WO2017220157A1

WO2017220157A1 - Estimation device, and method thereof

Info

Publication number: WO2017220157A1
Application number: PCT/EP2016/064606
Authority: WO
Inventors: Junshi Chen; Peter Almers; Chaitanya TUMULA
Original assignee: Huawei Technologies Co., Ltd.
Priority date: 2016-06-23
Filing date: 2016-06-23
Publication date: 2017-12-28

Abstract

The present invention relates to an estimation device (100) comprising a processor (102) configured to obtain a communication signal (y) comprising a plurality of resource elements (REs), the communication signal (y) carrying at least one first reference signal (RS1) of a serving cell (502) and at least one second reference signal (RS2) of at least one interfering cell (504), compute a first reconstructed reference signal for the serving cell (502), compute a second reconstructed reference signal for the interfering cell (504), provide a cancelled communication signal (y') based on the communication signal (y), the first reconstructed reference signal and the second reconstructed reference signal, compute a first noise power for a first resource element (RE0) of the plurality of the resource elements (REs) based on the cancelled communication signal (y'), compute a second noise power for a second resource element (RE1) of the plurality of resource elements (REs) based on the cancelled communication signal (y'), compute a noise power estimation (Z) based on the first noise power and the second noise power. Furthermore, the present invention also relates to a user device, corresponding methods, a computer program, and a computer program product.

Description

ESTIMATION DEVICE, AND METHOD THEREOF

Technical Field

The present invention relates to an estimation device. Furthermore, the present invention also relates to a user device comprising such an estimation device, a corresponding method, a computer program, and a computer program product.

Background

In Long Term Evolution (LTE) and in LTE-Advanced (LTE-A) system, the Physical Downlink Control Channel (PDCCH) is used to convey critical information about downlink/uplink scheduling assignments as well as power control commands to the User Equipment (UE). If the UE cannot demodulate PDCCH correctly, then the UE cannot get any PDSCH information as well. The Common Reference Signal (CRS) is used to estimate the channel response for detecting the PDCCH.

At the cell edge of a serving cell, the PDCCH channel is interfered by neighboring cell's PDCCH channel(s) with unknown probability, because the information about the distribution of neighboring cell's PDCCH is hard to know. Furthermore, the power of the serving cell^'s PDCCH and the neighboring cell's PDCCH are transparent to the UE, which makes the PDCCH detection more difficult, since traditional algorithms, such as MMSE or Symbol Level Interference Cancellation (SLIC), are based on the assumption that the power of the serving cell and the power of the neighboring cell are known.

In a conventional solution an algorithm is suggested which provides more robust PDCCH link level performance in scenarios with power ambiguity of the serving cell and the interfering cell. The algorithm is called enhanced Symbol Level Interference Cancellation (eSLIC), which takes explicit consideration of the unknown PDCCH power control parameters at both the serving cell and the neighboring cells. However, for the conventional solution to work well pure noise power of the received signal has to be known, which is difficult to obtain in many scenarios.

Summary

An objective of embodiments of the present invention is to provide a solution which mitigates or solves the drawbacks and problems of conventional solutions. An "or" in this description and the corresponding claims is to be understood as a mathematical OR which covers "and" and "or", and is not to be understand as an XOR (exclusive OR). The indefinite article "a" in this disclosure and claims is not limited to "one" and can also be understood as "one or more", i.e., plural.

The above objectives are solved by the subject matter of the independent claims. Further advantageous implementation forms of the present invention can be found in the dependent claims.

According to a first aspect of the invention, the above mentioned and other objectives are achieved with an estimation device comprising a processor configured to

obtain a communication signal comprising a plurality of resource elements, the communication signal carrying at least one first reference signal of a serving cell and at least one second reference signal of at least one interfering cell,

compute a first reconstructed reference signal for the serving cell,

compute a second reconstructed reference signal for the interfering cell,

provide a cancelled communication signal based on the communication signal, the first reconstructed reference signal and the second reconstructed reference signal,

compute a first noise power for a first resource element of the plurality of the resource elements based on the cancelled communication signal,

compute a second noise power for a second resource element of the plurality of resource elements based on the cancelled communication signal,

compute a noise power estimation based on the first noise power and the second noise power.

The estimation device according to the first aspect can estimate the noise power more accurately than conventional solutions. Further, the proposed solution can solve the problem of noise estimation in control signals (such as for PDCCH in LTE) when the reference signals (such as CRS) of the serving cell is not colliding with that of the interfering cell (i.e. non-colliding case), because the estimation device according to the first aspect is neither sensitive to the power ambiguity of the serving cell and the interfering cell, nor sensitive to the existence of control signals of the serving cell and the interfering cell in the communication signal. In a first possible implementation form of the estimation device according to the first aspect, the processor is configured to compute the noise power estimation based on a sum the first noise power and the second noise power. The first implementation form can provide an improved noise power estimation.

In a second possible implementation form of the estimation device according to the first implementation form of the first aspect, the processor is configured to

compute at least one third noise power for a third resource element among the plurality of resource elements, the third resource element being different from the first resource element and the second resource element,

compute the noise power estimation based on subtracting the third noise power from the sum of the first noise power and second noise power. The second implementation form can remove the influence of control signals in the communication signal, and thereby only keep the noise power to be estimated. Therefore, improved noise power estimation is provided.

In a third possible implementation form of the estimation device according to the second implementation form of the first aspect, no reference signal is mapped on the third resource element.

The third implementation form takes the advantage of the fact that the third resource element contains the same control signal as that of first two resource elements. Thereby, an improved noise power estimation is provided.

In a fourth possible implementation form of the estimation device according to the second or third implementation form of the first aspect, the processor is configured to compute the noise power estimation based on averaging the noise power estimation over the whole system bandwidth.

The system bandwidth is e.g. the bandwidth that one LTE signal is occupying, which is defined in 3GPP standards. For example, the bandwidth may be 1.4M, 3M, 5M, 10M, 15M, 20M, etc. The fourth implementation form averages the noise and remaining interference over the whole bandwidth, and thereby provides an improved noise power estimation. In a fifth possible implementation form of the estimation device according to the fourth implementation form of the first aspect, the processor is configured to compute the noise power estimation based on filtering the averaged noise power estimation over at least two subframes. A subframe is a unit defined by the system which means that subframes for different systems may differ from each other. For example, in 3GPP systems 1 subframe has a duration of 1 ms, which contains 14 symbols for normal Cyclic Prefix (CP) and 12 symbols for extended CP. The definitions for CPs and symbols are given by system standards. The fifth implementation form makes the noise estimation more stable and accurate by filtering the noise between at least two subframes which may be continuous.

In a sixth possible implementation form of the estimation device according to any of the preceding implementation forms of the first aspect or to the first aspect as such, the processor is configured to compute the first reconstructed reference signal and the second reconstructed reference signal based on

estimating a first channel response for the serving cell and a second channel response for the interfering cell,

multiplying the first channel response with the first reference signal so as to provide the first reconstructed reference signal,

multiplying the second channel response with the second reference signal so as to provide the second reconstructed reference signal.

The sixth implementation form can reconstruct the first and the second reference signals more accurately by using the first and second channel responses, respectively.

In a seventh possible implementation form of the estimation device according to the sixth implementation form of the first aspect, the processor is configured to provide the cancelled communication signal based on subtracting the first reconstructed reference signal and the second reconstructed reference signal from the communication signal.

The seventh implementation form can completely remove the first and the second reference signals from the communication signal which will result in improved noise power estimations. In an eight possible implementation form of the estimation device according to the seventh implementation form of the first aspect, the power of the cancelled communication signal is a product of the cancelled communication signal with its conjugation. In a ninth possible implementation form of the estimation device according to any of the preceding implementation forms of the first aspect or to the first aspect as such, the first reference signal is mapped on at least one first resource element and the second reference signal is mapped on at least one second resource element different from the first resource element.

According to a second aspect of the invention, the above mentioned and other objectives are achieved with user device for a cellular communication system, the user device comprising an estimation device according to any of the preceding claims,

a receiver configured to

receive a wireless communication signal corresponding to the communication signal.

In a first possible implementation form of the user device according to the second aspect, the cellular communication system is an OFDM system.

In a second possible implementation form of the user device according to the first implementation form of the second aspect, wherein the first reference signal and the second reference signal are Common Reference Signals, CRSs.

According to a third aspect of the invention, the above mentioned and other objectives are achieved with a method comprising

obtaining a communication signal comprising a plurality of resource elements, the communication signal carrying at least one first reference signal of a serving cell and at least one second reference signal of at least one interfering cell,

computing a first reconstructed reference signal for the serving cell,

computing a second reconstructed reference signal for the interfering cell,

providing a cancelled communication signal based on the communication signal, the first reconstructed reference signal and the second reconstructed reference signal,

computing a first noise power for a first resource element of the plurality of the resource elements based on the cancelled communication signal,

computing a second noise power for a second resource element of the plurality of the resource elements based on the cancelled communication signal,

computing a noise power estimation based on the first noise power and the second noise power. In a first possible implementation form of the method according to the third aspect, the method comprises

computing the noise power estimation based on a sum the first noise power and the second noise power.

In a second possible implementation form of the method according to the first implementation form of the third aspect, the method comprises

computing at least one third noise power for a third resource element among the plurality of resource elements, the third resource element being different from the first resource element and the second resource element,

computing the noise power estimation based on subtracting the third noise power from the sum of the first noise power and the second noise power.

In a third possible implementation form of the method according to the second implementation form of the third aspect, no reference signal is mapped on the third resource element.

In a fourth possible implementation form of the method according to the second or third implementation form of the third aspect, the method comprises

computing the averaged noise power estimation based on averaging the noise power estimation over the whole system bandwidth.

In a fifth possible implementation form of the method according to the fourth implementation form of the third aspect, the method comprises

computing the noise power estimation based on filtering the averaged noise power estimation over at least two subframes.

In a sixth possible implementation form of the method according to any of the preceding implementation forms of the third aspect or to the third aspect as such, the method comprises computing the first reconstructed reference signal and the second reconstructed reference signal based on estimating a first channel response for the serving cell and a second channel response for the interfering cell,

multiplying the second channel response with the second reference signal so as to provide the second reconstructed reference signal. In a seventh possible implementation form of the method according to the sixth implementation form of the third aspect, the method comprises

providing the cancelled communication signal based on subtracting the first reconstructed reference signal and the second reconstructed reference signal from the communication signal.

In an eight possible implementation form of the method according to the seventh implementation form of the third aspect, the power of the cancelled communication signal is a product of the cancelled communication signal with its conjugation.

In a ninth possible implementation form of the method according to any of the preceding implementation forms of the third aspect or to the third aspect as such, the first reference signal is mapped on at least one first resource element and the second reference signal is mapped on at least one second resource element different from the first resource element.

In a tenth possible implementation form of the method according to any of the preceding implementation forms of the third aspect or to the third aspect as such, the method further comprises

receiving a wireless communication signal corresponding to the communication signal.

The wireless communication signal may be received in a cellular communication system, such as an OFDM system.

In an eleventh possible implementation form of the method according to any of the preceding implementation forms of the third aspect or to the third aspect as such, the first reference signal and the second reference signal are Common Reference Signals, CRSs.

The advantages of the method according to the third aspect is the same as those for the corresponding estimation device according to the first aspect or to the user device according to the second aspect.

Embodiments of the present invention also relates to a computer program, characterized in code means, which when run by processing means causes said processing means to execute any method according to the present invention. Further, the invention also relates to a computer program product comprising a computer readable medium and said mentioned computer program, wherein said computer program is included in the computer readable medium, and comprises of one or more from the group: ROM (Read-Only Memory), PROM (Programmable ROM), EPROM (Erasable PROM), Flash memory, EEPROM (Electrically EPROM) and hard disk drive.

Further applications and advantages of the present invention will be apparent from the following detailed description.

Brief Description of the Drawings

The appended drawings are intended to clarify and explain different embodiments of the present invention, in which:

Fig. 1 shows an estimation device according to an embodiment of the present invention.

Fig. 2 shows a method according to an embodiment of the present invention.

Fig. 3 shows a user device according to an embodiment of the present invention.

Fig. 4 illustrates the transmissions from a serving cell and an interfering cell to a user device in a wireless communication system.

Fig. 5 illustrates the content of each RE of a serving cell and an interfering cell.

Fig. 6 shows a flow chart of an embodiment of the present invention.

Figs. 7 and 8 show performance results for embodiments of the present invention.

Detailed Description

In LTE systems, when the CRS of a serving cell is colliding with that of an interfering cell, the noise power estimation is easy to obtain using conventional solutions, such as iteratively estimating the channel response and the noise power. If the received signal is interfered by the interfering cell's control signal, the CRS of the serving cell may or may not collide with that of the interfering cell, which is dependent on the cell ID of the serving cell and the cell ID of the interfering cell. If both mentioned cells are assumed to have 2 transmit antennas, the CRS of the cells will collide if mod(N ^ll-^sever , 3) = mod(N%^ll-^intefer, 3), otherwise, the CRS will not collide. The control signal mentioned in this disclosure is in LTE systems the PDCCH control signal. However, it is not easy to obtain the noise power estimation when the CRS of the serving cell is not colliding with the CRS of the interfering cell. First of all, the aforementioned conventional solutions for channel estimation do not work in this non-colliding case. Secondly, even if the channel response of both cells are available, it's still not possible to reconstruct the PDCCH signal from the interfering cell and subtract it from the received signal. This is because the originally transmitted PDCCH signal of the interfering cell that interferes with that for the serving cell is unknown. On the other hand, the amplitude of the PDCCH signals of the serving cell and the interfering cell are unknown to the UE, and the position of both cells' PDCCH is also unknown. These facts make the noise estimation more difficult.

Therefore, an objective of embodiments of the invention is to provide an improved solution for noise power estimation. Especially, the present solution provides a solution for noise power estimations in the non-colliding case which is not possible with conventional solutions. The present solution is e.g. advantageous in LTE systems but is not limited thereof. Rather, applications of embodiments of the invention are much broader than to LTE systems only which is readily realized by the skilled person. Fig. 1 shows an estimation device 100 according to an embodiment of the invention. The estimation device 100 comprises a processor 102 which is configured to obtain a communication signal y comprising a plurality of Resource Elements (REs), e.g. time frequency slots. The communication signal y carries at least one first reference signal RS1 of a serving cell 502 and at least one second reference signal RS2 of at least one interfering cell 504 (see Fig. 4 illustrating the serving cell 502 and the interfering cell 504). The processor 102 is further configured to compute a first reconstructed reference signal for the serving cell 502. The processor 102 is further configured to compute a second reconstructed reference signal for the interfering cell 504. The processor 102 is further configured to provide a cancelled communication signal y^' based on the communication signal y, the first reconstructed reference signal and the second reconstructed reference signal. The processor 102 is further configured to compute a first noise power for a first resource element REO of the plurality of the resource elements REs based on the cancelled communication signal y^'. The processor 102 is further configured to compute a second noise power for a second resource element RE1 of the plurality of resource elements based on the cancelled communication signal y^'. The processor 102 is further configured to compute a noise power estimation Z based on the first noise power and the second noise power. The noise power estimation Z can be used to demodulate the PDCCH signal of both the serving cell and the interfering cell.

The communication signal y is in an example a superimposed signal which comprises at least one serving cell signal and at least one interfering cell signal. The reference signal may e.g. be a CRS in LTE and LTE-systems.

Fig. 2 shows a corresponding method 200 which may be executed in an estimation device 100, such as the one shown in Fig. 1. The method 200 comprises obtaining 202 a communication signal y comprising a plurality of REs. The communication signal y carries at least one first reference signal RS1 of a serving cell 502 and at least one second reference signal RS2 of at least one interfering cell 504. The method 200 further comprises computing 204 a first reconstructed reference signal for the serving cell 502. The method 200 further comprises computing 206 a second reconstructed reference signal for the interfering cell 504. The method 200 further comprises providing 208 a cancelled communication signal y^' based on the communication signal y, the first reconstructed reference signal and the second reconstructed reference signal. The method 200 further comprises computing 210 a first noise power for a first resource element E0 of the plurality of the REs based on the cancelled communication signal y^'. The method 200 further comprises computing 212 a second noise power for a second resource element RE1 of the plurality of REs based on the cancelled communication signal y^'. The method 200 further comprises computing 214 a noise power estimation Z based on the first noise power and the second noise power.

Fig. 3 shows a user device 300 comprising an estimation device 100, such as the one shown in Fig. 3. The user device 300 further comprises a receiver 104 communicably coupled with the processor 102 of the estimation device 100. The user device 300 may also comprise an antenna 106 coupled to the receiver 104 and being configured to receive wireless communication signals S in a cellular wireless communication system. The cellular system may in an embodiment be a OFDM system, such as LTE. Further, the mentioned reference signals may in this embodiment by CRSs, e.g. associated with physical control channels such as PDCCH.

The user device 300 or a User Equipment (UE), mobile station, wireless terminal and/or mobile terminal is enabled to communicate wirelessly in a wireless communication system, sometimes also referred to as a cellular radio system. The User Equipment (UE) may further be referred to as mobile telephones, cellular telephones, computer tablets or laptops with wireless capability. The UEs in the present context may be, for example, portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile devices, enabled to communicate voice and/or data, via the radio access network, with another entity, such as another receiver or a server. The UE can be a Station (STA), which is any device that contains an IEEE 802.1 1- conformant Media Access Control (MAC) and Physical Layer (PHY) interface to the Wireless Medium (WM)

Fig. 4 illustrates how the user device 300 receives a first signal S1 from a serving cell 502 represented by a first radio network node 502^' configured to serve the user device 300. It is also shown in Fig. 4 how an interfering cell 504 represented by a second radio network node 504^' transmits a second signal S2 which interferes with the first signal S1. The first signal S1 and the second signal S2 together form the superimposed signal S which is received by the user device 300 in Fig. 4. A radio network node, or base station, e.g. a Radio Base Station (RBS), which in some networks may be referred to as transmitter, "eNB", "eNodeB", "NodeB" or "B node", depending on the technology and terminology used. The radio network nodes may be of different classes such as e.g. macro eNodeB, home eNodeB or pico base station, based on transmission power and thereby also cell size. The radio network node can be a Station (STA), which is any device that contains an IEEE 802.1 1 -conformant Media Access Control (MAC) and Physical Layer (PHY) interface to the Wireless Medium (WM).

In the following disclosure some general scenarios, use cases and embodiments are described and explained for providing a deeper understanding of embodiments of the invention. These scenarios and use cases are set in LTE and/or LTE-A context with its relevant terminology and expressions. Hence, a user device 300 corresponds to a UE and a reference signal to a CRS in this context. However, embodiments of the invention are not limited to LTE systems.

Scenario 1 : in this scenario the serving cell(s) 502 and the interfering cell(s) 504 are transmitting references signals RS1 and RS2 corresponding to CRS, respectively. The communication signal y derived from the received signal S can be expressed as

where yp- is the received signal at j-th receiving antenna and i-th RE, h"_m is the channel response of j-th receiving antenna and m-th transmitting antenna on n-th cell, j}, is the transmitted signal from m-th transmitting antenna of n-th cell, which is unknown to the UE, a and β are the amplitude of the received signal, which is also unknown to the UE, and nj is the noise at j-th receiving antenna and i-th RE, which is considered to be Gaussian with zero mean and variance of σ². s„ is the CRS signal from m-th transmitting antenna of n-th cell, which is known to the UE. In this case the channel responses of 3 adjacent REs are considered to be identical.

At I in Fig. 5, it is shown how each block represents one RE from bottom to top of Fig. 5. The REs are indexed from 0 to 5 in the example in Fig. 5. The indices are repeated for the whole bandwidth but this is not shown in Fig. 5. In the example in Fig. 5 only 6 REs are considered but the present solution is not limited thereto. The severing cell's ID is in this particular example 1 , the REs for the serving cell 502 are indexed 1 , 4, 7, 10 and are reserved for the CRSs of the serving cell 502 which is shown at II. The interfering cell's ID is 0, and the REs for the interfering cell 504 are indexed 0, 3, 6, 9, and are reserved for the CRSs of the interfering cell 504 which is shown at III. At II and III in Fig. 5, transmitted signals from the serving cell 502 (II) and the interfering cell 504 (III), respectively are shown. The REs labeled CRS1 (1 ) and CRS1 (4) are reference signals of the serving cell 502, and the REs labeled Data1 (0), Data1 (2), Data1 (3), Data1 (5) are the control signal of the serving cell 502. Similarly, the REs labeled CRS2(0), CRS2(3) are the reference signal of the interfering cell 504 and the REs labeled Data2(1 ), Data2(2), Data2(4), Data2(5) are the control signal of the interfering cell 504. It is clear from Fig. 5 that the reference signals of the serving cell 502 and the interfering cell 504 are not mapped on the same REs. This case is denoted as the CRS non-colliding case. The received signal S is the sum of signal of at least one serving cell 502 and at least one interfering cell 504 that have propagated through a wireless channel, which is illustrated at IV of Fig. 5. In the received signal S, each RE comprises signals from the serving cell 502 and the interfering cell 504. The received signal S could comprise CRSs and control signals, like RE0, RE1 , RE3, RE4, or a combination of control signals only as for RE2 and RE5.

The received CRS signals of the serving cell 502 and the interfering cell 504 can be reconstructed by multiplying the channel estimation h"_m with the transmitted CRS signal s™ , which is known to the UE if the UE knows the cell ID of each cell. The reconstructed signal can be cancelled from the communication signal y, and the communication signal y after CRS cancellation y' can be expressed as

which is shown in V of Fig. 5. In V of Fig. 5, the CRS signal of both the serving cell 502 and the interfering cell 504 are removed from the communication signal y. The power of the communication signal after CRS cancellation y' is the product of communication signal after CRS cancellation and its conjugation, i.e.:

Ilyill² = yi * (yi)^* where (yj)^* is the conjugation of

All the power of the communication signal after CRS cancellation y' on each receiver antenna and RE is calculated as:

where

In this case the PDCCH signals and noise are considered independent.

In an embodiment, the noise power estimation Z is the sum of noise power of REs' on the CRS positions of the serving cell 502 and the interfering cell 504 subtracted by the noise power of REs not on CRS positions of either the serving cell 502 or the interfering cell 504.

In the example illustrated in Fig. 5, the noise power of the REs on the CRS position are the noise power of the first two REs (i.e. RE0 and RE1 ), and the noise power of the RE not on the CRS position is the noise power of the third RE (i.e. RE2). Therefore, in this example the noise power estimation Z can be expressed as

If we take the expectation of noise power estimation Z over the whole bandwidth of the first PDCCH symbol, and assume that the signals are independent, then we will get the noise power estimation Z as

E{Z) = 2σ² Scenario 2: in this scenario the serving cell 502 is not transmitting any control signals (such as PDCCH), but the interfering cell 504 is transmitting control signals. The communication signal after C S cancellation y^' can be expressed as:

The power of the communication signal after CRS cancellation y^' is

where

Here, the noise power estimation Z is the sum of first two REs' power subtracted by the sum of third RE's noise power,

z = WvlW² + WvlW ² + Wvl W ² + Wvl W ² - Uvi W² - Wvi W²

If we take the expectation of noise power estimation Z over the whole bandwidth of the first PDCCH symbol, and assume that the signal is independent, then we will get the noise power estimation by

E{Z) = 2σ²

Scenario 3: in this scenario the serving cell 502 is transmitting control signals, such as PDCCH, whilst the interfering cell 504 is not transmitting any control signals at all. The result for scenario 3 is the same as for scenario 2. In scenario 2, the serving cell 502 is not transmitting control signals at all whilst the interfering cell 504 is transmitting control signals. If we change the point of view and swap the serving cell 502 with the interfering cell 504, we will get scenario 3 and therefore the same result as in scenario 3.

Scenario 4: in this scenario no one of the serving cell 502 or the interfering cell 504 are transmitting control signals, such as PDCCH. The communication signal after CRS cancellation y^' can be expressed as:

and the power of the communication signal after CRS cancellation y^' is

Here the nose power estimation Z is the sum of first two REs' noise power subtracted by the third RE's noise power,

z = l lyil l² + Nyll I² + l lyf l I² + l |y₂ ²| l² - l lyf l I² - l ly₂ ³| l²

= 2σ²

If we take the expectation of the nose power estimation Z over the whole bandwidth of first PDCCH symbol, and assume that the control signals are independent, then we will get the noise power estimation by

E{Z) = 2σ² Sometimes, the noise power estimation Z for one symbol is not stable. However, it has been realized that the noise power estimation Z for one symbol can be filtered with a noise power estimation from at least another subframe to obtain improved estimation performance. In an embodiment the subframes are continuous in time. The filter can e.g. be a Finite Impulse Response (FIR) filter, an Infinite Impulse Response (MR) filter or another type of suitable filter know in the art. In an embodiment, the MR filter can be expressed as

FZ(i) = aFZ i - 1) + (1 - a)E(Z{i)) where a is the filter coefficient, £(Z(i)) is the noise estimation of the i-th subframe, and FZ{i - 1) is the filtered noise estimation of the (i-1 )-th subframe.

The above results show that the present solution can estimate the noise power correctly no matter if the serving cell 502 or the interfering cell 504 is transmitting a control signal or not. Furthermore, the present solution is not sensitive to the amplitude of the PDCCH signal of the serving cell 502 or the interfering cell 504, since this information is not needed in the present solution. Fig. 6 shows a flow chart of an embodiment of the invention which illustrates and covers some of the aspects describe above:

At I in Fig. 6, a user device 300 receives a wireless communication signal S corresponding to the communication signal y.

At II in Fig. 6, the estimation device 100 of the user device 300 estimates the channel and outputs the channel response h.

At III in Fig. 6, the estimation device 100 reconstructs the reference signals by multiplying the channel response h with the corresponding known reference signals s.

At IV in Fig. 6, the estimation device 100 computes a cancelled communication signal y^' based on the communication signal y and the reconstructed reference signal from III. The "+" sign at IV illustrates adding the communication y whilst the "-" sign at IV illustrates subtracting the reconstructed reference signal from III.

At V in Fig. 6, the estimation device 100 computes the noise power for each RE of the communication signal y based on the cancelled communication signal y^'. In this example there are three REs, namely RE0, RE1 , RE2, and hence corresponding first, second and third noise powers are computed at V.

At VI in Fig. 6, the estimation device 100 computes the noise power estimation Z by subtracting the third noise power from the sum of the first noise power and the second noise power.

At VII in Fig. 6, the estimation device 100 computes the averaged noise power estimation E(Z) by averaging the noise power estimation Z from VI over the whole system bandwidth to obtain an improved noise power estimation.

At VIII in Fig. 6, the estimation device 100 computes and provide the final noise power estimation FZ by filtering the averaged noise power estimation E{Z) over at least two continuous subframes so as to provide an even more improved noise power estimation.

The MMSE detection performance of a PDCCH control signal using noise power estimations Z provided by embodiments of the invention is shown in Fig. 7. The simulation parameters are stated herein. The serving cell 502 and the interfering cell 504 both have two transmit antennas each; the DCI length of both cells are 59; the aggregation level is 2; the channel of the serving cell is EVA 37.8 km/h with low correlation; and the channel of the interfering cell is EVA 2.7 km/h with medium correlation; the cell ID of the serving cell is 1 , and the cell ID of the interfering cell is 0; and the UE has two receiver antennas.

In Fig. 7 the x-axis represents Signal-to-Noise Ratio (SNR) in dB and the y-axis represents the Block Error Rate (BLER). The UE uses eSLIC detection method in this case. The UE using the present solution can achieve almost the same performance as for the ideal noise power estimation as shown in Fig. 7. On the other hand, if the UE uses a conventional solution, such as the DFT based noise power estimation, the performance degrades substantially because the noise power estimation of the conventional DFT based solution is not accurate enough.

Fig. 8 shows a comparison of an ideal SNR, a SNR estimation based on the DFT based solution and a SNR estimation based on the proposed solution with the same parameters setting as in Fig. 7. The x-axis shows the real SNR in dB and the y-axis shows the estimated SNR in dB. Fig. 8 shows that the proposed solution is closer in SNR estimation to the ideal SNR than that for the DFT based method according to the conventional solution. Furthermore, any method according to the present invention may be implemented in a computer program, having code means, which when run by processing means causes the processing means to execute the steps of the method. The computer program is included in a computer readable medium of a computer program product. The computer readable medium may comprises of essentially any memory, such as a ROM (Read-Only Memory), a PROM (Programmable Read-Only Memory), an EPROM (Erasable PROM), a Flash memory, an EEPROM (Electrically Erasable PROM), or a hard disk drive.

Moreover, it is realized by the skilled person that the present user device 300 comprises the necessary communication capabilities in the form of e.g., functions, means, units, elements, etc., for performing the present solution. Examples of other such means, units, elements and functions are: processors, memory, buffers, control logic, encoders, decoders, rate matchers, de-rate matchers, mapping units, multipliers, decision units, selecting units, switches, interleavers, de-interleavers, modulators, demodulators, inputs, outputs, antennas, amplifiers, receiver units, transmitter units, DSPs, MSDs, TCM encoder, TCM decoder, power supply units, power feeders, communication interfaces, communication protocols, etc. which are suitably arranged together for performing the present solution. Especially, the processor of the present user device 300 may comprise, e.g., one or more instances of a Central Processing Unit (CPU), a processing unit, a processing circuit, a processor, an Application Specific Integrated Circuit (ASIC), a microprocessor, or other processing logic that may interpret and execute instructions. The expression "processor" may thus represent a processing circuitry comprising a plurality of processing circuits, such as, e.g., any, some or all of the ones mentioned above. The processing circuitry may further perform data processing functions for inputting, outputting, and processing of data comprising data buffering and device control functions, such as call processing control, user interface control, or the like.

Finally, it should be understood that embodiments of the present invention are not limited to the embodiments described above, but also relate to and incorporate all embodiments within the scope of the appended independent claims.

Claims

1. Estimation device (100) comprising a processor (102) configured to

obtain a communication signal (y) comprising a plurality of resource elements ( Es), the communication signal (y) carrying at least one first reference signal (RS1 ) of a serving cell (502) and at least one second reference signal (RS2) of at least one interfering cell (504), compute a first reconstructed reference signal for the serving cell (502),

compute a second reconstructed reference signal for the interfering cell (504), provide a cancelled communication signal (y^') based on the communication signal (y), the first reconstructed reference signal and the second reconstructed reference signal,

compute a first noise power for a first resource element (RE0) of the plurality of the resource elements (REs) based on the cancelled communication signal (y^'),

compute a second noise power for a second resource element (RE1 ) of the plurality of resource elements (REs) based on the cancelled communication signal (y^'),

compute a noise power estimation (Z) based on the first noise power and the second noise power.

2. Estimation device (100) according to claim 1 , wherein the processor (102) is configured to compute the noise power estimation (Z) based on a sum the first noise power and the second noise power.

3. Estimation device (100) according to claim 2, wherein the processor (102) is configured to compute at least one third noise power for a third resource element (RE2) among the plurality of resource elements (REs), the third resource element (RE2) being different from the first resource element (RE0) and the second resource element (RE1 ),

compute the noise power estimation (Z) based on subtracting the third noise power from the sum of the first noise power and the second noise power.

4. Estimation device (100) according to claim 3, wherein no reference signal is mapped on the third resource element (RE2).

5. Estimation device (100) according to claim 3 or 4, wherein the processor (102) is configured to compute the noise power estimation (Z) based on averaging the noise power estimation (Z) over the whole system bandwidth.

6. Estimation device (100) according to claim 5, wherein the processor (102) is configured to compute the noise power estimation (Z) based on filtering the averaged noise power estimation (Z) over at least two subframes.

7. Estimation device (100) according to any of the preceding claims, wherein the processor (102) is configured to compute the first reconstructed reference signal and the second reconstructed reference signal based on

estimating a first channel response for the serving cell (502) and a second channel response for the interfering cell (504),

multiplying the first channel response with the first reference signal ( S1 ) so as to provide the first reconstructed reference signal,

multiplying the second channel response with the second reference signal (RS2) so as to provide the second reconstructed reference signal.

8. Estimation device (100) according to claim 7, wherein the processor (102) is configured to provide the cancelled communication signal (y^') based on subtracting the first reconstructed reference signal and the second reconstructed reference signal from the communication signal (y).

9. Estimation device (100) according to claim 8, wherein the power of the cancelled communication signal (y^') is a product of the cancelled communication signal (y^') with its conjugate.

10. Estimation device (100) according to any of the preceding claims, wherein the first reference signal (RS1 ) is mapped on at least one first resource element (RE0) and the second reference signal (RS2) is mapped on at least one second resource element (RE1 ) different from the first resource element (RE0).

1 1. User device for a cellular communication system (500), the user device (300) comprising an estimation device (100) according to any of the preceding claims,

a receiver (104) configured to

receive a wireless communication signal (S) corresponding to the communication signal

(y).

12. User device (300) according to 1 1 , wherein the cellular communication system (500) is an OFDM system.

13. User device (300) according to 12, wherein the first reference signal (RS1 ) and the second reference signal (RS2) are Common Reference Signals, CRSs.

14. Method (200) comprising:

obtaining (202) a communication signal (y) comprising a plurality of resource elements

(REs), the communication signal (y) carrying at least one first reference signal (RS1 ) of a serving cell (502) and at least one second reference signal (RS2) of at least one interfering cell (504),

computing (204) a first reconstructed reference signal for the serving cell (502), computing (206) a second reconstructed reference signal for the interfering cell (504), providing (208) a cancelled communication signal (y') based on the communication signal (y), the first reconstructed reference signal and the second reconstructed reference signal,

computing (210) a first noise power for a first resource element (RE0) of the plurality of the resource elements (REs) based on the cancelled communication signal (y^'),

computing (212) a second noise power for a second resource element (RE1 ) of the plurality of the resource elements (REs) based on the cancelled communication signal (y^'), computing (214) a noise power estimation (Z) based on the first noise power and the second noise power.

15. Computer program with a program code for performing a method according to claim 14 when the computer program runs on a computer.