WO2019174743A1

WO2019174743A1 - Receiver and transmitter for multipath angle estimation

Info

Publication number: WO2019174743A1
Application number: PCT/EP2018/056687
Authority: WO
Inventors: Jian Luo; Mario Castaneda; Wolfgang Utschick; Christoph Stöckle
Original assignee: Huawei Technologies Co., Ltd.; Technische Universität München
Priority date: 2018-03-16
Filing date: 2018-03-16
Publication date: 2019-09-19
Also published as: CN112514277B; CN112514277A

Abstract

The present invention provides a receiving device and a transmitting device, which enable to carry out improved angle estimation (AE) of multiple path of a signal transmitted from the transmitting device to the receiving device. The AE can be integrated with Channel Estimation (CE), and can improve the quality of the CE and the ability of positioning of the receiving device by the transmitting device. The receiving device is configured to perform a first multipath angle estimation based on a first angular grid, obtain antenna characteristics of the transmitting device, obtain an oversampling factor, determine a second angular grid based on the oversampling factor and the first angular grid, and perform a second multipath angle estimation based on the first multipath angle estimation, the antenna characteristics, and the second angular grid. The transmitting device is configured to transmit antenna characteristics of an antenna array of the transmitting device to the receiving device, determine an oversampling factor for a first angular grid, and transmit the oversampling factor to the receiving device.

Description

RECEIVER AND TRANSMITTER FOR MULTIPATH ANGLE ESTIMATION

TECHNICAL FIELD

The present invention relates to a receiving device, particularly a receiver, and to a transmitting device, particularly a transmitter, for Angle Estimation (AE) of multiple path information of a signal (multipath AE). The receiving and transmitting device may form a system, in which information is shared e.g. about antenna characteristics of the transmitting device, in order to perform the multipath AE. The present invention relates also to a method for multiple path AE, e.g. performed at the receiver side, and to a method for supporting multipath AE, e.g. performed at the transmitter side.

BACKGROUND

Exploiting mm-wave frequencies is key for 5G to fulfill the extremely high required data rates. For mm-wave communications, the usage of a large number of antennas (in arrays) and a hybrid analog-digital beamforming architecture are the current assumption. Furthermore, irregular antenna arrays can be deployed to improve beam shapes and to reduce control circuits.

In addition to enabling the very high data rates, the large bandwidth at the mm-wave and the beamformed operation also facilitate enhanced radio based positioning, for which accurate AE is required. Multipath AE specifically enables the positioning of a Mobile Station (MS) even with a single Base Station (BS).

In mm-wave communications, due to the sparse multi-path components of the communication channel, AE can be integrated into Channel Estimation (CE), wherein the accuracy of the AE affects also the quality of Channel State Information (CSI), and thus precoding performance. By estimating the multipath angles and gains (complex valued), instead of performing classical Multiple Input Multiple Output (MIMO) CE, the overhead of training or pilot signals can be reduced, despite the large number of antennas. Further, such CE is compatible with the hybrid analog-digital beamforming architecture. However, conventional solutions provide only a limited accuracy of the multipath AE, and thus poor positioning and CE.

As an example, Compressive Sensing (CS) techniques have been exploited, wherein particularly Hierarchical Beam Scanning (HBS) or Exhaustive Beam Scanning (EBS) has been applied. The CS is, for instance, done via the Orthogonal Matching Pursuit (OMP) mechanism. By applying this OMP mechanism, the sparsity of the mm-wave channel is exploited, and the strong paths are iteratively searched. The drawback of this example, however, is the high training signal overhead, which scales linearly with the number of MS. Furthermore, the AE accuracy for this example is limited to a beam scanning grid. Thus, the CE accuracy is rather limited as well.

As another example, an enhancement method has been proposed based on the above HBS approach. At each stage, an Auxiliary Beam Pair (ABP) is sent for each (roughly) identified path direction of the channel. Each of these ABPs is slightly set to the left and right of the original beam and contains channel power. Such ABPs are used to refine the AE accuracy. The drawback of these ABPs, however, is their additionally required transmission, which results in extra overhead and latency. The higher the required accuracy of the AE, the more stages have to be performed, and the thinner the auxiliary beams need to be. Also the overhead becomes higher.

SUMMARY

In view of the above-mentioned disadvantages, the present invention aims to improve the conventional solutions. The present invention has the objective to provide a solution for higher accuracy AE multiple path information of a signal. In particular, the present invention intends to provide a receiving device and a transmitting device, respectively, for enabling the higher accuracy AE. Consequently, the present invention seeks to enhance both positioning and CE.

The objective of the present invention is achieved by the solution provided in the enclosed independent claims. Advantageous implementations of the present invention are further defined in the dependent claims. Three issues are taken into account for the solution to the objective of the present invention:

Firstly, constraints of the Hybrid Architecture (HA) on AE and CE is considered. This means that at the transmitting device an individual pilot sequence for each antenna is not possible. Instead, only an individual pilot sequence per Radio Frequency (RF) chain is possible. At the receiving device, an evaluation of the individual signals of each receiving antenna is not possible. Instead, only the signals at the output of each RF chain (which is a weighted sum of the signals of the receiving antennas) are available for evaluation.

Secondly, the general approach for CE (integrating AE) with a HA and performing beam scanning is assumed.

Thirdly, it is assumed that irregular arrays as well as regular arrays can be used at the transmitting device. With irregular arrays, high gains, better beam shapes, and a reduced number of controls can be achieved. With regular arrays, beam patterns can be easily calculated from the antenna geometry, which facilitates AE.

The main idea of the solution of the present invention is exploiting antenna characteristics of the transmitting device for achieving high resolution multiple path AE based on e.g. Downlink (DL) beam scanning. The high resolution multipath AE can be done, e.g., using a Multi-Dimensional extension of the Newtonized OMP (MD-NOMP).

A first aspect of the present invention provides a receiving device for angle estimation of multiple path information of a signal received from a transmitting device, the receiving device being configured to perform a first multipath angle estimation based on a first angular grid; obtain antenna characteristics of the transmitting device; obtain an oversampling factor; determine a second angular grid based on the oversampling factor and the first angular grid; and perform a second multipath angle estimation based on the first multipath angle estimation, the antenna characteristics, and the second angular grid.

Based on the received antenna characteristics and the determined second angular grid, which is particularly an oversampled angular grid regarding the first angular grid, the receiving device is able to perform improved AE, especially with a higher accuracy than in the conventional solutions. Further, by performing a two- stage AE, the computational complexity is kept low, and may especially be significantly lower than for pure OMP performed on a fine angular grid. Also the performance of the AE may be drastically improved compared to e.g. pure OMP solutions with comparable numerical complexity. Another advantage is that the receiver can perform the high accuracy AE for both regular and irregular antenna arrays of the transmitting device. As further advantages, higher quality CSI and thus improved CE is possible, since the AE may be integrated in the CE, and also improved positioning is enabled.

An“angular grid” may, for instance, comprised multiple angular sectors or intervals with the same mutual angular distance and equal angular width. Angular distance between two angular intervals can e.g. be measured from the respective centers of the angular widths. The finer the angular grid, the smaller the mutual angular distance and the smaller the angular width of each interval. The coarser the angular grid, the larger the mutual angular distance and the larger the angular width of each interval.

An“oversampling factor” is a factor that can be applied to (computed with, e.g. multiplied with) an angular grid to calculate a finer or coarse angular grid. For instance, if the value of the oversampling factor is above a certain threshold value, an angular grid may become a finer angular grid when the oversampling factor is applied. If the value of the oversampling factor is below the certain threshold value, the angular grid may become a coarser angular grid when the oversampling factor is applied, or vice versa. Further, it may be that the larger the value of the oversampling factor is (e.g. from the certain threshold value on), the finer the calculated angular grid may become.

“Antenna characteristics” comprise beam patterns and/or steering vectors, or comprise information that allows deriving beam patterns and/or steering vectors e.g. by calculation.

In an implementation form of the first aspect, the receiving device is configured to perform the second multipath angle estimation by using a CS technique.

Thereby, an accurate but efficient AE is carried out by the receiving device.

A“CS technique” is a known signal processing technique for efficiently acquiring and reconstructing a signal, by finding solutions to underdetermined linear systems. In a further implementation form of the first aspect, the receiving device is configured to perform the second multipath angle estimation by using an OMP mechanism, in particular a MD-NOMP mechanism.

With this mechanism, the multipath AE can be performed very accurately with at the same time low numerical complexity.

In a further implementation form of the first aspect, the receiving device is configured to determine an array response within an angular interval of the first angular grid from the antenna characteristics, and perform the second multipath angle estimation based on the array response.

By taking into account also one or more array responses (e.g. one or more array response vectors), it is possible to further improve the multipath AE performed by the receiving device.

In a further implementation form of the first aspect, the receiving device is configured to perform the first multipath angle estimation to obtain a subset of angular intervals of the first angular grid; obtain the antenna characteristics within the subset of angular intervals; and perform the second multipath angle estimation for the subset of angular intervals.

In this way, a high accuracy of the multipath AE paired with a low numerical complexity is possible. It is thereby also possible that the receiving device first sends a requirement to the transmitting device, in order to ask for antenna characteristics, and then obtains the antenna characteristics directly or indirectly from the transmitting device.

In a further implementation form of the first aspect, the receiving device is configured to perform the first multipath angle estimation by a beam scanning procedure or based on an OMP mechanism.

It is also possible to combine both techniques. In particular, an OMP mechanism may follow a beam scanning procedure for performing the first multipath AE. In a further implementation form of the first aspect, the receiving device is configured to feedback the second multipath angle estimation and/or the first multipath angle estimation to the transmitting device.

Thus, an improved CE feedback to the transmitting device can be implemented.

In a further implementation form of the first aspect, the receiving device is configured to feedback the second multipath angle estimation to the transmitting device as at least an angle and a complex gain of one or more of the multiple paths of the signal, in particular wherein an angle is determined by an index of the second angular grid.

In other words, the receiving device may feedback the estimated channel in terms of the angle and complex gain of each path. The angle may be particularly fed back in terms of the index of the (oversampled) second angular grid.

A second aspect of the present invention provides a transmitting device for supporting angle estimation of multiple path information of a signal transmitted to a receiving device, the transmitting device being configured to transmit antenna characteristics of an antenna array of the transmitting device to the receiving device; determine an oversampling factor for a first angular grid; and transmit the oversampling factor to the receiving device.

By transmitting the antenna characteristics and the oversampling factor to the receiving device, the transmitting device enables the receiving device to perform the higher accuracy AE described above with respect to the first aspect. Accordingly, the transmitting device supports the above-mentioned advantages and effects. The transmitting device can determine the oversampling factor based on the requirements, its capabilities and the network status, e.g. signaling overhead, and can thus guarantee a precise but efficient AE and CE feedback.

In an implementation form of the second aspect, the transmitting device is configured to transmit antenna characteristics for each angular interval of the first angular grid or for a subset of angular intervals of the first angular grid to the receiving device. In this way, the high accuracy and/or the low numerical complexity of the multipath AE at the receiving device is supported.

In a further implementation form of the second aspect, if the antenna array of the transmitting device is an irregular array, the antenna characteristics include beam patterns, steering vectors, and/or array responses within angular intervals of the first angular grid.

This implementation form allows the receiving device to perform the high accuracy AE with particularly low computational complexity for irregular antenna arrays of the transmitting device.

In a further implementation form of the second aspect, if the antenna array of the transmitting device is a regular array, the antenna characteristics include a type and/or geometry of the antenna array of the transmitting device.

This implementation form allows the receiving device to perform the high accuracy AE with particularly low computational complexity for regular antenna arrays of the transmitting device. From the type and/or geometry, beam patterns can be easily calculated at the receiving device.

In a further implementation form of the second aspect, the transmitting device is configured to determine the oversampling factor based on its precoder quantization level.

Thus, the transmitting device is able to select the best refinement of the angular grid at the receiving device, particularly depending on accuracy requirements, network status or the like.

In a further implementation form of the second aspect, the transmitting device is configured to determine the oversampling factor based on a requirement parameter and/or a signaling overhead.

Thus, the current requirements and the current overhead is taken into account, thereby enabling a more efficient AE feedback procedure. In a further implementation form of the second aspect, the transmitting device is configured to transmit one or more pilots with certain beam types in a subset of angular intervals to the receiving device, wherein the subset of angular intervals is determined based on a multipath angle estimation feedback received from the receiving device.

For instance, the transmitting device may transmit pilots or training signals with certain predefined beam types or beam types it agreed upon with the receiving device. Such beam types are typically different from those used in beam scanning.

A third aspect of the present invention provides a method for angle estimation of multiple path of a signal transmitted from a transmitting device to a receiving device, the method comprising performing a first multipath angle estimation based on a first angular grid; obtaining antenna characteristics of the transmitting device; obtaining an oversampling factor; determining a second angular grid based on the oversampling factor and the first angular grid; and performing a second multipath angle estimation based on the first multipath angle estimation, the antenna characteristics, and the second angular grid.

In an implementation form of the third aspect, the method comprises performing the second multipath angle estimation by using a CS technique.

In a further implementation form of the third aspect, the method comprises performing the second multipath angle estimation by using an OMP mechanism, in particular a MD- NOMP mechanism.

In a further implementation form of the third aspect, the method comprises determining an array response within an angular interval of the first angular grid from the antenna characteristics, and performing the second multipath angle estimation based on the array response.

In a further implementation form of the third aspect, the method comprises performing the first multipath angle estimation to obtain a subset of angular intervals of the first angular grid; obtaining the antenna characteristics within the subset of angular intervals; and performing the second multipath angle estimation for the subset of angular intervals. In a further implementation form of the third aspect, the method comprises performing the first multipath angle estimation by a beam scanning procedure or based on an OMP mechanism.

In a further implementation form of the third aspect, the method comprises feeding back the second multipath angle estimation and/or the first multipath angle estimation to the transmitting device.

In a further implementation form of the third aspect, the method comprises feeding back the second multipath angle estimation to the transmitting device as at least an angle and a complex gain of one or more of the multiple paths of the signal, in particular wherein an angle is determined by an index of the second angular grid.

The method of the third aspect and its implementation forms provide the same advantages and effects as described above for the receiving device of the first aspect and its respective implementation forms. That is, it supports a high accuracy AE with low numerical complexity and flexible use for different kinds of antenna arrays. Accordingly, also higher quality CSI can be obtained.

A fourth aspect of the present invention provides a method for supporting angle estimation of multiple path of a signal transmitted from a transmitting device to a receiving device, the method comprising transmitting antenna characteristics of an antenna array of the transmitting device to the receiving device; determining an oversampling factor for a first angular grid; and transmitting the oversampling factor to the receiving device.

In an implementation form of the fourth aspect, the method comprises transmitting antenna characteristics for each angular interval of the first angular grid or for a subset of angular intervals of the first angular grid to the receiving device.

In a further implementation form of the fourth aspect, if the antenna array of the transmitting device is an irregular array, the antenna characteristics include beam patterns, steering vectors, and/or array responses within angular intervals of the first angular grid. In a further implementation form of the fourth aspect, if the antenna array of the transmitting device is a regular array, the antenna characteristics include a type and/or geometry of the antenna array of the transmitting device.

In a further implementation form of the fourth aspect, the method comprises determining the oversampling factor based on its precoder quantization level.

In a further implementation form of the fourth aspect, the method comprises determining the oversampling factor based on a requirement parameter and/or a signaling overhead.

In a further implementation form of the fourth aspect, the method comprises transmitting one or more pilots with certain beam types in a subset of angular intervals to the receiving device, wherein the subset of angular intervals is determined based on a multipath angle estimation feedback received from the receiving device.

The method of the fourth aspect and its implementation forms provide the same advantages and effects as described above for the transmitting device of the second aspect and its respective implementation forms. That is, it supports a high accuracy AE with low numerical complexity and flexible use for different kinds of antenna arrays. Accordingly, also higher quality CSI can be obtained.

It has to be noted that all devices, elements, units and means described in the present application could be implemented in the software or hardware elements or any kind of combination thereof. All steps which are performed by the various entities described in the present application as well as the functionalities described to be performed by the various entities are intended to mean that the respective entity is adapted to or configured to perform the respective steps and functionalities.

Even if, in the following description of specific embodiments, a specific functionality or step to be performed by external entities is not reflected in the description of a specific detailed element of that entity which performs that specific step or functionality, it should be clear for a skilled person that these methods and functionalities can be implemented in respective software or hardware elements, or any kind of combination thereof. BRIEF DESCRIPTION OF DRAWINGS

The above described aspects and implementation forms of the present invention will be explained in the following description of specific embodiments in relation to the enclosed drawings, in which

FIG. 1 shows a receiving device according to an embodiment of the present invention.

FIG. 2 shows a transmitting device according to an embodiment of the present invention.

FIG. 3 shows an example of a beam scanning procedure.

FIG. 4 shows an example of a format of beam pattern feedback.

FIG. 5 shows an example illustration of a MD-NOMP procedure.

FIG. 6 shows a method according to an embodiment of the present invention.

FIG. 7 shows a method according to an embodiment of the present invention.

DETAIFED DESCRIPTION OF EMBODIMENTS FIG. 1 shows a receiving device 100 according to an embodiment of the present invention. The receiving device 100 is particularly configured to perform an AE of multiple path information of a signal 101 received from a transmitting device 110, i.e. in the DL. To this end, the receiving device 100 may be configured to implement several functions or steps, e.g. carried out by means of a processor of the receiving device 100.

In particular, the receiving device 100 is configured to perform a first multipath AE 102 based on a first angular grid 103. The first multipath AE 102 may, for example, be performed by a beam scanning procedure 300 (as e.g. shown in FIG. 3) and/or based on an OMP mechanism. The first angular grid 103 may be a predefined angular grid (regular angular grid) including a plurality of angular intervals. For example, as shown in FIG. 4 for five angular intervals 400, the multiple angular intervals 400 can have a certain mutual angular distance 401 (determined as the distance between the centers of two neighboring angular intervals 400) and certain equal angular widths 402.

The receiving device 100 is further configured to obtain antenna characteristics 104 of the transmitting device 110. For instance, these antenna characteristics 104 may be received directly or indirectly from the transmitting device 110. However, the receiving device 100 may also determine the antenna characteristics based on information received directly or indirectly from the transmitting device 110, or based on information derived from the received signal 101, or based on information obtained from another transmitting device.

Further, the receiving device 100 is configured to obtain an oversampling factor 105, and to determine a second angular grid 106 based on the oversampling factor 105 and the first angular grid 103. The second angular grid 106 may particularly be an oversampled angular grid calculated from the first angular grid 103 with the oversampling factor 105, i.e. is a finer angular grid than the first angular grid 103. The oversampling factor may be received directly or indirectly from the transmitting device 110, or may be determined otherwise.

Further, the receiving device 100 is configured to perform a second multipath AE 107 based on the first multipath AE 102, the antenna characteristics 104, and the second angular grid 106. In particular, the receiving device 100 may perform the second multipath AE 107 by using a CS technique, like an OMP mechanism, in particular a MD-NOMP mechanism 500 (as e.g. shown in FIG. 5).

FIG. 2 shows a transmitting device 200 according to an embodiment of the present invention. The transmitting device 200 is particularly configured to support AE of multiple path information of a signal 201 transmitted to a receiving device 210. The transmitting device 200 may be the transmitting device 110 shown in FIG. 1 and/or the receiving device 210 may be the receiving device 100 shown in FIG. 1 (i.e. wherever in the following reference sign 210 is used, also 100 could be used, and vice versa). The transmitting device 200 and the receiving device 100 shown in the FIGs. 1 and 2 may accordingly form a system according to an embodiment of the present invention. The transmitting device 200 is configured to transmit antenna characteristics 204 of an antenna array 202 of the transmitting device 200 to the receiving device 210. If the antenna array 202 of the transmitting device 200 is an irregular antenna array, the antenna characteristics may include beam patterns, steering vectors, and/or array responses (e.g. array response vectors) within angular intervals 400 of the first angular grid 103. If the antenna array 202 of the transmitting device 200 is a regular antenna array, the antenna characteristics 204 may include a type and/or geometry of the antenna array 202 of the transmitting device 200.

Further, the transmitting device 200 is configured to determine an oversampling factor 205 for a first angular grid 203. This oversampling factor 205 may be identical to the oversampling factor 105 for the first angular grid 103 mentioned above (i.e. wherever in the following reference sign 203 or 205 is used, also 103 or 105 could be used, and vice versa). For instance, the transmitting device 200 may determine the oversampling factor 205 based on its precoder quantization level and/or based on a requirement parameter and/or based on a signaling overhead.

Further, the transmitting device 200 is configured to transmit at least the oversampling factor 205 to the receiving device 210.

For the above receiving device 100 and transmitting device 200 according to embodiments of the present invention, the AE (integrated into CE) is assumed to be done in the DL. A common beam code book may be predefined, which may span a respective channel subspace. One example for such a common beam code book is the Discrete Fourier Transform (DFT) beam code book.

In the following, the specific enhancements provided to the receiving device 100 and transmitting device 200 according to the above-mentioned embodiments of the present invention are described in more detail.

The transmitting device 200, e.g. a BS, may signal to the receiving device 100, e.g. a MS, specifically the following information: • Whether its antenna array 202 is an irregular array.

• In case its antenna array 202 is an irregular array, beam patterns of certain beams for angular intervals 400 containing strong multipath components, with a certain angular sampling resolution (according to the first angular grid 103).

• In case its antenna array 202 is not an irregular array, the type of the given regular array structure (e.g. a Uniform Linear Array (ULA) or a Uniform Rectangular Array (URA)), and geometry information for the array 202 (e.g. a number of antenna elements along each dimension of the array 202, antenna element spacing etc.).

The high resolution multipath AE is then performed according to a two- stage procedure specifically as follows.

Stage 1: After the transmitting device 200 indicated whether it has an irregular/regular array 202, the transmitting device 200 performs beam scanning 300, and the receiving device 100 performs a beam alignment procedure (e.g. as in IEEE 802.1 lad) or performs a standard OMP (e.g. by assuming the used beam patterns at the transmitting device 200), in order to obtain a subset of angular intervals 400 with substantial channel contributions.

For performing the beam scanning 300, as e.g. shown in FIG. 3, pilots may be transmitted and received over pairs of transmitter beams and receiver beams, respectively. Afterwards, the received pilots of all beam pairs may be stored at the receiving device 100. From the received pilots, the receiving device 100 may calculate the first multipath AE 102, e.g. by weighting and combining the received pilots or just comparing the received power of each beam pair.

In this stage 1, the receiving device 100 particularly uses the first angular grid 103, which is rougher compared to the second angular grid 106 (e.g. a regular grid based on the angular resolution of the beam codebook) to get the first multipath AE 102 (lower resolution AE).

• Stage 2: The transmitting device 200 may send beam patterns (which were used in the beam scanning 300) in a subset of angular intervals 400 (as mentioned in stage 1). After obtaining these beam patterns, the receiving device 100 may perform higher resolution AE, i.e. the second multipath AE 107, e.g., by using the MD-NOMP algorithm 500. When the MD-NOMP algorithm 500 is used, the receiving device 100 may specifically calculate the first and second derivatives of the steering vectors of the transmitting device 200, based on the antenna geometry (regular structure) or the beam patterns (non-regular structure).

In other words, based on the lower resolution first multipath AE 102, the receiving device 100 is configured to apply a CS technique (e.g. the MD-NOMP 500) to implement the higher resolution second multipath AE, in order to enhance overall AE and CE accuracy. From the OMP, the complex gain and angle of each channel path/cluster may be estimated.

In this stage 2, the receiving device 100 particularly uses the finer second angular grid 106 to get the second multipath AE 107. To this end, the transmitting device 200 also signals to the receiving device 100 the oversampling factor 105/205. “Oversampling” refers to the refinement of the first angular grid 103/203. The oversampling factor 105/205 may be determined by the transmitting device 200 based on its precoder quantization level, the application requirement (e.g., positioning accuracy, data rate) and/or signaling overhead. Notably, the transmitting device 200 may determine different oversampling factors 105/205 for different receiving devices 100 (in case that the transmitting device 200 communicates with multiple receiving devices 100). Accordingly, the transmitting device 200 signals the determined oversampling factors 105/205 respectively to each receiving device 100.

Optionally, the transmitting device 200 may also provide the receiving device 100 with transmit beams corresponding to the communicated beam patterns (or beam patterns corresponding to the regular array structure) into the above-mentioned subsets, if such beam patterns are different from those used in the beam scanning procedure 300. The receiving device 100 may then performs the above mentioned high resolution multipath AE 107, e.g., using the MD-NOMP algorithm 500.

Finally, after performing the estimation, one or more receiving devices 100 feedback the estimated channel in terms of the angle and complex gain of each path to the transmitting device 200. The angle is particularly fed back in terms of the index of the oversampled angular grid. For instance, the receiving device 100 may send the estimated angles in terms of the oversampled grid point (as well as complex gain/impulse response of that angle) to the transmitting device 200. The signaling format may consist of the index on the regular first angular grid 103, and the shift from the center of the regular angular grid interval in terms of the number of oversampled grid points.

In the following, specific implementations regarding the above-described enhancements are described with respect to the transmitting device 200 and receiving device 100 according to embodiments of the present invention.

In an implementation for the case of an irregular antenna array structure used at the transmitting device 200, a two-stage signaling approach of the antenna characteristic information may be used to reduce overhead. The transmitting device 200 may signal to the receiving device 100 only the detailed antenna characteristic information for a subset of angular intervals 400 (of the regular angular grid 103), where this subset contains the main channel power. The two-stage signaling approach may consist of the following steps:

• Step 1: The transmitting device 200 may obtains information about this subset (e.g., angle/beam index) via one of the following options:

Option 1: The receiving device 100 can measure the received power of each beam pair and feedback the strongest beam identifiers (ID).

Option 2: A rough Angle of Departure (AoD) estimation can be performed at a lower frequency.

Option 3: Such information can be extracted from previous channel estimates.

• Step 2: The transmitting device 200 may inform the receiving device 100 about this subset (if the receiving device 100 does not know about it).

• Step 3: The receiving device 100 may feedback for which angular intervals 400 (index on the regular first angular grid 103) it exactly needs the antenna characteristic information. Note that the receiving device 100 may already have such information for some angular intervals 400 from a previous CE procedure. • Step 4: The transmitting device 200 may send the required information to the receiving device 100. The corresponding content of such information will be shown later. The feedback of beam patterns of irregular arrays can specifically have the following examples:

Example 1 : Beam pattern, steering vectors or array response (vectors) in each of the angular intervals 400 of the first angular grid 103, as shown in FIG. 4. The beam pattern can be sampled based on the oversampled second angular grid 106.

Example 2: First and second derivative of steering vector for angular estimation in each angular interval 400 of the first angular grid 103.

• Step 5: The receiving device 100 performs (e.g.) the MD-NOMP algorithm 500 to calculate the channel estimate and feeds back improved angular estimates (e.g. offset from regular first angular grid 103, offset in terms of oversampled angular grid 106) and the complex channel gains.

Each angular interval 400 has a center angle. All angular intervals 400 may thereby have the same length. However, the lengths of the intervals 400 can also differ. Further, the whole angular range may be equally divided into n intervals 400.

However, such an equal division of the angular range is only a typical example, and also other divisions of the angular range are allowed. The following shows an example of an angular interval 400

on the first angular grid 103 at the BS

1,2, ... , G_BS

In a further implementation, the MD-NOMP algorithm 500 described above and shown in FIG. 5 is a straightforward MD-extension of the Newtonized OMP (MD-NOMP). First, in the i^th OMP-iteration, the receiving device 100 performs Newton Iterations to maximize the Marginal Likelihood

Separately for every path l = 1, ... , i and every angle 0_; ^BS, 0_; ^MS with path gain bi, residual r_t for path l and a(0f^s, 0i^MS) = «_Bs(0p^S) ® ^a _Ms(0i^MS)· Subsequently, the receiving device 100 refines the coarse on-grid angle estimates found in each OMP-iteration. For instance, an example pseudo-code of the MD-NOMP algorithm 500 is illustrated below (wherein BS denotes the transmitting device 200, and MS the receiving device 100)

for n = t, ...,N do

end

In a further implementation, the transmitting device 200 may transmit additional pilots in the above-described stage 2, wherein such pilots are particularly sent in a subset of directions. The subset of directions is determined by an initial CE at the receiving device 100. An example of such pilots is the off-center (center refers to the center angle of an interval on the regular grid) beams on the second angular grid 106, for calculating the derivatives of beam patterns. The advantage of this variation is an improved SNR of the residual signal for the OMP processing.

A further implementation concerns the determination of the oversampling factor 205 at the transmitting device 200. A set of allowable oversampling factors 205 may be predefined. The transmitting device 200 may select an oversampling factor 205 based on its precoder quantization level, the application requirement (e.g. data transmission or positioning) and the signaling overhead. Different receiving devices 100 can have different oversampling factors 205. The oversampling factor 205 depends on the signaling overhead (e.g., about beam patterns). The transmitting device 200 may signal this oversampling factor 205 to each receiving device 100 (the oversampling factor refers to a first angular grid 103).

FIG. 6 shows a method 600 according to an embodiment of the present invention. The method 600 is usable for AE of multiple path of a signal 101 transmitted from a transmitting device 110 to a receiving device 100. Accordingly, the method 600 may be carried out by a receiving device 100 according to an embodiment of the present invention, for example, as shown in FIG. 1.

The method 600 includes a step 601 of performing a first multipath AE 102 based on a first angular grid 103. A step 602 of obtaining antenna characteristics 104 of the transmitting device 110. A step 603 of obtaining an oversampling factor 105. A step 604 of determining a second angular grid 106 based on the oversampling factor 105 and the first angular grid 103. A step 605 of performing a second multipath AE 107 based on the first multipath AE 102, the antenna characteristics 104, and the second angular grid 106.

FIG. 7 shows a method 700 according to an embodiment of the present invention. The method 700 is usable for supporting AE of multiple path of a signal 201 transmitted from a transmitting device 200 to a receiving device 210. Accordingly, the method 700 may be carried out by a transmitting device 200 according to an embodiment of the present invention, for example, as shown in FIG. 2.

The method 700 includes a step 701 of transmitting antenna characteristics 204 of an antenna array 202 of the transmitting device 200 to the receiving device 210. A step 702 of determining an oversampling factor 205 for a first angular grid 203. A step 703 of transmitting the oversampling factor 205 to the receiving device 210. In summary, the present invention has the following advantages:

• Enhanced multipath AE and thus improved positioning accuracy and CE quality.

• Much lower computational complexity than pure OMP that uses finer angular grids for improving AEs.

• Drastically improved performance over pure OMP solutions with comparable numerical complexity.

The present invention has been described in conjunction with various embodiments as examples as well as implementations. However, other variations can be understood and effected by those persons skilled in the art and practicing the claimed invention, from the studies of the drawings, this disclosure and the independent claims. In the claims as well as in the description the word“comprising” does not exclude other elements or steps and the indefinite article“a” or“an” does not exclude a plurality. A single element or other unit may fulfill the functions of several entities or items recited in the claims. The mere fact that certain measures are recited in the mutual different dependent claims does not indicate that a combination of these measures cannot be used in an advantageous implementation.

Claims

1. Receiving device ( 100) for angle estimation of multiple path information of a signal (101) received from a transmitting device (110), the receiving device (100) being configured to

- perform a first multipath angle estimation (102) based on a first angular grid (103);

- obtain antenna characteristics (104) of the transmitting device (110);

- obtain an oversampling factor (105);

- determine a second angular grid (106) based on the oversampling factor (105) and the first angular grid (103); and

- perform a second multipath angle estimation (107) based on the first multipath angle estimation (102), the antenna characteristics (104), and the second angular grid (106).

2. Receiving device (100) according to claim 1, configured to

- perform the second multipath angle estimation (107) by using a Compressive Sensing, CS, technique.

3. Receiving device (100) according to claim 1 or 2, configured to

- perform the second multipath angle estimation (107) by using an Orthogonal Matching Pursuit, OMP, mechanism (500), in particular a Multi-Dimension Newtonized OMP, MD-NOMP, mechanism.

4. Receiving device (100) according to one of the claims 1 to 3, configured to

- determine an array response within an angular interval (400) of the first angular grid (103) from the antenna characteristics (104), and

- perform the second multipath angle estimation (107) based on the array response.

5. Receiving device (100) according to one of the claims 1 to 4, configured to

- perform the first multipath angle estimation (102) to obtain a subset of angular intervals (400) of the first angular grid (103);

- obtain the antenna characteristics (104) within the subset of angular intervals (400); and

- perform the second multipath angle estimation (107) for the subset of angular intervals (400).

6. Receiving device (100) according to one of the claims 1 to 5, configured to

- perform the first multipath angle estimation (102) by a beam scanning procedure (300) or based on an OMP mechanism (500).

7. Receiving device (100) according to one of the claims 1 to 6, configured to

- feedback the second multipath angle estimation (107) and/or the first multipath angle estimation (102) to the transmitting device (110).

8. Receiving device (100) according to one of the claims 1 to 7, configured to

- feedback the second multipath angle estimation (107) to the transmitting device (110) as at least an angle and a complex gain of one or more of the multiple paths of the signal (101), in particular wherein an angle is determined by an index of the second angular grid (106).

9. Transmitting device (200) for supporting angle estimation of multiple path information of a signal (201) transmitted to a receiving device (210), the transmitting device (200) being configured to

- transmit antenna characteristics (204) of an antenna array (202) of the transmitting device (200) to the receiving device (210);

- determine an oversampling factor (205) for a first angular grid (203); and

- transmit the oversampling factor (205) to the receiving device (210).

10. Transmitting device (200) according to claim 9, configured to

- transmit antenna characteristics (204) for each angular interval (400) of the first angular grid (203) or for a subset of angular intervals (400) of the first angular grid (203) to the receiving device (210).

11. Transmitting device (200) according to claim 9 or 10, wherein, if the antenna array (202) of the transmitting device (200) is an irregular array,

the antenna characteristics (204) include beam patterns, steering vectors, and/or array responses within angular intervals (400) of the first angular grid (203).

12. Transmitting device (200) according to claim 9 or 10, wherein, if the antenna array (202) of the transmitting device (200) is a regular array,

the antenna characteristics (204) include a type and/or geometry of the antenna array (202) of the transmitting device (200).

13. Transmitting device (200) according to one of the claims 9 to 12, configured to

- determine the oversampling factor (205) based on its precoder quantization level.

14. Transmitting device (200) according to one of the claims 9 to 13, configured to

- determine the oversampling factor (205) based on a requirement parameter and/or a signaling overhead.

15. Transmitting device (200) according to one of the claims 9 to 14, configured to

- transmit one or more pilots with certain beam types in a subset of angular intervals (400) to the receiving device (210), wherein the subset of angular intervals (400) is determined based on a multipath angle estimation feedback received from the receiving device (210).

16. Method (600) for angle estimation of multiple path of a signal (101) transmitted from a transmitting device (110) to a receiving device (100), the method (600) comprising performing (601) a first multipath angle estimation (102) based on a first angular grid (103);

obtaining (602) antenna characteristics (104) of the transmitting device (110); obtaining (603) an oversampling factor (105);

determining (604) a second angular grid (106) based on the oversampling factor (105) and the first angular grid (103); and

performing (605) a second multipath angle estimation (107) based on the first multipath angle estimation (102), the antenna characteristics (104), and the second angular grid (106).

17. Method (700) for supporting angle estimation of multiple path of a signal (201) transmitted from a transmitting device (200) to a receiving device (210), the method (700) comprising transmitting (701) antenna characteristics (204) of an antenna array (202) of the transmitting device (200) to the receiving device (210);

determining (702) an oversampling factor (205) for a first angular grid (203); and transmitting (703) the oversampling factor (205) to the receiving device (210).