figure 3c depict an exemplifying network 100 in which embodiments herein may be implemented. In this example, the network 100 is a Long Term Evolution (LTE).

In other examples, the network 100 may be any known or future OFDMA network. Parameters, obtained e.g. in action A010 below, may then be adapted to their equivalents in any such known or future network.

Commonly for Figure 3a to Figure 3c, cells 101 -103 are illustrated. The cells may be operated by the same or different base stations. Each cell 101 -103 is identified by its PCI. In each of the Figures 3a to Figure 3c attention is directed towards the entity that performs the method summarized in the summary section.

With reference to Figure 3a, the network 100 may be said to comprise a user equipment 1 10. This means that the user equipment 1 10 is present in the network 100. Accordingly, the method summarized in the summary section may be performed by the user equipment 1 10.

As used herein, the term "user equipment" may refer to a wireless

communication device, a machine-to-machine (M2M) device, a mobile phone, a cellular phone, a Personal Digital Assistant (PDA) equipped with radio communication capabilities, a smartphone, a laptop or personal computer (PC) equipped with an internal or external mobile broadband modem, a tablet PC with radio communication capabilities, a portable electronic radio communication device, a sensor device equipped with radio communication capabilities or the like. The sensor may be any kind of weather sensor, such as wind, temperature, air pressure, humidity etc. As further examples, the sensor may be a light sensor, an electronic or electric switch, a microphone, a loudspeaker, a camera sensor etc. The term "user" may indirectly refer to the wireless device.

Sometimes, the term "user" may be used to refer to the user equipment or the like as above. It shall be understood that the user may not necessarily involve a human user. The term "user" may also refer to a machine, a software component or the like using certain functions, methods and similar. With reference to Figure 3b, the network 100 may be said to comprise a radio network node 120, which may operate one or more of the cells 101 -103. Accordingly, the method summarized in the summary section may be performed by the radio network node 120. As used herein, the term "radio network node" may refer to an evolved Node B

(eNB), a control node controlling one or more Remote Radio Units (RRUs), an access point or the like.

With reference to Figure 3c, the network 100 may be said to comprise a node 130 implementing a planning tool, such as a NDO tool. The node 130 is denoted NDO tool node in the Figure. Accordingly, the method summarized in the summary section may be performed by the node 130 implementing the planning tool. In Figure 3c, a drive test unit 150 is further illustrated. The drive test unit 150 is a kind of user equipment with some additional functions for facilitating network design and optimization.

In Figure 3a to Figure 3c, an estimation node 140 is illustrated in order to simplify description of the embodiments herein. Consequently, the estimation node 140 may be the user equipment 1 10, the radio network node 120 or the node 130 implementing the planning tool according to various embodiments herein.

Moreover, in all of Figure 3a to Figure 3c, "Pi, Qi, ..." refer to values obtained by the estimation node 140 and "t/j" refers to load as explained in more detail with reference to Figure 4 below. Figure 4 illustrates an exemplifying method according to embodiments herein when implemented in the network(s) 100 of Figure 3. The estimation node 140 performs a method for estimating load on the plurality of cells 101-103 of a cellular network 100.

One or more of the following actions may be performed in any suitable order.

Action A010

The estimation node 140 obtains RSRP, RS-SINR, RSTD and PCI for said plurality of cells 101-103. In more detail, the estimation node 140 obtains a respective value indicating the RSRP, the RS-SINR, the RSTD and the PCI for each cell of the plurality of cells 101-103.

In some particular embodiments, referred to as "RSSI embodiments" below, the estimation node 140 may obtain RSSI for said plurality of cells 101-103, i.e. similar to the above a respective value indicating the RSSI for each cell of the plurality of cells 101 - 103.

In some examples, the estimation node 130 only obtains the RS-SINR of the serving cell, but not the RS-SINR of any other cell. The serving cell is the detected cell with the highest RSRP. To obtain only the RS-SINR is not desired, but may happen for various reasons. A problem is then that each sample provides just one equation for the system of linear equations below, which therefore isn't univocally solvable. Thus, it may be necessary to obtain a buffer of RS-SINR values, e.g. measured by the user equipment 110, until the system of equations becomes univocally solvable. In this context, the term "sample" refers to one or more measurements that are associated with a certain time instant. Accordingly, the sample implies a measurement of RSTD, RSRP, RS-SINR and/or RSSI for the plurality of cells in the certain time instant, such as a time period.

As mentioned above, the method may be performed by the user equipment 1 10, and wherein the obtaining A010 comprises measuring one or more of the RSRP, the RS- SINR, the RSTD, the PCI and the RSSI for said plurality of cells 101 -103.

As mentioned above, the method may be performed by the radio network node

120, and wherein the obtaining A010 comprises receiving one or more of the RSRP, the RS-SINR, the RSTD, the PCI and the RSSI for said plurality of cells 101 -103 from a user equipment 1 10.

Similarly, as mentioned above, the method may be performed by the node 130 implementing a planning tool, and wherein the obtaining A010 comprises receiving one or more of the RSRP, the RS-SINR, the RSTD, the PCI and the RSSI for said plurality of cells 101-103 from a drive-test unit. Action A020

As an example relating to the embodiment of Figure 3b and Figure 3c, the user equipment 110 or the drive test unit 150 may detect each of the plurality of cells 101 - 103, e.g. by demodulation of synchronization signals, such as Primary Synchronization Signal, Secondary Synchronization Signal and the like. The PCI may then be obtained in action A060 as described below.

Action A030

As an example relating to the embodiment of Figure 3a, the estimation node 140, i.e. the user equipment 1 10, may obtain the RSRP, by measurements according to known manners.

As an example relating to the embodiment of Figure 3b and Figure 3c, the estimation node 140 may receive the RSRP, i.e. values indicating RSRP, from the user equipment 1 10 or the drive test unit 150, which may have measured the RSRP according to known manners.

Action A040

As an example relating to the embodiment of Figure 3a, the estimation node 140, i.e. the user equipment 1 10, may obtain the RS-SINR, by measurements according to known manners.

As an example relating to the embodiment of Figure 3b and Figure 3c, the estimation node 140 may receive the RS-SINR, i.e. values indicating RS-SINR, from the user equipment 110 or the drive test unit 150, which may have measured the RS-SINR according to known manners.

Action A050

As an example relating to the embodiment of Figure 3a, the estimation node 140, i.e. the user equipment 1 10, may obtain the RSTD, by measurements according to known manners.

As an example relating to the embodiment of Figure 3b and Figure 3c, the estimation node 140 may receive the RSTD, i.e. values indicating RSTD, from the user equipment 1 10 or the drive test unit 150, which may have measured the RSTD according to known manners.

The RSTD between a reference cell and an adjacent cell may be measured on any downlink signal, such as CRSs, Positioning Reference Signals (PRSs) or the like.

Action A060

For example after action A020, the estimation node 140 may obtain the PCI , i.e. a respective value indicating PCI for each cell of the plurality of cells 101 -103. As an example, the PCI may be derived from the demodulated synchronization signals.

Action A070

The estimation node 140 may check if there are any further cells. If so, the estimation node 140 may proceed by performing action A010 for such any further cells that will be considered as included among the plurality of cells 101 -103.

If there are no further cells, the estimation node 140 may proceed by performing one or more of actions A090 through action A130.

Action A090

The estimation node 140 determines a respective alpha coefficient and a respective beta coefficient based on the PCI, the RSTD, a symbol duration, p^ and p^(B) (rho_A and rho_B) for each pair of said plurality of cells 101 -103. A first cell of said each pair is considered as a reference cell and a second cell of said each pair is considered as an adjacent cell, p^ is used for scaling of transmit power of non-Cell-Specific Reference Signal "non-CRS" Resource Elements "REs" that are sent in symbols in which CRSs are not present, referred to as type A REs. p^(B) is used for scaling of transmit power of non-CRS REs that are sent in symbols including CRSs, referred to as type B REs. Both pW and p^(B) scale transmit power compared to transmit power of REs carrying CRSs. The symbol duration is a network parameter, with two possible values related to normal and extended cyclic prefix. This network parameter can be obtained as known in the art.

In this manner, a type of collision between the CRSs of the reference cell and the adjacent cell is determined. The reference cell and the adjacent cell are selected from among the plurality of cells, i.e. the reference cell and the adjacent cell are taken in twos, or pairs, for each variation without repetition based on the obtained RSTD and PCI. In case the RSTD matches an integer number of symbols:

• If CRSs in the reference cell collide with CRSs in the adjacent cell, the

respective alpha coefficient is set to 0, while the respective beta coefficient is set to 1.

• If CRSs in the reference cell collide with non-CRS REs of type A in the

adjacent cell, the respective alpha coefficient is set to the value of p^w of the adjacent cell, while the respective beta coefficient is set to 0.

• If CRSs in the reference cell collide with non-CRS REs of type B in the

adjacent cell, the respective alpha coefficient is set to the value of p^(B) of the adjacent cell, while the respective beta coefficient is set to 0.

Otherwise, when the RSTD does not match an integer number of symbols, the coefficients would be calculated as a linear combination of the values from the previous case proportionally to the level of overlapping.

In more detail, the estimation node 130 may determine the respective alpha and beta coefficients by setting the respective alpha coefficient equal to <¾·, where

_TW

', (A) . ', (I!) where rjy* and riy* are overlapping times between CRSs in the i-th cell, being the reference cell, and type A REs or type B REs in the j-th cell, being the adjacent cell, within a time symbol τ window, and

are respectively the values of p^w and p^(B) in the j-th cell, and setting the respective beta coefficient equal to β^ , where

R. . = 1

ι,] _τ >

where is overlapping time between CRSs in the i-th cell and CRSs in the j-th cell within a time symbol τ window.

When action A010 is split into several actions A020 to A060 as above, the present action, i.e. action A090, may be performed before action A030, A040, but after action A050 and A060.

Action A100

The estimation node 140 sets up, or generates, a system of linear equations. The linear system relates load of the plurality of cells 101 -103 to the RSRP and the RS-SINR of the plurality of cells 101 -103.

The system of linear equations may comprise:

A^■ x = b, where

where is the RSRP of the i-th cell, t/j is the load of the i-th cell, Qi is the RS- SINR of the i-th cell, a _i is the alpha coefficient where the i-th cell is the reference cell and the j-th is the adjacent cell, is the beta coefficient where i-th cell is the reference cell and the j-th is the adjacent cell, N_T is the per-subcarrier thermal noise power, and N is the cardinality of the plurality of cells.

Each linear equation may express the RS-SINR associated with each cell as the RSRP of that cell divided by an average interference power plus thermal noise power.

The interference power is computed as a sum of the RSRP of each adjacent cell multiplied by the load weighted by the respective alpha coefficient plus the respective beta coefficient, where the load of each cell are the unknowns of the system of linear equations. In the RSSI embodiments mentioned above, the estimation node 140 further sets up the system of linear equations by including a further linear equation in the system of linear equations based on the obtained RSSI. The further linear equation further relates load of the plurality of cells 101 -103 to the RSSI . In this manner, redundancy may be achieved and/or compensation for nonlinearly independent equations due to collisions between CRSs may be obtained.

In some examples, parts of this action may be performed as soon as requisite information for the system of linear equations becomes available in action A010. This means that it may not always be necessary to perform this action completely after action A010. Expressed differently, the matrices A, x, b may be built up successively as information becomes available in action A010.

Action A1 10

Before proceeding to action A130, the estimation node 140 may check that the system of linear equations is univocally solvable before proceeding with the providing of the load.

When the system of linear equations is underdetermined, i.e. not univocally (non- univocally) solvable, the estimation node 140 may proceed with action A010 until the system of linear equations is univocally solvable or even overdetermined. In practice, this means that the system is undetermined if at least one pair of cells with colliding CRSs at the UE exists.

As is well-known, an overdetermined system includes a number of equations that is greater than a number of unknowns, whereas a system that is not univocally solvable includes fewer equations than number of unknowns. The overdetermined system is commonly solved by multivariable linear regression algorithms as is known in the art.

An advantage with an overdetermined system of linear equations is that robustness against potential noise in e.g. one or more of RSRP, RSTD, RS-SINR and RSSI is achieved.

Action A130

When the system of equations is univocally solvable or overdetermined, the estimation node 140 provides a respective value indicating load of each cell 101 , 102, 103 by solving the system of linear equations with respect to load.

Thus, the plurality of cells 101-103 a set of values indicating load is provided, where the set of values comprises the respective value indicating load for each cell 101 , 102, 103.

The set of values indicating load may be used by the user equipment 1 10 to anticipate network congestion issues and prevent from a potential service outage, or by the radio network node 120 to make radio resource management decisions, e.g. related to load balancing, handover, etc., without using the X2 interface. Alternatively or additionally, the embodiments herein may be adapted to estimate the cell load derived from drive-tests to be used by the node 130 implementing NDO tools for RF shaping, capacity dimensioning, network troubleshooting, etc. without the need of an Operation and Support System (OSS) infrastructure. The proposed embodiments may be implemented as a separate module with a common interface to different kinds of NDO tools, or the embodiments may be integrated in each of such tools.

As described above, an assumption according to the embodiments herein is that power in non-CRS REs is only transmitted when there is available data, i.e.

proportionally to the cell load.

To conclude, the following shall be noted in relation to at least some of the embodiments herein.

The consideration of the PCI value assigned to every detected cell, as well as the use of the RSTD between those cells enables more accurate estimation of cell load in e.g. LTE based on RF measurements.

Some embodiments herein allow for prediction of when a particular condition make it impossible to reach an accurate cell load estimation, i.e. CRSs of the reference cell do overlap with CRSs of adjacent cells. In these cases, the proposed embodiments may either inform about the uncertainty of the obtained RSRP and/or RS-SINR and/or RSTD, or - if possible - continuing to obtain new samples of these measures until the system of equations become univocally solvable.

The proposed embodiments make use of the RSTD to estimate the cell load without uncertainty when it is mathematically possible, i.e. CRSs of the reference cell do overlap only with non-CRS REs of adjacent cells, and hence the interference depends on the cell load.

The proposed embodiments make use of information that, according to 3GPP, may be available at the estimation node, such as the user equipment 1 10. New standards would therefore not be required in order to implement the embodiments herein.

Next, a detailed description on how to obtain and solve the system of linear equations is provided. Subsequently, it is described how to obtain the load estimation, i.e. the respective value indicating load, for each detected cell. According to 3GPP the user equipment 1 10 shall be able to continuously perform RSRP and RS-SINR measurements of identified intra- and inter-frequency cells during the Radio Resource Control (RRC) connected-mode stage. This information is necessary, for instance, for handover purposes or channel quality estimation. It is worth highlighting that both RSRP and RS-SINR values are not instantaneous measurements but the UE evaluates them over several symbols, and reports an average over such period of time (usually 100 ms). Therefore, the contribution of an adjacent cell to the overall interference depends on the actual average load, which is a key assumption in this invention. On the other hand, RSTD measurements can be performed on PRS (as for location-based services) or on any other downlink signal, such as CRS, while PCI values are obtained after decoding the synchronization signals. Let us consider a UE that performs the following set of RSRP measurements:

[Pi Pi (1 ) where P_t is the RSRP from the /-th cell and N is the number of detected cells. Therefore the RS-SINR (in linear units) of the /-th cell (i.e. reference cell) associated with that set of RSRP measurements can be written as:

where P_t is the RSRP from the /-th cell, l_iti is the average interference power from the y^'-th cell (i.e. adjacent cell) on the REs of the /-th cell carrying CRSs, N_T is the per- subcarrier thermal noise power. In OFDM the own cell interference is assumed to be negligible, that is why the contribution of the /-th cell is not counted in the overall interference.

The average contribution of an adjacent cell can be modeled just as a linear proportion of its RSRP. Such a proportion mainly depends on the cell load, but also on the PCI plan, the power settings, and the synchronization level between cells. Therefore, the average interference power from the y^'-th cell on the REs of the /-th cell carrying CRSs can be generalized as:

(3)

I _j = P_j ^■ (a_u ^■ U_j + where U_j ε [0,1] is the cell load of the y^'-th cell, and <¾· and are referred to as the first and second coefficients respectively, which relate the RSRP and their actual contribution to the overall interference depending on the configuration of the /^'-th and y^'-th cell respectively. The actual values of the aforementioned coefficients depend on the type of collision, which can be derived from the RSTD measurements and the PCI assignment. <¾· can be defined as the ratio of interference power from non-CRS REs to the RSRP power from the y^'-th cell experienced when measuring the RS-SINR from the /- th cell. can be defined as the ratio of interference power from CRS REs to the RSRP power of the y^'-th cell experienced when measuring the RS-SINR from the /^'-th cell.

Table 1 : Values of <¾· and depending on type of collision between the s-th and /-th cells. Table 1 summarizes the values of <¾· and for the case of a time-difference that matches an integer number of symbols. Otherwise, the coefficients would be calculated as a linear combination of the values in Table 1 proportionally to the level of overlapping. Eq. 4 shows that <¾· is computed as the proportion of time in which the measured CRS RE from the /^'-th cell collides with every type of non-CRS REs from the y- the cell multiplied by their power scaling factors (i.e.

Eq. 5 shows that is computed as the proportion of time in which the measured CRS RE from the /^'-th cell collides with the CRS RE from the y^'-th cell.

, (B)

(A) .

+^■ ^' L„ ^(β)

ai = τ ^■p_j (4) (CRS)

βυ =

(5) where τ> is the overlapping time between CRS REs in the /-th cell and non-

CRS REs of type A in the y^'-th cell, τ[^Β is the overlapping time between CRS REs in the /- th cell and non-CRS REs of type B in the y^'-th cell, is the overlapping time between CRS REs in the /-th cell and CRS REs in the y^'-th cell, and τ is the symbol duration in the /^'-th cell, where τ = + + T^^RS) .

By replacing l_iti from eq. 3 in eq. 2, the following expression is obtained:

(6) j=l,j≠i ¹ j=i,j≠i

which linearly relates the cell load of the adjacent cells with the RSRP and the RS-SINR. In that case, the previous equation can be expressed in a matrix form as:

A - x = b (7) where A is the design matrix, b is the set of experimental measurements, and x is the set of unknowns, which are defined as:

The matrix expression shown in eq. 7 consists of a system of N linearly independent equations, which can be solved as: as long as the reception of CRSs between the reference cell and any of its adjacent cells do not collide, which can be formulated as:

(12) ai_j≠ 0 V£,; G [1 N], i≠j

Otherwise, it would be necessary to buffer enough samples, so that there exist at least the same amount of linearly independent equations and variables, i.e. detected cells. This can be verified, for instance, by calculating the rank of matrix A.

With reference to Figure 5, a schematic block diagram of embodiments of the estimation node 140 of Figure 3 is shown.

The estimation node 140 may comprise a processing module 501 , such as a means for performing the methods described herein. The means may be embodied in the form of one or more hardware modules and/or one or more software modules.

The estimation node 140 may further comprise a memory 502. The memory may comprise, such as contain or store, instructions, e.g. in the form of a computer program 503, which may comprise computer readable code units.

According to some embodiments herein, the estimation node 140 and/or the processing module 501 comprises a processing circuit 504 as an exemplifying hardware module. Accordingly, the processing module 501 may be embodied in the form of, or 'realized by', the processing circuit 504. The instructions may be executable by the processing circuit 504, whereby the estimation node 140 is operative to perform the methods of Figure 4. As another example, the instructions, when executed by the estimation node 140 and/or the processing circuit 504, may cause the estimation node 140 to perform the method according to Figure 4.

In view of the above, in one example, there is provided an estimation node 140 for estimating load on a plurality of cells 101-103. Again, the memory 502 contains the instructions executable by said processing circuit 504 whereby said estimation node 140 is operative for:

obtaining RSRP, RS-SINR, RSTD and PCI for said plurality of cells 101-103, determining a respective alpha coefficient and a respective beta coefficient based on the PCI, the RSTD, a symbol duration, and p^(B) for each pair of said plurality of cells 101-103, wherein a first cell of said each pair is considered as a reference cell and a second cell of said each pair is considered as an adjacent cell, wherein p^> is used for scaling of transmit power of non-Cell-Specific Reference Signal "non-CRS" Resource Elements "REs" that are sent in symbols in which CRSs are not present, referred to as type A REs, and p^(B) is used for scaling of transmit power of non-CRS REs that are sent in symbols including CRSs, referred to as type B REs, wherein both p^ and p^(B) scale transmit power compared to transmit power of REs carrying CRSs,

setting up a system of linear equations, wherein the linear system relates load of the plurality of cells 101-103 to the RSRP and the RS-SINR of the plurality of cells 101- 103, and

providing a respective value indicating load of each cell 101 , 102, 103 by solving the system of linear equations with respect to load.

Figure 5 further illustrates a carrier 505, or program carrier, which comprises the computer program 503 as described directly above. In some embodiments, the processing module 501 comprises an Input/Output module 506, which may be exemplified by a receiving module and/or a sending module as described below when applicable.

In further embodiments, the estimation node 140 and/or the processing module 501 may comprise one or more of an obtaining module 510, a determining module 520, a setting up module 530, a providing module 540, a setting module 550, a checking module 560, a measuring module 570, and a receiving module 580 as exemplifying hardware modules. In other examples, one or more of the aforementioned exemplifying hardware modules may be implemented as one or more software modules.

Accordingly, the estimation node 140 is configured for estimating load on a plurality of cells 101-103 of a cellular network 100.

Therefore, according to the various embodiments described above, the estimation node 140 and/or the processing module 501 and/or the obtaining module 510 is configured for obtaining RSRP, RS-SINR, RSTD and PCI for said plurality of cells 101- 103.

The estimation node 140 and/or the processing module 501 and/or the determining module 520 is configured for determining a respective alpha coefficient and a respective beta coefficient based on the PCI, the RSTD, a symbol duration, p^ and for each pair of said plurality of cells 101 -103. A first cell of said each pair is considered as a reference cell and a second cell of said each pair is considered as an adjacent cell, is used for scaling of transmit power of non-Cell-Specific Reference Signal "non-CRS" Resource Elements "REs" that are sent in symbols in which CRSs are not present, referred to as type A REs, and is used for scaling of transmit power of non-CRS REs that are sent in symbols including CRSs, referred to as type B REs. Both and scale transmit power compared to transmit power of REs carrying CRSs.

Furthermore, the estimation node 140 and/or the processing module 501 and/or the setting up module 530 is configured for setting up a system of linear equations. The linear system relates load of the plurality of cells 101 -103 to the RSRP and the RS-SINR of the plurality of cells 101-103.

Moreover, the estimation node 140 and/or the processing module 501 and/or the providing module 540 is configured for providing a respective value indicating load of each cell 101 , 102, 103 by solving the system of linear equations with respect to load.

In some embodiments, the estimation node 140 and/or the processing module 501 and/or the setting module 550 is configured for setting the respective alpha coefficient equal to <¾·, where

where τ> and rjy are overlapping times between CRSs in the i-th cell, being the reference cell, and type A REs or type B REs in the j-th cell, being the adjacent cell, within a time symbol τ window, and are respectively the values of and in the j-th cell, and

setting the respective beta coefficient equal to β^, where

where τ> . is overlapping time between CRSs in the i-th cell and CRSs in the j-th cell within a time symbol τ window.

The system of linear equations may comprise:

A^■ x = b, where

where Pj is the RSRP of the i-th cell, ί/; is the load of the i-th cell, Qi is the RS- SINR of the i-th cell, a_itj is the alpha coefficient where the i-th cell is the reference cell and the j-th is the adjacent cell, is the beta coefficient where i-th cell is the reference cell and the j-th is the adjacent cell, N_T is the per-subcarrier thermal noise power, and N is the cardinality of the plurality of cells.

In some embodiments, the estimation node 140 and/or the processing module 501 and/or the obtaining module 510, or a further obtaining module (not shown), is configured for obtaining by further obtaining RSSI for said plurality of cells 101 -103, and wherein the estimation node 140 and/or the processing module 501 and/or the setting up module 520, or a further setting up module (not shown), is further configured for setting up by including a further linear equation in the system of linear equations based on the obtained RSSI. The further linear equation further relates load of the plurality of cells 101 -103 to the RSSI.

In some embodiments, the estimation node 140 and/or the processing module 501 and/or the checking module 560 is configured for checking that the system of linear equations is univocally solvable before proceeding with the providing of the load, and wherein the estimation node 140 and/or the processing module 501 and/or a proceeding module (not shown) is configured for proceeding with the obtaining until the system of linear equations is univocally solvable or overdetermined, when the system of linear equations is underdetermined. The estimation node 140 may be the user equipment 1 10, and wherein the user equipment 1 10 and/or the processing module 501 and/or the measuring module 570 is configured for measuring one or more of the RSRP, the RS-SINR, the RSTD, the PCI and the RSSI for said plurality of cells 101-103.

The estimation node 140 may be the radio network node 120, and wherein the radio network node 120 and/or the processing module 501 and/or the receiving module 580 is configured for receiving one or more of the RSRP, the RS-SINR, the RSTD, the PCI and the RSSI for said plurality of cells 101-103 from the user equipment 1 10.

The estimation node 140 may be the node 130 implementing a planning tool, and wherein the node 130 and/or the processing module 501 and/or the receiving module 580 is configured for receiving one or more of the RSRP, the RS-SINR, the RSTD, the PCI and the RSSI for said plurality of cells 101-103 from a drive-test unit.

As used herein, the term "node", or "network node", may refer to one or more physical entities, such as devices, apparatuses, computers, servers or the like. This may mean that embodiments herein may be implemented in one physical entity. Alternatively, the embodiments herein may be implemented in a plurality of physical entities, such as an arrangement comprising said one or more physical entities, i.e. the embodiments may be implemented in a distributed manner, such as on a set of server machines of a cloud based system.

As used herein, the term "module" may refer to one or more functional modules, each of which may be implemented as one or more hardware modules and/or one or more software modules and/or a combined software/hardware module in a node. In some examples, the module may represent a functional unit realized as software and/or hardware of the node.

As used herein, the term "computer program carrier", "program carrier", or

"carrier", may refer to one of an electronic signal, an optical signal, a radio signal, and a computer readable medium. In some examples, the computer program carrier may exclude transitory, propagating signals, such as the electronic, optical and/or radio signal. Thus, in these examples, the computer program carrier may be a non-transitory carrier, such as a non-transitory computer readable medium. As used herein, the term "processing module" may include one or more hardware modules, one or more software modules or a combination thereof. Any such module, be it a hardware, software or a combined hardware-software module, may be a determining means, estimating means, capturing means, associating means, comparing means, identification means, selecting means, receiving means, sending means or the like as disclosed herein. As an example, the expression "means" may comprise a module corresponding for example to the modules listed above in conjunction with the Figures.

As used herein, the term "software module" may refer to a software application, a Dynamic Link Library (DLL), a software component, a software object, an object according to Component Object Model (COM), a software component, a software function, a software engine, an executable binary software file or the like.

As used herein, the terms "processing module" and "processing circuit" encompass, for example: a processing unit comprising e.g. one or more processors, an Application Specific integrated Circuit (ASIC), a Field-Programmable Gate Array (FPGA) or the like. The processing circuit or the like may comprise one or more processor kernels.

As used herein, the expression "configured to/for" may mean that a processing circuit is configured to, such as adapted to or operative to, by means of software configuration and/or hardware configuration, perform one or more of the actions described herein.

As used herein, the term "action" may refer to an action, a step, an operation, a response, a reaction, an activity or the like. It shall be noted that an action herein may be split into two or more sub-actions as applicable. Moreover, also as applicable, it shall be noted that two or more of the actions described herein may be merged into a single action.

As used herein, the term "memory" may refer to a hard disk, a magnetic storage medium, a portable computer diskette or disc, flash memory, random access memory (RAM) or the like. Furthermore, the term "memory" may refer to an internal register memory of a processor or the like.

As used herein, the term "computer readable medium" may be a Universal Serial

Bus (USB) memory, a DVD-disc, a Blu-ray disc, a software module that is received as a stream of data, a Flash memory, a hard drive, a memory card, such as a MemoryStick, a Multimedia Card (MMC), Secure Digital (SD) card, etc. One or more of the aforementioned examples of computer readable medium may be provided as one or more computer program products.

As used herein, the term "computer readable code units" may be text of a computer program, parts of or an entire binary file representing a computer program in a compiled format or anything there between.

As used herein, the expression "transmit" and "send" are considered to be interchangeable. These expressions include transmission by broadcasting, uni-casting, group-casting and the like. In this context, a transmission by broadcasting may be received and decoded by any authorized device within range. In case of uni-casting, one specifically addressed device may receive and decode the transmission. In case of group-casting, a group of specifically addressed devices may receive and decode the transmission.

As used herein, the terms "number" and/or "value" may be any kind of digit, such as binary, real, imaginary or rational number or the like. Moreover, "number" and/or "value" may be one or more characters, such as a letter or a string of letters. "Number" and/or "value" may also be represented by a string of bits, i.e. zeros and/or ones.

As used herein, the term "set of may refer to one or more of something. E.g. a set of devices may refer to one or more devices, a set of parameters may refer to one or more parameters or the like according to the embodiments herein.

As used herein, the expression "in some embodiments" has been used to indicate that the features of the embodiment described may be combined with any other embodiment disclosed herein.

Further, as used herein, the common abbreviation "e.g.", which derives from the Latin phrase "exempli gratia," may be used to introduce or specify a general example or examples of a previously mentioned item, and is not intended to be limiting of such item. If used herein, the common abbreviation "i.e.", which derives from the Latin phrase "id est," may be used to specify a particular item from a more general recitation. The common abbreviation "etc.", which derives from the Latin expression "et cetera" meaning "and other things" or "and so on" may have been used herein to indicate that further features, similar to the ones that have just been enumerated, exist.

Even though embodiments of the various aspects have been described, many different alterations, modifications and the like thereof will become apparent for those skilled in the art. The described embodiments are therefore not intended to limit the scope of the present disclosure.

Claims

1. A method for estimating load on a plurality of cells (101 -103) of a cellular network (100), wherein the method comprises:

obtaining (A010) Reference-Signal-Received-Power "RSRP", Reference- Signal-Signal-To-lnterference-and-Noise-Ratio "RS-SINR", Reference-Signal-Time- Difference "RSTD", and Physical Cell Identity "PCI" for said plurality of cells (101 - 103),

determining (A090) a respective alpha coefficient and a respective beta coefficient based on the PCI, the RSTD, a symbol duration, p^ and p^(B) for each pair of said plurality of cells (101 -103), wherein a first cell of said each pair is considered as a reference cell and a second cell of said each pair is considered as an adjacent cell, wherein p^ is used for scaling of transmit power of non-Cell- Specific Reference Signal "non-CRS" Resource Elements "REs" that are sent in symbols in which CRSs are not present, referred to as type A REs, and p^(B) is used for scaling of transmit power of non-CRS REs that are sent in symbols including CRSs, referred to as type B REs, wherein both p^ and p^(B) scale transmit power compared to transmit power of REs carrying CRSs,

setting up (A100) a system of linear equations, wherein the linear system relates load of the plurality of cells (101 -103) to the RSRP and the RS-SINR of the plurality of cells (101-103), and

providing (A130) a respective value indicating load of each cell (101 , 102, 103) by solving the system of linear equations with respect to load.

2. The method according to claim 1 , wherein the determining (A090) of the respective alpha and beta coefficients comprises setting the respective alpha coefficient equal to ccij , where

Λ) (F)

' / / (A) . ', (I! ) where rjy* and τ[^Β are overlapping times between CRSs in the i-th cell, being the reference cell, and type A REs or type B REs in the j-th cell, being the adjacent cell, within a time symbol τ window, p^ and p ^B) are respectively the values of p^ and p^(B) in the j-th cell, and setting the respective beta coefficient equal to , , where

.(CBS)

— ^l'J where τ> . is overlapping time between CRSs in the i-th cell and CRSs in the cell within a time symbol τ window.

The method according to claim 1 or 2, wherein the system of linear equations comprises:

A ^■ x = b, where

where P_; is the RSRP of the i-th cell, U_t is the load of the i-th cell, Q_t is the RS-SINR of the i-th cell, is the alpha coefficient where the i-th cell is the reference cell and the j-th is the adjacent cell, is the beta coefficient where i-th cell is the reference cell and the j-th is the adjacent cell, N_T is the per-subcarrier thermal noise power, and N is the cardinality of the plurality of cells.

4. The method according to any one of claims 1 -3, wherein the obtaining (A010) further comprises obtaining Reference Signal Strength Indicator "RSSI" for said plurality of cells (101 -103), and wherein the setting up (A100) comprises including a further linear equation in the system of linear equations based on the obtained RSSI, wherein the further linear equation further relates load of the plurality of cells (101 - 103) to the RSSI.

5. The method according to any one of claim 1-4, wherein the method comprises:

checking (A1 10) that the system of linear equations is univocally solvable before proceeding with the providing of the load, and

when the system of linear equations is underdetermined proceeding with the obtaining (A010) until the system of linear equations is univocally solvable or overdetermined.

6. The method according to any one of claims 1 -5, wherein the method is performed by a user equipment (1 10), and wherein the obtaining (A010) comprises measuring one or more of the RSRP, the RS-SINR, the RSTD, the PCI and the RSSI for said plurality of cells (101-103).

7. The method according to any one of claims 1 -5, wherein the method is performed by a radio network node (120), and wherein the obtaining (A010) comprises receiving one or more of the RSRP, the RS-SINR, the RSTD, the PCI and the RSSI for said plurality of cells (101-103) from a user equipment (1 10).

8. The method according to any one of claims 1 -5, wherein the method is performed by a node (130) implementing a planning tool, and wherein the obtaining (A010) comprises receiving one or more of the RSRP, the RS-SINR, the RSTD, the PCI and the RSSI for said plurality of cells (101-103) from a drive-test unit.

9. A computer program (503), comprising computer readable code units which when executed on an estimation node (140) causes the estimation node (140) to perform the method according to any one of claims 1-8. 10. The computer program (503) according to claim 9, wherein the estimation node (140) is a user equipment (1 10), a radio network node (120) or a node (130) implementing a planning tool.

1 1 . A carrier (505) comprising the computer program (503) according to claim 9 or 10, wherein the carrier (505) is one of an electronic signal, an optical signal, a radio signal and a computer readable medium.

12. An estimation node (140) configured for estimating load on a plurality of cells (101 - 103) of a cellular network (100), wherein the estimation node (140) is configured for: obtaining Reference-Signal-Received-Power "RSRP", Reference-Signal- Signal-To-lnterference-and-Noise-Ratio "RS-SINR", Reference-Signal-Time- Difference "RSTD", and Physical Cell Identity "PCI" for said plurality of cells (101 - 103),

determining a respective alpha coefficient and a respective beta coefficient based on the PCI, the RSTD, a symbol duration, and for each pair of said plurality of cells (101-103), wherein a first cell of said each pair is considered as a reference cell and a second cell of said each pair is considered as an adjacent cell, wherein is used for scaling of transmit power of non-Cell-Specific Reference Signal "non-CRS" Resource Elements "REs" that are sent in symbols in which CRSs are not present, referred to as type A REs, and is used for scaling of transmit power of non-CRS REs that are sent in symbols including CRSs, referred to as type B REs, wherein both and scale transmit power compared to transmit power of REs carrying CRSs,

setting up a system of linear equations, wherein the linear system relates load of the plurality of cells (101-103) to the RSRP and the RS-SINR of the plurality of cells (101-103), and

providing a respective value indicating load of each cell (101 , 102, 103) by solving the system of linear equations with respect to load. 13. The estimation node (140) according to claim 12, wherein the estimation node (140) is configured for determining the respective alpha and beta coefficients by setting the respective alpha coefficient equal to <¾, where

Λ)

'/ / (A) . ', (I!) where rjy* and τ[^Β are overlapping times between CRSs in the i-th cell, being the reference cell, and type A REs or type B REs in the j-th cell, being the adjacent cell, within a time symbol τ window, p^ and are respectively the values of and in the j-th cell, and setting the respective beta coefficient equal to , where

14. The estimation node (140) according to claim 12 or 13, wherein the system of linear equations comprises:

A^■ x = b, where

where is the RSRP of the i-th cell, t/j is the load of the i-th cell, Qi is the RS-SINR of the i-th cell, (¾ is the alpha coefficient where the i-th cell is the reference cell and the j-th is the adjacent cell, is the beta coefficient where i-th cell is the reference cell and the j-th is the adjacent cell, N_T is the per-subcarrier thermal noise power, and N is the cardinality of the plurality of cells.

15. The estimation node (140) according to any one of claims 12-14, wherein the

estimation node (140) is configured for obtaining by further obtaining Reference

Signal Strength Indicator "RSSI" for said plurality of cells (101 -103), and wherein the estimation node (140) is configured for setting up by including a further linear equation in the system of linear equations based on the obtained RSSI, wherein the further linear equation further relates load of the plurality of cells (101 -103) to the RSSI.

16. The estimation node (140) according to any one of claim 12-15, wherein the

estimation node (140) is configured for checking that the system of linear equations is univocally solvable before proceeding with the providing of the load, and wherein the estimation node (140) is configured for proceeding with the obtaining until the system of linear equations is univocally solvable or overdetermined, when the system of linear equations is underdetermined.

17. The estimation node (140) according to any one of claims 12-16, wherein the estimation node (140) is a user equipment (1 10), and wherein the user equipment (1 10) is configured for obtaining by measuring one or more of the RSRP, the RS- SINR, the RSTD, the PCI and the RSSI for said plurality of cells (101 -103).

18. The estimation node (140) according to any one of claims 12-16, wherein the

estimation node (140) is a radio network node (120), and wherein the radio network node (120) is configured for obtaining by receiving one or more of the RSRP, the RS- SINR, the RSTD, the PCI and the RSSI for said plurality of cells (101 -103) from a user equipment (1 10).

19. The estimation node (140) according to any one of claims 12-16, wherein the

estimation node (140) is a node (130) implementing a planning tool, and wherein the node (130) is configured for obtaining by receiving one or more of the RSRP, the RS- SINR, the RSTD, the PCI and the RSSI for said plurality of cells (101 -103) from a drive-test unit.