WO2018014963A1

WO2018014963A1 - Estimator and method for computing a joint power boosting probability for control channels symbols

Info

Publication number: WO2018014963A1
Application number: PCT/EP2016/067434
Authority: WO
Inventors: Junshi Chen; Peter Almers; Jianjun Chen
Original assignee: Huawei Technologies Co., Ltd.
Priority date: 2016-07-21
Filing date: 2016-07-21
Publication date: 2018-01-25

Abstract

The present invention relates to an estimator (100) comprising a processor (102) configured to obtain a received communication signal (y) comprising a control channel symbol (s) transmitted on a plurality of resource elements (RE1, RE2,..., RE_K), a) compute a power boosting probability (p _k) for each resource element (REk) of the plurality of resource elements (RE1, RE2,..., RE_K) based on an estimate (q _k) of the control channel symbol (s) transmitted on the resource element (REk) and an associated variance (δ² _k), b) compute a combined power boosting probability for the plurality of resource elements (RE1, RE2,..., RE_K) based on computed power boosting probabilities for each resource element (REk) of the plurality of resource elements (RE1, RE2,..., RE_K), c) compute a joint probability for the control channel symbol (s) based on the combined power boosting probability. Furthermore, the present invention also relates to a receiving device, a corresponding method, a computer program, and a computer program product.

Description

ESTIMATOR AND METHOD FOR COMPUTING A JOINT POWER BOOSTING

PROBABILITY FOR CONTROL CHANNELS SYMBOLS

Technical Field

The invention relates to an estimator and a receiving device comprising such an estimator. Furthermore, the invention also relates to corresponding methods, a computer program, and a computer program product.

Background

In 3GPP Long Term Evolution (LTE) and LTE-Advanced (LTE-A), 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, the UE cannot get any Physical Downlink Shared Channel (PDSCH) information which is critical for, e.g., data services and user experience. At the cell edge, the PDCCH of the serving cell is often impaired by interference with the PDCCH of neighbouring cells. The information about the distribution of neighbouring cells' PDCCH is not known to the UE. Furthermore, the power of the PDCCH of the serving cell and the power of the PDCCH of the neighbouring cells are not known to the UE either. This makes demodulating the PDCCH of the serving cell more difficult for the UE since traditional algorithms, such as minimum mean square error (MMSE) or symbol level interference cancellation (SLIC), are based on the assumption that the power of the PDCCH of the serving cell and the power of the PDCCH of the neighbouring cells are known. From here on a neighbouring cell is also denoted as an interfering cell in the present disclosure. In enhanced SLIC (eSLIC) an algorithm is proposed which provides more robust PDCCH link level performance in scenarios with power ambiguity of the serving cell and the interfering cell. The eSLIC algorithm takes explicit consideration of the unknown PDCCH power control parameters at both the serving and the interfering cell(s). Summary

An objective of embodiments of the invention is to provide a solution which mitigates or solves the drawbacks and problems of prior solutions.

Another objective of embodiments of the invention is to further improve the performance of interference cancellation algorithms known in the art, such as eSLIC. 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 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 estimator comprising a processor configured to

obtain a received communication signal comprising a control channel symbol transmitted on a plurality of resource elements,

a) compute a power boosting probability for each resource element of the plurality of resource elements based on an estimate of the control channel symbol transmitted on the resource element and an associated variance,

b) compute a combined power boosting probability for the plurality of resource elements based on computed power boosting probabilities for each resource element of the plurality of resource elements, and

c) compute a joint probability for the control channel symbol based on the combined power boosting probability.

A number of advantages are provided by an estimator according to the first aspect. The combined power boosting probability is not used in prior solutions. Consequently, the joint probability which is computed based on the combined power boosting probability will be more accurate than prior solutions. Thereby, an improved probability for the control channel symbol is provided. Further, the joint probability for the control channel symbol may be advantageously used in prior algorithms known in the art for interference cancellation, such as SLIC and eSLIC. In a first possible implementation form of an estimator according to the first aspect, the processor is configured to

d) compute a respective mean for each resource element of the plurality of resource elements based on the joint probability,

e) subtract from the received communication signal the computed mean for each resource element so as to obtain a subtracted received communication signal,

f) compute a respective variance for each resource element of the plurality of resource elements based on the joint probability, g) filter the subtracted received communication signal with the computed variance for each resource element so as to obtain the estimate of the control channel symbol at a) for each resource element. The first implementation form provides more accurate mean and variance since the mean and variance are based on the joint probability. Therefore, the filtered subtracted received communication signal contains less interference. This will make the estimate of the control channel symbol more reliable. In a second possible implementation form of an estimator according to the first implementation form of the first aspect, the processor is configured to

repeat a) to g) iteratively.

The second implementation form provides an iterative approach which will improve the estimate of the control channel symbol probability.

In a third possible implementation form of an estimator according to the second implementation form of the first aspect, the estimate of the control channel symbol and the associated variance for each resource element at a) in a first iteration is obtained from MMSE estimation.

By using the MMSE estimate in the first iteration easy implementation with good performance is provided with the third implementation form.

In a fourth possible implementation form of an estimator according to the second or third implementation form of the first aspect, the processor is configured to

stop the iterations when the combined power boosting probability in two consecutive iterations changes less than a threshold value.

The fourth implementation form will provide a stop criterion when the combined power boosting probability converges to a stable value, and thereby further computations related to iterations are not needed.

In a fifth possible implementation form of an estimator according to the fourth implementation form of the first aspect, the processor is configured to

provide the estimate of the control channel symbol at g) as the final estimate for each resource element. The fifth implementation form provides an estimate of the control channel symbols that is much more accurate than the estimate according to prior solutions.

In a sixth possible implementation form of an estimator 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 combined power boosting probability based on the product of the power boosting probability for each resource element of the plurality of resource elements. The sixth implementation form takes advantage of the fact that in some cases the plurality of resource elements have the same power boosting value. By multiplying the power boosting probabilities of the plurality of resource elements together a combined power boosting probability is obtained which is more accurate than the power boosting probability for a single resource element.

In a seventh possible implementation form of an estimator according to the sixth implementation form of the first aspect, the received communication signal comprises a plurality of control channel symbols of at least one serving cell,

and the processor is configured to

compute the combined power boosting probability based on

where is tne product of the power boosting probabilities for all resource

elements of the plurality of resource elements given the estimated signal q_iik, where i is the cell index and k is the resource element index.

The seventh implementation form provides a closed form expression for computing the combined power boosting probability.

In an eight possible implementation form of an estimator 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 joint probability based on the product of the combined power boosting probability and a probability for the control channel symbol

The eighth implementation form provides a more accurate joint probability since the joint probability in this implementation form is based on the combined power boosting probability, which is more accurate than the power boosting probability for a single resource element. In a ninth possible implementation form of an estimator according to the eight implementation form of the first aspect, the received communication signal comprises a plurality of control channel symbols of at least one serving cell, wherein the processor is configured to compute the joint probability

based on

where is the

probability for the control channel symbol given the estimated signal for cell i at

resource element

The ninth implementation form provides a closed form expression for the joint probability.

In a tenth possible implementation form of an estimator according to any of the preceding implementation forms of the first aspect or to the first aspect as such, the control channel symbol is transmitted with the same power boosting value in the plurality of resource elements. According to a second aspect of the invention, the above mentioned and other objectives are achieved with a receiving device for a wireless communication system, the receiving device comprising

an estimator according to any of the preceding implementation forms of the first aspect or to the first aspect as such, and

a receiver configured to

receive the communication signal in the wireless communication system, and provide the received communication signal to the estimator.

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

obtaining a received communication signal comprising a control channel symbol transmitted on a plurality of resource elements,

a) computing a power boosting probability for each resource element of the plurality of resource elements based on an estimate of the control channel symbol transmitted on the resource element and an associated variance, b) computing a combined power boosting probability for the plurality of resource elements based on computed power boosting probabilities for each resource element of the plurality of resource elements,

c) computing a joint probability for the control channel symbol based on the combined power boosting probability.

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

d) computing a respective mean of the estimate for each resource element of the plurality of resource elements based on the joint probability,

e) subtracting from the received communication signal the computed mean for each resource element so as to obtain a subtracted received communication signal,

f) computing a respective variance for each resource element of the plurality of resource elements based on the joint probability, and

g) filtering the subtracted received communication signal with the computed variance for each resource element so as to obtain the estimate of the control channel symbol at a) for each resource element.

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

repeating a) to g) iteratively.

In a third possible implementation form of a method according to the second implementation form of the third aspect, the estimate of the control channel symbols and the associated variance for each resource element at a) in a first iteration is obtained from MMSE estimation.

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

stopping the iterations when the combined power boosting probability in two consecutive iterations changes less than a threshold value.

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

providing the estimate of the control channel symbol at g) as the final estimate for each resource element. In a sixth possible implementation form of a 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 combined power boosting probability based on the product of the power boosting probability for each resource element of the plurality of resource elements.

In a seventh possible implementation form of a method according to the sixth implementation form of the third aspect, the received communication signal comprises a plurality of control channel symbols of at least one serving cell, the method comprises

computing the combined power boosting probability ν based on

where '^{s tne} product of the power boosting probabilities for all resource

elements of the plurality of resource elements given the estimated signal q_iik, where i is the cell index and k is the resource element index. In an eighth possible implementation form of a 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 joint probability based on the product of the combined power boosting probability and a probability for the control channel symbol

In a ninth possible implementation form of a method according to the eight implementation form of the third aspect, the received communication signal comprises a plurality of control channel symbols of at least one serving cell, the method comprises

computing the joint probability

based on

where is the

resource element k.

In a tenth possible implementation form of a method according to any of the preceding implementation forms of the third aspect or to the third aspect as such, the control channel symbol is transmitted with the same power boosting value in the plurality of resource elements.

The advantages of any method according to the third aspect of the invention are the same as those for the corresponding estimator according to the first aspect. Embodiments of the invention also relate 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 invention. Further, the invention also relates to a computer program product comprising a computer readable medium and said 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 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 invention, in which:

Fig. 1 shows an estimator according to an embodiment of the invention.

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

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

Fig. 4 shows a communication system in which a receiving device according to an embodiment of the invention receives a communication signal from a network node.

Fig. 5 shows a flow chart of a method according to a further embodiment of the invention.

Fig. 6 shows performance results of embodiments of the invention.

Detailed Description

Fig. 1 shows an estimator 100 according to an embodiment of the invention. The estimator 100 comprises a processor 102 configured to obtain a received communication signal y comprising at least one control channel symbol s transmitted on a plurality of resource elements RE1 , RE2,..., RE_K (see Fig. 3), wherein K denotes the total number of REs. The processor 102 is further configured to a) compute a power boosting probability p_k for each resource element REk of the plurality of resource elements RE1 , RE2,..., RE_K based on an estimate q_k of the control channel symbol s transmitted on the resource element REk and an associated variance 5 , wherein k is the RE index. The processor 102 is further configured to b) compute a combined power boosting probability for the plurality of resource elements RE1 , RE2,..., RE_K based on computed power boosting probabilities for each resource element REk of the plurality of resource elements RE1 , RE2,..., RE_K. The processor 102 is further configured to c) compute a joint probability for the control channel symbol s based on the combined power boosting probability. The estimator 100 may be provided as a standalone device in an embodiment. However, in another embodiment the estimator 100 is fully or semi-integrated in another device, such as a receiving device configured for wireless communications. Fig. 2 shows a corresponding method 200 according to an embodiment of the invention which, e.g., may be executed in an estimator 100, such as the one shown in Fig. 1. The method 200 comprises obtaining 202 a received communication signal y comprising a control channel symbol s transmitted on a plurality of resource elements RE1 , RE2,..., RE_K. The method 200 further comprises computing 204 a power boosting probability p_k for each resource element REk of the plurality of resource elements RE1 , RE2,..., RE_K based on an estimate q_k of the control channel symbol s transmitted on the resource element REk and an associated variance 5 . The method 200 further comprises computing 206 a combined power boosting probability for the plurality of resource elements RE1 , RE2,..., RE_K based on computed power boosting probabilities for each resource element REk of the plurality of resource elements RE1 , RE2,..., RE_K. The method 200 further comprises computing 208 a joint probability for the control channel symbol s based on the combined power boosting probability.

Fig. 3 shows a receiving device 300 according to an embodiment of the invention. The receiving device 300 comprises an estimator 100 according to an embodiment of the invention. The estimator 100 is in this embodiment integrated in the receiving device 300. Further, the receiving device 300 further comprises a transceiver 302 communicatively coupled to the estimator 100 with communication means 308 known in the art and shown as an arrow. The transceiver 302 may further be coupled to an antenna 306 configured for wireless communications in a wireless communication system, such as LTE.

Fig. 4 illustrates a wireless communication system 500, such as LTE. The wireless communication system 500 comprises a receiving device 300 which includes an estimator 100 according to embodiments of the invention. The receiving device 300 may, e.g., be a UE in a LTE system. The receiving device 300 receives downlink (DL) transmissions from an access network node 400, such as a base station. The downlink transmissions comprise at least one communication signal y in which at least one control channel symbol s is transmitted on a plurality of resource elements RE1 , RE2, RE_K. The receiving device 300 may forward the communication signal y to the estimator 100 directly or after suitable processing, such as down-converting of the radio signal into a corresponding baseband signal.

The invention is based on the insight that in a physical control channel (such as PDCCH), the Resource Elements (REs) within one CCE (Control Channel Element) have in some cases the same power. This applies to both the physical control channel of the serving cell and to the physical control channel(s) of the interfering cell(s). This fact can be used to refine the power boosting value estimate according to embodiments of the invention. Though the interference experienced in one CCE of the serving cell may come from CCEs of different interfering cells, the interference in one or more Resource Element Groups (REGs) of the serving cell comes from the same interfering cells. Accordingly, more than one RE is used for estimating the power boosting value(s).

In an embodiment based on 3GPP LTE, the PDCCH is transmitted on an aggregation of one or more consecutive CCEs, wherein a CCE corresponds to 9 REGs. The number of REGs not assigned to Physical Control Format Indicator Channel (PCFICH) or Physical Hybrid-ARQ Indicator Channel (PHICH) is N_REG. The CCEs available in LTE are numbered from 0 to N_CCE— 1, where The REGs are used for defining the mapping of control channels to

REs. A REG is represented by the index pair (k , I ) of the RE with the lowest RE index k in the group I with all REs in the group having the same value of I. The set of REs k, I) in a REG may depend on the number of cell-specific reference signals (which may be configured according to standards).

Mapping of a symbol-quadruplet onto a REG represented

by a RE index pair k , I ) is defined such that elements z(n) are mapped to REs k, Ϊ) of the REG not used for cell-specific reference signals in increasing order of n and k. In one example, a single cell-specific reference signal is configured, and cell-specific reference signals are present on antenna ports 0 and 1 for the purpose of mapping a symbol-quadruplet to a REG. In another example, the number of cell-specific reference signals is equal to the number of antenna ports used for cell-specific reference signals. The UE does not make any assumptions about REs reserved for reference signals but not used for transmission of a reference signal.

In the present disclosure a system model is introduced for providing a deeper understanding of embodiments of the invention. In this respect LTE and LTE-A terminology, system concepts and assumptions are sometimes used. The skilled person realises that embodiments of the invention are not limited to such systems.

The received signal y at the /c-th RE can be written as

where index 1 in this particular example corresponds to the index of a serving cell, and index

corresponds to the index of one or more interfering cells; y k) is the N received signal, where

is the number of UE receiver antennas is the

channel vector; are the unknown PDCCH power boosting values of

cell are the unknown (e.g., QPSK) symbols transmitted on one or more REs

on which the PDCCH signal is mapped; and n is the N

with noise power

. We want to estimate the unknown PDCCH power boosting values

Using MMSE detection with the assumption that the power boosting value of the serving cell and the power boosting value of the interfering cell are 1 , the estimate of transmitted symbol is obtained as where q_iik is the estimate of the transmitted symbol and is the channel matrix with

channel vectors The estimate of the transmitted symbol is

also referred to herein as the soft symbol estimate. The likelihood of the estimate is given by

^

where is the variance of interference plus noise after MMSE filtering, e.g.,

where I is an identity matrix.

The posterior probability P is obtained using Bayesian theory as

where Ω is the set of the QPSK constellation points, and γ is the set of power boosting values. A mean of the soft symbol estimate q and the variance of the soft symbol estimate

can be calculated as

The mean of the soft symbol estimate also takes the power boosting value into

account, i.e.

The variance of the soft symbol estimate _k also includes averaging across possible power boosting value as

The received signal after Interference Cancellation (IC) can be obtained as

The after IC can be equalized with, e.g., a MMSE filter as

where is the residual interference covariance matrix after IC given by

where

The probability for a power boosting value

may be a slowly varying function of the power boosting value compared to the exponent function in equation [3]. Closed form expressions for are then given by

where ) in equation [14], and l in equation [15].

According to equation [4] above, the posterior probability of βι and s_iik can be expressed as

Based on the observation that the REs of the PDCCH of the serving cell inside the same REG have the same power boosting value and experience the same level of interference, the estimate of the probability of can be refined by combining the probability of all the REs inside

the same REG as

where K is the number of REs that have the same power boosting value, q_{i k} is the MMSE estimate of is the transmitted symbol of the RE.

Normally, the power boosting value and the transmitted symbol

are assumed to be independent, which means that the joint probability of given soft symbol estimate , i.e.

is the product of is the posterior

probability of the power boosting value given the soft symbol estimate and

is the posterior probability of transmitted signal given the soft symbol estimate

Therefore, the joint probability

can be expressed as

Based on the present refined estimate of the power boosting value /?; in equation [18], an improved posterior probability estimate of the transmitted signal with power boosting

given the soft symbol estimates is provided by the present

solution as

Based on the assumption that the power boosting value and s are independent, the

posterior probability estimate of the transmitted signal with power boosting value given

the soft symbol estimates is equal to the product of the

posterior probability of the power boosting value given the soft symbol estimates

anc' tne posterior probability of the transmitted signal given the soft

symbol estimates

Furthermore, since the soft symbol estimates from symbol

are independent to the transmitted symbol, the equation

witn

This improved estimate of the power boosting values can be used to update the SLIC algorithm, or the eSLIC algorithm, and thereby provide improved interference cancellation compared to prior solutions. It should, however, be noted that the power boosting estimates provided by the present estimator 100 are not limited thereto. Fig. 5 shows a block diagram comprising processing blocks I) to VI I) according to a further embodiment of the invention in which the present solution is combined with the SLIC algorithm in an iterative manner. The flow chart of Fig. 5 illustrates some important aspects and embodiments of the invention which will be explained more in detail in the following disclosure. Block I): The received communication signal y is provided to block I). The power boosting values for the interfering cell and the serving cell are set to 1 or are normalized. The soft symbol estimate q_iik is estimated based on per RE MMSE detection.

The variance of the soft symbol estimate, i.e.

is initialized by the identity matrix in block I) as

where is the MMSE filter.

The soft symbol estimate of the i-th cell is

and is initially set to 0 in this particular example.

Block II): From the soft symbol estimates q_iik in block I), the posterior probabilities

and are computed in block II) using expressions

Block III): The combined probability estimate of from multiple REs with the same βι is

computed in block III) using expression

Block IV): The posterior probability of is updated in block IV) using

expression

Block V): The posterior probability from block is used to refine the

soft symbol estimate q_iik in block V) by the updated mean, , and variance, _k according

to expressions

Block VI): Based on the updated mean and variance from block V) an improved soft

symbol estimate

is obtained from soft symbol cancellation by using the MMSE SLIC in block V). The received signal y after interference cancellation in block V) can be computed using the expression

Thereafter is equalized with a MMSE filter as

where R_iik is the residual interference covariance matrix after IC is

and where

The updated variance of interference plus noise after MMSE filter, i.e.

is given as

Block VII): The updated variance of the interference plus noise after MMSE filtering

is fed as input to block II). Further, the soft symbol estimate q_iik in block II) is replaced with the improved soft symbol estimate

computed in block VI), and the variance <¾, is replaced with the updated variance computed in block VI).

Blocks II) to VII) are executed iteratively for a number of iterations according to an embodiment.

The procedure can be repeated a predetermined number of times in an embodiment. In another embodiment a stop criterion for the iterations is applied. According to this latter embodiment the processor 102 is configured to stop the iterations when the combined power boosting probability in two consecutive iterations changes less than a threshold value, e.g., 0.05 or any other suitable value. If the difference between two consecutive iterations is less than the threshold value, it means that the combined power boosting probability is converging to a stable value, and therefore no further iterations are needed implying reduced computations and hence reduced power consumption.

Finally, in the last iteration the processor 102 is configured to provide the estimate q_k of the control channel symbols s at processing step g) as the final estimate for each resource element REk.

The performance of embodiments of the invention is shown in Fig. 6. The X-axis in Fig. 6 shows the Signal to Noise Ratio (SNR) in dB and the Y-axis in Fig. 6 shows the block error rate (BLER). The simulation parameters are: 1 serving cell and 2 interfering cells, cell id are 0,3,6, all the cells have 2 transmit antennas, the interfering cells power are both 3dB higher than that for the serving cell, the serving cell's REs are all interfered by the interfering cells, and the CCE number is 2. The PDCCH detection performance for the serving cell is compared between a prior solution and the proposed solution as shown in Fig. 6. The prior solution uses only one RE to estimate the power boosting probability βι , on the other hand the proposed solution uses 4 REs inside the same REG to refine the estimate of the power boosting probability We can see from Fig. 6 that the proposed solution has much better performance than the prior solution.

A receiving device 300 described herein may be any of a User Equipment (UE), mobile station (MS), wireless terminal or mobile terminal which is enabled to communicate wirelessly in a wireless communication system, sometimes also referred to as a cellular radio system. The UE may further be referred to as a mobile telephone, cellular telephone, computer tablet or laptop 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 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). Further, standards promulgated by the IEEE, the Internet Engineering Task Force (IETF), the International Telecommunications Union (ITU), the 3GPP standards, fifth-generation (5G) standards and so forth, are supported. In various embodiments, the receiving device 100 may communicate information according to one or more IEEE 802 standards including IEEE 802.1 1 standards (e.g., 802.1 1 a, b, g/h, j, n, and variants) for WLANs and/or 802.16 standards (e.g., 802.16-2004, 802.16.2-2004, 802.16e, 802.16f, and variants) for WMANs, and/or 3GPP LTE standards. The receiving device 100 may communicate information according to one or more of the Digital Video Broadcasting Terrestrial (DVB-T) broadcasting standard and the High performance radio Local Area Network (HiperLAN) standard.

An access network node 400 described herein may also be denoted as an access node or an access point or a base station, e.g., a Radio Base Station (RBS), which in some networks may be referred to as transmitter, "eNB", "eNodeB", "NodeB", "gNB" or "B node", depending on the technology and terminology used. The access network nodes may be of different classes, such as macro eNodeB, home eNodeB or pico base station, based on transmission power and thereby also cell size. The access 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). The access network node 300a, 300b may also be a network node in a wired communication system. Further, standards promulgated by the IEEE, the Internet Engineering Task Force (IETF), the International Telecommunications Union (ITU), the 3GPP standards, fifth-generation (5G) standards and so forth are supported. In various embodiments, the network node 400 may communicate information according to one or more IEEE 802 standards including IEEE 802.1 1 standards (e.g., 802.1 1 a, b, g/h, j, n, and variants) for WLANs and/or 802.16 standards (e.g., 802.16-2004, 802.16.2-2004, 802.16e, 802.16f, and variants) for WMANs, and/or 3GPP LTE standards. The access network node 300a, 300b may communicate information according to one or more of the Digital Video Broadcasting Terrestrial (DVB-T) broadcasting standard and the High performance radio Local Area Network (HiperLAN) standard.

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 comprise 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 receiving device 100 or user device 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 102 of the present estimator 100 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 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 the present invention is not limited to the embodiments described above, but also relates to and incorporates all embodiments within the scope of the appended independent claims.

Claims

1 . Estimator (100) comprising a processor (102) configured to

obtain a received communication signal (y) comprising a control channel symbol (s) transmitted on a plurality of resource elements (RE1 , RE2,..., RE_K),

a) compute a power boosting probability (p_fc) for each resource element (REk) of the plurality of resource elements (RE1 , RE2,..., RE_K) based on an estimate (q_k) of the control channel symbol (s) transmitted on the resource element (REk) and an associated variance

{sl),

b) compute a combined power boosting probability for the plurality of resource elements

(RE1 , RE2,..., RE_K) based on computed power boosting probabilities for each resource element (REk) of the plurality of resource elements (RE1 , RE2,..., RE_K), and

c) compute a joint probability for the control channel symbol (s) based on the combined power boosting probability.

2. Estimator (100) according to claim 1 , wherein the processor (102) is configured to

d) compute a respective mean (z_k) of the estimate (q_k) for each resource element (REk) of the plurality of resource elements (RE1 , RE2,..., RE_K) based on the joint probability, e) subtract from the received communication signal (y) the computed mean (z_k) for each resource element (REk) so as to obtain a subtracted received communication signal,

f) compute a respective variance (e_k) for each resource element (REk) of the plurality of resource elements (RE1 , RE2,..., RE_K) based on the joint probability, and

g) filter the subtracted received communication signal with the computed variance (e_k) for each resource element (REk) so as to obtain the estimate (q_k) of the control channel symbol (s) at a) for each resource element (REk).

3. Estimator (100) according to claim 2, wherein the processor (102) is configured to

repeat a) to g) iteratively.

4. Estimator (100) according to claim 3, wherein the estimate (q_k) of the control channel symbol (s) and the associated variance (5 ) for each resource element (REk) at a) in a first iteration is obtained from MMSE estimation.

5. Estimator (100) according to claim 3 or 4, wherein the processor (102) is configured to stop the iterations when the combined power boosting probability in two consecutive iterations changes less than a threshold value.

6. Estimator (100) according to claim 5, wherein the processor (102) is configured to provide the estimate (q_k) of the control channel symbol (s) at g) as the final estimate for each resource element (REk).

7. Estimator (100) according to any of the preceding claims, wherein the processor (102) is configured to

compute the combined power boosting probability based on the product of the power boosting probability for each resource element (REk) of the plurality of resource elements (RE1 , RE2, ... , RE_K).

8. Estimator (100) according to claim 7, wherein the received communication signal (y) comprises a plurality of control channel symbols (s) of at least one serving cell,

wherein the processor (102) is configured to

compute the combined power boosting probability based on

where is tne product of the power boosting probabilities for all resource

elements of the plurality of resource elements given the estimated signal

q_iik , where i is the cell index and k is the resource element index.

9. Estimator (100) according to any of the preceding claims, wherein the processor (102) is configured to

10. Estimator (100) according to claim 9, wherein the received communication signal

comprises a plurality of control channel symbols (s) of at least one serving cell,

wherein the processor (102) is configured to compute the joint probability

based on

where is the

probability for the control channel symbol s_iik given the estimated signal

for cell i at resource element

1 1 . Estimator (100) according to any of the preceding claims, wherein the control channel symbol (s) is transmitted with the same power boosting value in the plurality of resource elements (RE1 , RE2,..., RE_K).

12. Receiving device for a wireless communication system (500), the receiving device (300) comprising

an estimator (100) according to any of the preceding claims, and

a receiver (302) configured to

receive the communication signal (y) in the wireless communication system (500), and provide the received communication signal (y) to the estimator (100).

13. Method (200) comprising:

obtaining (202) a received communication signal (y) comprising a control channel symbol (s) transmitted on a plurality of resource elements (RE1 , RE2,..., RE_K),

a) computing (204) a power boosting probability (p_fc) for each resource element (REk) of the plurality of resource elements (RE1 , RE2,..., RE_K) based on an estimate (q_k) of the control channel symbol (s) transmitted on the resource element (REk) and an associated variance (5 ),

b) computing (206) a combined power boosting probability for the plurality of resource elements (RE1 , RE2,..., RE_K) based on computed power boosting probabilities for each resource element (REk) of the plurality of resource elements (RE1 , RE2,..., RE_K),

c) computing (208) a joint probability for the control channel symbol (s) based on the combined power boosting probability.

14. Computer program with a program code for performing a method according to claim 13 when the computer program runs on a computer.