阅读说明：本技术 用于处理上行链路信号的方法和装置 (Method and apparatus for processing uplink signals ) 是由 吕晨光 黄叶子 M.伯格 于 2017-06-14 设计创作，主要内容包括：提供了用于处理上行链路信号的机制。一种方法由RRU(200)执行。该方法包括获得在RRU(200)的天线阵列的天线元件处从无线装置所接收的上行链路信号(S102),每个无线装置与它自己的至少一个用户层相关联。该方法包括通过对于每个用户层将从天线阵列所接收的上行链路信号组合成组合信号,每用户层得到一个组合信号,来捕获(S104)每用户层的能量。对于每个单独用户层的组合基于与所述每个单独用户层相关联的无线装置的信道系数。该方法包括将组合信号提供(S106)给BBU(300)。(A mechanism is provided for processing uplink signals. methods are performed by an RRU (200). The method includes obtaining uplink signals received from wireless devices at antenna elements of an antenna array of the RRU (200) (S102), each wireless device associated with at least user layers of its own.A method includes capturing (S104) energy per user layer by combining, for each user layer, the uplink signals received from the antenna array into a combined signal, the resulting combined signal per user layer.)

1, a method for processing an uplink signal, the method being performed by a remote radio unit, RRU, (200), the method comprising:

obtaining (S102) uplink signals received at antenna elements of an antenna array of the RRU (200) from wireless devices, each wireless device being associated with at least user layers of its own;

capturing (S104) energy per user layer by combining the uplink signals received from the antenna array into a combined signal for each user layer, the combined signal resulting in combined signals per user layer, wherein the combining for each individual user layer is based on channel coefficients of the wireless device associated with said each individual user layer, and

providing (S106) the combined signal to a baseband unit, BBU, (300).

2. The method according to claim 1, wherein the received uplink signals are combined using maximal ratio combining and/or interference suppression combining.

3. The method of claim 1 or 2, wherein the channel coefficients relate to at least channel characteristics of a radio propagation channel extending between the wireless device of the each individual user layer and the antenna array of the RRU (200) in a direction from the wireless device to the antenna array.

4. The method of any of the preceding claim, wherein combining coefficients are applied to the uplink signals in order to combine the received uplink signals, and wherein the combining coefficients are based on the channel coefficients for each user layer.

5. The method of claim 4, wherein the combining coefficients are determined per antenna element or per direction in which the uplink signal is received at the antenna element.

6. The method according to claim 4 or 5, wherein the combining coefficients are applied to each antenna element or to the uplink signal for each direction in which the uplink signal is received at the antenna element.

7. The method according to claim 6, wherein the uplink signals of an antenna element are transformed into uplink signals of each direction before applying the combining coefficients to the uplink signals of each direction.

8. The method of claim 5, wherein the combining coefficients determined per direction are transformed into combining coefficients per antenna element.

9. The method of any of the preceding claim, wherein the uplink signal includes a reference signal, and wherein the reference signal is extracted when the energy is captured.

10. The method of any in the preceding claim, wherein the received signal in each user layer includes independently scheduled information.

11. The method of any of the preceding claims, further comprising:

selecting (S104 a) to combine, for each user layer, the received uplink signals from less than all of the antenna elements into the combined signal.

12. The method of claim 11, wherein for each user layer, uplink signals received from at least as many antenna elements as the total number of user layers are combined into the combined signal.

13. The method of claim 5, further comprising:

selecting (S104 b) to combine uplink signals received from less than all directions into the combined signal for each user layer when applying the combining coefficients for the uplink signals for each direction.

14. The method of claim 13, wherein for each user layer, uplink signals received from at least as many directions as the total number of user layers are combined into the combined signal.

15. The method of claim 3 in combination with any of claims 11-14, wherein the determination of which less than all of the antenna elements or directions to combine the received uplink signals from is based on the channel coefficients.

16. The method of any of the preceding claim, wherein for each polarization direction of the antenna elements, the received uplink signals are combined into separate combined signals.

17, method for processing uplink signals, the method being performed by a baseband unit, BBU, (300), the method comprising:

obtaining (S202) combined signals from a remote radio unit, RRU, (200), wherein each combined signal represents a combination of uplink signals received from wireless devices at antenna elements of an antenna array of the RRU (200), each wireless device being associated with at least user layers of its own;

performing (S204) interference cancellation on each of the combined signals, resulting in a combined signal after interference cancellation; and

separating (S206) the interference cancelled combined signal into separate uplink signals for each user layer such that there are separate user layers for each separate uplink signal.

18. The method of claim 17, wherein the interference is cancelled using linear cancellation such as zero-forcing interference cancellation or minimum mean square error interference cancellation or non-linear cancellation such as successive interference cancellation.

19. The method of claim 17 or 18, wherein the combined signal represents the uplink signal combined from less than all of the antenna elements.

20. The method of any of claims 17-19, wherein the combined signal represents the uplink signal combined from less than all directions in which the uplink signal is received at the antenna element.

21, a method for processing uplink signals, the method comprising:

obtaining (S102), by a remote radio unit, RRU, (200) uplink signals received from wireless devices at antenna elements of an antenna array of the RRU (200), each wireless device being associated with at least user layers of its own;

capturing (S104), by the RRU (200), energy per user layer by combining the uplink signals received from the antenna array into a combined signal for each user layer, resulting in combined signals per user layer, wherein the combining for each individual user layer is based on channel coefficients of the wireless device associated with said each individual user layer;

providing (S106), by the RRU (200), the combined signal to a baseband unit, BBU, (300);

obtaining (S202), by the BBU (300), the combined signal from the RRU (200);

performing (S204), by the BBU (300), interference cancellation on each of the combined signals, resulting in a combined signal after interference cancellation; and

separating (S206), by the BBU (300), the interference cancelled combined signal into separate uplink signals for each user layer, such that there are separate user layers for each separate uplink signal.

22, a remote radio unit, RRU, (200) for processing an uplink signal, the RRU (200) comprising processing circuitry (210) configured to cause the RRU (200) to:

obtaining uplink signals received at antenna elements of an antenna array of the RRU (200) from wireless devices, each wireless device being associated with at least user layers of its own;

capturing energy per user layer by combining the uplink signals received from the antenna array into a combined signal for each user layer, the combined signal being derived per user layer, wherein the combining for each individual user layer is based on channel coefficients of the wireless device associated with the each individual user layer, and

providing the combined signal to a baseband unit, BBU, (300).

23, a remote radio unit, RRU, (200) for processing uplink signals, the RRU (200) comprising:

an obtaining module (210 a), the obtaining module (210 a) configured to obtain uplink signals received at antenna elements of an antenna array of the RRU (200) from wireless devices, each wireless device being associated with at least user layers of its own;

an acquisition module (210 b), the acquisition module (210 b) configured to acquire energy per user layer by combining the uplink signals received from the antenna array into a combined signal for each user layer, the combined signal resulting in combined signals per user layer, wherein the combining for each individual user layer is based on channel coefficients of the wireless device associated with the each individual user layer, and

a providing module (210 e), the providing module (210 e) being configured to provide the combined signal to a baseband unit, BBU, (300).

24, , a baseband unit, BBU, (300) for processing uplink signals, the BBU (300) comprising processing circuitry (310) configured to cause the BBU (300) to:

obtaining combined signals from a remote radio unit, RRU, (200), wherein each combined signal represents a combination of uplink signals received from wireless devices at antenna elements of an antenna array of the RRU (200), each wireless device being associated with at least user layers of its own;

performing interference cancellation on each combined signal in the combined signals to obtain combined signals after the interference cancellation; and

separating the interference cancelled combined signal into separate uplink signals for each user layer such that there are separate user layers for each separate uplink signal.

25, , a baseband unit, BBU, (300) for processing uplink signals, the BBU (300) comprising:

an obtaining module (310 a), the obtaining module (310 a) configured to obtain combined signals from a remote radio unit, RRU, (200), wherein each combined signal represents a combination of uplink signals received from wireless devices at antenna elements of an antenna array of the RRU (200), each wireless device being associated with at least user layers of its own;

an interference cancellation module (310 b), the interference cancellation module (310 b) configured to perform interference cancellation on each of the combined signals, resulting in an interference cancelled combined signal; and

a separation module (310 c), the separation module (310 c) configured to separate the interference cancelled combined signal into separate uplink signals for each user layer such that there are separate user layers for each separate uplink signal.

26, access nodes (400), comprising at least RRUs (200) according to claim 22 or 23 and BBUs (300) according to claim 24 or 25.

27, a computer program (1420 a) for processing an uplink signal, the computer program comprising computer code which, when run on processing circuitry (210) of a remote radio unit, RRU (200), causes the RRU (200) to:

obtaining (S102) uplink signals received at antenna elements of an antenna array of the RRU (200) from wireless devices, each wireless device being associated with at least user layers of its own;

capturing (S104) energy per user layer by combining the uplink signals received from the antenna array into a combined signal for each user layer, the combined signal resulting in combined signals per user layer, wherein the combining for each individual user layer is based on channel coefficients of the wireless device associated with said each individual user layer, and

providing (S106) the combined signal to a baseband unit, BBU, (300).

28, , a computer program (1420 b) for processing uplink signals, the computer program comprising computer code which, when run on processing circuitry (310) of a baseband unit, BBU, (300), causes the BBU (300) to:

obtaining (S202) combined signals from a remote radio unit, RRU, (200), wherein each combined signal represents a combination of uplink signals received from wireless devices at antenna elements of an antenna array of the RRU (200), each wireless device being associated with at least user layers of its own;

performing (S204) interference cancellation on each of the combined signals, resulting in a combined signal after interference cancellation; and

separating (S206) the interference cancelled combined signal into separate uplink signals for each user layer such that there are separate user layers for each separate uplink signal.

29, computer program product (1410 a, 1410 b) comprising a computer program (1420 a, 1420 b) according to at least of claims 27 and 28 and a computer readable storage medium (1430), the computer program being stored on the computer readable storage medium (1430).

Technical Field

Embodiments presented herein relate to a method, a remote radio unit, a baseband unit, an access node, a computer program and a computer program product for processing uplink signals.

Background

In a communication network, it may be challenging to obtain good performance and capacity for a given communication protocol, its parameters, and the physical environment in which the communication network is deployed.

For example, the introduction of a digital beam forming antenna system in an access node, such as a radio base station, may allow multiple synchronized narrow beams to be used to provide network access, and thus a server, for multiple synchronized served wireless devices, such as User Equipments (UEs).

For example, in order to improve spectral efficiency to meet the requirements of fifth generation (5G) telecommunication systems, so-called massive Multiple Input Multiple Output (MIMO) systems have been proposed, massive MIMO systems can be used with a large number of antennas on the network side, where the number of antennas is much higher than the number of user layers, e.g., 64 antennas with 8 or 16 user layers.

Massive MIMO is commonly referred to as massive beamforming, where beamforming involves generating narrow beams pointing in different directions. Massive MIMO benefits primarily from multi-user MIMO, which enables simultaneous transmission to and reception from multiple users on separate spatial channels.

Traditionally, the functionality of an access node on the network side has been split between a baseband unit (BBU) and at least Remote Radio Units (RRUs) interconnected by a Fronthaul (FH) interface, resulting in a so-called master-remote design, in such a master-remote design, time domain samples of each antenna-carrier are transported over the FH interface.

some baseband PHY layer functions can be transferred from the BBU to the RRU in extreme cases, the main-remote design may be disrupted by removing the FH interface completely and putting the functionality of the BBU in the RRU, generally speaking, in this case, the RRU becomes the base station.

However, computational operations in massive MIMO are processing intensive and typically need to be performed in real time. The more such complex operations are transferred to the RRU, the more complex the RRU has to be designed.

In view of the above, there is still a need for an improved BBU-RRU arrangement.

Disclosure of Invention

It is an object of embodiments herein to provide efficient processing of uplink signals that can be used to improve the performance of BBU-RRU arrangements.

According to a th aspect, a method for processing uplink signals is presented . the method includes obtaining, by the RRU, uplink signals received from the wireless devices at antenna elements of an antenna array of the RRU, each wireless device associated with at least user layers of its own.

According to a second aspect, methods are presented for processing uplink signals, the method being performed by an RRU, the method comprising obtaining uplink signals received from wireless devices at antenna elements of an antenna array of the RRU, each wireless device being associated with at least user layers of its own.

According to a third aspect, RRUs for processing uplink signals are presented, the RRUs comprising processing circuitry, the processing circuitry configured to cause the RRUs to obtain uplink signals received from a wireless device at antenna elements of an antenna array of the RRUs, each wireless device being associated with at least user layers of its own, the processing circuitry configured to cause the RRUs to capture energy per user layer by combining the uplink signals received from the antenna array into a combined signal for each user layer, the combined signal being derived per user layer.

According to a fourth aspect, RRUs for processing uplink signals are proposed, the RRU comprising an obtaining module configured to obtain uplink signals received from wireless devices at antenna elements of an antenna array of the RRU, each wireless device being associated with at least user layers of its own, the RRU comprising an acquisition module configured to acquire energy per user layer by combining the uplink signals received from the antenna array into a combined signal for each user layer, the combined signal being derived per user layer the combining for each individual user layer being based on channel coefficients of the wireless devices associated with said each individual user layer.

According to a fifth aspect, a computer program for processing an uplink signal is presented, the computer program comprising computer code which, when run on processing circuitry of an RRU, causes the RRU to perform a method according to the second aspect.

The method includes performing interference cancellation on each combined signal in the combined signals, resulting in interference cancelled combined signals, separating the interference cancelled combined signals into separate uplink signals for each user layer, such that there are separate user layers for each separate uplink signal.

According to a seventh aspect, BBUs are proposed for processing uplink signals, the BBUs comprising processing circuitry configured to cause the BBUs to obtain combined signals from the RRUs, each combined signal representing a combination of uplink signals received from wireless devices at antenna elements of an antenna array of the RRUs, each wireless device being associated with at least user layers of its own.

According to an eighth aspect, BBUs for processing uplink signals are presented, the BBUs comprising an obtaining module configured to obtain combined signals from the RRUs, each combined signal representing a combination of uplink signals received from wireless devices at antenna elements of an antenna array of the RRUs, each wireless device being associated with at least user layers of its own, the BBUs comprising an interference cancellation module configured to perform interference cancellation on each of the combined signals, resulting in an interference cancelled combined signal, the BBU comprising a separation module configured to separate the interference cancelled combined signal into separate uplink signals for each user layer, such that there are separate user layers for each separate uplink signal.

According to a ninth aspect, a computer program for processing uplink signals is presented, the computer program comprising computer program code which, when run on processing circuitry of a BBU, causes the BBU to perform the method according to the sixth aspect.

According to a tenth aspect, computer program products are proposed, the computer program products comprising a computer program according to at least of the fifth and ninth aspects and a computer readable storage medium on which the computer program is stored.

According to a tenth aspect, access nodes are proposed, which access nodes comprise at least RRUs according to the third or fourth aspect and BBUs according to the seventh or eighth aspect.

Advantageously, the methods, the RRUs, the BBUs, the access node and the computer programs provide efficient processing of uplink signals that can be used to improve the performance of a BBU-RRU arrangement comprising the proposed BBUs and RRUs.

Advantageously, the methods, the RRUs, the BBUs, the access node and the computer programs enable high performance to be achieved at the air interface of the RRUs, while keeping the complexity in the RRUs low and reducing the capacity of the interface between the BBUs and the RRUs to match the number of user layers.

Advantageously, the methods, the RRUs, the BBUs, the access node and the computer programs are scalable and support a large number of antennas, e.g. enabling more RRUs to connect to the same BBUs and increase BBU capacity without replacing the RRU with a new RRU.

Advantageously, the methods, the RRUs, the BBUs, the access node and the computer programs enable a reduction of computational complexity requirements in the RRUs by combining only a subset of the antennas or directions.

Advantageously, the methods, the RRUs, the BBUs, the access node and the computer programs enable advanced channel estimation methods, such as successive interference cancellation, to be applied in the BBU to further improve the performance at step .

Advantageously, the methods, the RRUs, the BBUs, the access node and the computer programs may be applied to an active distributed antenna system, such as a radio point system (RDS), and improve the performance of such a system.

Other objects, features and advantages of the appended embodiments will be apparent from the following detailed disclosure, from the appended dependent claims and from the drawings.

in general, all terms used in the claims are to be interpreted according to their ordinary meaning in the art unless explicitly stated otherwise herein, all references to "//this element, device, assembly, component, module, step, etc" are to be interpreted openly as referring to at least instances of the element, device, assembly, component, module, step, etc., unless explicitly stated otherwise, the steps of any method disclosed herein are not to be performed in the exact order disclosed by unless explicitly stated otherwise.

Drawings

The inventive concept will now be described, by way of example, with reference to the accompanying drawings, in which:

fig. 1 and 2 are block diagrams of BBU-RRU arrangements;

fig. 3 and 4 are flow diagrams of methods according to embodiments;

fig. 5 is a schematic diagram of an access node according to an embodiment;

fig. 6, 7, 8 and 9 show simulation results according to an embodiment;

fig. 10 is a schematic diagram illustrating functional units of an RRU according to an embodiment;

fig. 11 is a schematic diagram illustrating functional modules of an RRU according to an embodiment;

FIG. 12 is a schematic diagram illustrating functional units of a BBU, according to an embodiment;

FIG. 13 is a schematic diagram that illustrates functional modules of a BBU, according to an embodiment; and

fig. 14 shows examples of a computer program product comprising computer readable means according to an embodiment.

Detailed Description

The present inventive concept will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments of the inventive concept are shown. The inventive concept may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the inventive concept to those skilled in the art. Like numbers refer to like elements throughout the description. Any steps or features illustrated by dashed lines should be considered optional.

As disclosed above, there is still a need for an improved BBU-RRU arrangement.

Furthermore, the inventors of the inventive concept have realized that a desired processing split between RRU and BBU should attempt to meet at least the following three requirements:

the performance should be as good as or at least very close to , which represents the best achievable performance, with a traditional master-remote design, e.g., based on CPRI-type FH interfaces.

The second requirement is to keep the low capacity requirement of the FH interface, which should be decoupled from the number of antennas. It is reasonable to reduce the number of streams (streams) on the FH interface to the number of user layers (alternatively, the number of streams on the FH interface can be reduced to the number of user layers times the number of polarization directions).

The third requirement is to keep the computational complexity required in the RRU low, major constraints on complexity are the real-time computation and updating of beamforming weight coefficients, if all MIMO related processing is implemented in the RRU, such computation may be processing intensive, as MIMO related processing typically involves performing a larger matrix inversion generally considers that the inversion of a large matrix requires a rather high computational complexity.

There may be different approaches regarding the functional split between RRU and BBU. Fig. 1 and 2 give two examples of such functional splits.

In particular, fig. 1 and 2 have block diagrams of BBU- RRU arrangements 100a, 100b of two different examples of functional split between BBU and RRU with respect to beamforming or MIMO operation for uplink processing of signals received at antennas (antennas 1, …, antenna 64) of the access node from served wireless devices (UE 1, UE 2). Functional splits are marked by dotted lines. Each BBU- RRU arrangement 100a, 100b comprises: an optional Discrete Fourier Transform (DFT) block 110 that performs a DFT on the uplink signals of the subcarriers across all antenna elements, which transforms the received signals to the directional domain; a Zero Forcing (ZF) interference cancellation or Minimum Mean Square Error (MMSE) interference cancellation block 120 configured to perform interference cancellation on the transformed signal; an equalization block 130 configured to perform equalization on the signal after interference cancellation; and a demodulation block 140 configured to demodulate the equalized signal. The BBU-RRU arrangement 100b further comprises a selection block 150 configured to select only a subset of signals received from different directions or antenna elements.

The block diagram in fig. 1 represents an example of a BBU-RRU arrangement where all interference cancellation of the uplink signal is performed by the RRU disadvantages of this example are that the complexity of calculating the cancellation coefficients is rather high, resulting in high calculation requirements for the RRU.

The block diagram in fig. 2 represents an example of a BBU-RRU arrangement where the number of signal components is reduced by antenna or direction selection in the RRU before samples of the uplink signal are sent to the BBU for interference cancellation.

In aspects, a frequency domain implementation for OFDM systems such as so-called Long Term Evolution (LTE) and New air interface (NR) telecommunication systems is assumed.accordingly, the uplink signals received at each antenna element are first transformed to the frequency domain by a DFT.this DFT block is omitted from FIGS. 1 and 2 for simplicity of mathematical modeling and illustration.basically, in FIGS. 1 and 2, the uplink signals received at each antenna element represent subcarriers.

The operations required to perform massive MIMO processing in RRUs according to the method illustrated in fig. 1 this method is able to meet the and second requirements however, the required computational complexity of RRUs needs to be rather high in view of e.g. the computational complexity of determining the beamforming or MIMO coefficients.

The second approach, shown in fig. 2, reduces the required computational complexity required in the RRU by selecting uplink signals for only a subset of antenna elements or directions and delivering the selected uplink signals to the BBU over the FH interface for further steps of processing (e.g., involving MIMO operation).

To obtain such a mechanism, an RRU200, a method performed by an RRU200, a computer program product comprising code, e.g., in the form of a computer program, which when run on processing circuitry of an RRU200 causes the RRU200 to perform the method are provided, to obtain such a mechanism, a BBU300, a method performed by a BBU300, and a computer program product comprising code, e.g., in the form of a computer program, which when run on processing circuitry of a BBU300 causes the BBU300 to perform the method are provided at step .

Reference is now made to fig. 3, which illustrates a method of processing an uplink signal performed by RRU200 according to an embodiment.

The RRU processes signals received from the wireless device at antenna elements of an antenna array of the RRU. Thus, the RRU is configured to perform step S102:

RRU200 obtains uplink signals received from wireless devices at antenna elements of an antenna array of RRU200 each wireless device is associated with at least user layers of its own.

From the perspective of each user layer, the RRU combines the signals received from the antenna elements or directions in order to capture most of the energy and thereby maximize the signal-to-noise ratio (SNR) for each user layer. In particular, the RRU is configured to perform step S104:

the RRU200 captures energy per user layer the energy per user layer is captured by combining the uplink signals received from the antenna array into a combined signal for each user layer this combination results in combined signals for each individual user layer the combining for each individual user layer is based on the channel coefficients of the wireless devices associated with each individual user layer.

Here, the channel coefficients for the individual user layers correspond to the radio propagation channel from the point in the served wireless device that transmits user layer data to the point in the RRU that receives user layer data in an uplink signal from multiple antenna elements or directions.

, there is therefore a combining operation for each user layer then steps are taken in the BBU to process the thus combined signals accordingly, the RRU is thus configured to perform step S106:

s106: RRU200 provides the combined signal to BBU 300.

In aspects, the combined signal is provided to BBU300 through a FH interface operatively connected between RRU200 and BBU 300.

This functional split between RRU200 and BBU300 meets all three requirements described above.

Embodiments will now be disclosed regarding further steps performed by RRU200 to process uplink signals.

generally, the received uplink signals are combined such that the SNR is improved after combining, where noise in the SNR refers to background noise and/or interference from neighboring cells.

In aspects, the channel coefficients relate to at least channel characteristics of a radio propagation channel extending between the wireless device of each individual user layer and an antenna array of the RRU200 in a direction from the wireless device to the antenna array.

In particular, according to an embodiment, combining coefficients are applied to the uplink signals in order to combine the received uplink signals, wherein the combining coefficients are based on the channel coefficients for each user layer.

No matrix inversion is required for determining the combining coefficients.

The combining coefficients may be determined in the antenna element domain or in the direction domain, that is, according to an embodiment, the combining coefficients are determined per antenna element or per direction in which the uplink signal is received at the antenna element generally refers to a directional beam pointing in that direction.

, the directional domain is a transform of the antenna element domain the directional domain can be interpreted as the domain in which series of directional beams are simultaneously formed to cover a range of directions.

According to an embodiment, the uplink signals of each antenna element are transformed into uplink signals of each direction before applying the combining coefficients to the uplink signals of each direction. For example, a spatial DFT (i.e., a DFT performed on the antenna elements) may be applied to the uplink signals from the antenna elements in order to transform the uplink signals from the antenna element domain to the direction domain.

Determining the combining coefficients based on the direction domain channel estimates may be advantageous because the channel is more colored and the angular spread is smaller in the direction domain than in the antenna element domain, resulting in a higher SNR in the direction of the concentrated uplink signal. Therefore, the channel coefficient can be estimated more accurately.

The combining in step S104 may be performed in the antenna element domain or in the directional domain. That is, according to an embodiment, combining coefficients are applied to each antenna element or uplink signal of each direction in which the uplink signal is received at the antenna element. Since the combining coefficient can be converted by the transform operation, the combining can be performed in the antenna element domain or in the direction domain. The inverse dft (idft) may be applied to the combined coefficients in the directional domain to obtain the combined coefficients in the antenna element domain. That is, according to an embodiment, the combining coefficients determined per direction are transformed into combining coefficients per antenna element.

The combining may be performed for only a subset of the antenna elements or directions.

In aspects, the combining in step S104 is performed only for a subset of the antenna elements therefore, according to an embodiment, RRU200 is configured to perform step S104a (optional) which is part of of step S104:

s104 a: RRU200 selects uplink signals to be received from less than all of the antenna elements for each user layer to be combined into a combined signal.

In aspects, the combining in step S104 is performed only for a subset of directions, thus, according to an embodiment, RRU200 is configured to perform (optional) step S104b, which is part of of step S104:

s104 b: when applying combining coefficients to the uplink signals for each direction, RRU200 chooses for each user layer to combine the received uplink signals from less than all directions into a combined signal.

According to embodiments, for each user layer, uplink signals received from at least as many antenna elements as the total number of user layers are combined into a combined signal.

The subset should be chosen so that most of the energy is captured for each user layer. Thus, the channel coefficients may be used as a basis when determining from which antenna elements or directions to combine the received uplink signals. That is, according to an embodiment, the received uplink signals are determined from which less than all antenna elements or directions to combine based on the channel coefficients.

The benefits of selecting only a subset of antenna elements or directions for combining are that it can reduce the computational complexity required for combining.

The channel coefficients may be estimated using reference signals such as demodulation reference signals (DMRS) and/or Sounding Reference Signals (SRS). That is, according to an embodiment, the uplink signal comprises a reference signal, and wherein the reference signal received from the antenna element or direction is extracted when capturing energy, in order to enable estimation of the channel coefficients using the reference signal.

Each user layer may correspond to independently scheduled information and thus represent a MIMO layer. In particular, according to an embodiment, the received signal in each user layer includes independently scheduled information.

In some aspects separate streams of uplink signals are transmitted for each polarization direction therefore, according to embodiments, the received uplink signals are combined into separate combined signals for each polarization direction of the antenna elements furthermore, in this regard, combined signals may comprise different polarization directions or the combination may be performed separately for each polarization direction, if the combination is performed separately for each polarization, then combined signals exist for each user layer and polarization.

In the case of two polarization directions, RRU200 may be configured to combine the received uplink signals (e.g., MRC or IRC) separately for each polarization direction, providing combined signals to BBU300 per polarization direction and per user layer, or combine the received uplink signals jointly for both polarization directions, including signals of both polarization directions (e.g., MRC or IRC) in the combined signal per user layer, or use MRC for each polarization direction, then use IRC between the signals for each polarization direction, to combine the received uplink signals, resulting in combined signals per user layer.

If using e.g. MRC, it may be advantageous to perform combining separately for each polarization direction and then provide the thus separated combined signal for each polarization direction to the BBU for further steps of processing (e.g. interference cancellation/suppression) — including both polarization directions when performing MRC gives a lower fronthaul bit rate but may give worse performance when considering interference from neighboring cells if the combining includes some kind of IRC, the performance may be as good as or almost when sending the separated combined signal for each polarization direction over the FH interface.

Referring now to fig. 4, a method for processing uplink signals performed by BBU300 is shown, according to an embodiment.

As disclosed above, the RRU provides the combined signal to the BBU in step S106. Therefore, assume that the BBU is configured to perform step S202:

BBU300 obtains combined signals from RRU200 as disclosed above, each combined signal represents a combination of uplink signals received from wireless devices at antenna elements of an antenna array of RRU200, where each wireless device is associated with at least user layers of its own.

In aspects, the combined signal is obtained by BBU300 through a FH interface operatively connected between RRU200 and BBU 300.

Thus, the BBU is configured to cancel interference and separate the user layer signals, e.g., for further decoding steps, therefore, the BBU is configured to perform steps S204 and S206:

s204: the BBU300 performs interference cancellation on each of the combined signals. And the interference elimination obtains the combined signal after the interference elimination.

The BBU300 separates the interference cancelled combined signal into separate uplink signals for each user layer, such that there are separate user layers for each separate uplink signal S206.

Embodiments will now be disclosed regarding further step details of processing uplink signals performed by the BBU 300.

There may be different methods to perform interference cancellation in step S204. According to an embodiment, interference is cancelled using linear cancellation such as zero-forcing (ZF) based interference cancellation or Minimum Mean Square Error (MMSE) based interference cancellation or non-linear cancellation such as Successive Interference Cancellation (SIC).

As disclosed above, the combined signal may represent uplink signals received for only a subset of the antennas. That is, according to an embodiment, the combined signal represents an uplink signal combined from less than all antenna elements.

As disclosed above, the combined signal may represent uplink signals received for only a subset of the directions. That is, according to an embodiment, the combined signal represents an uplink signal combined from less than all directions in which the uplink signal is received at the antenna element.

The computation of the cancellation coefficients typically involves a matrix inversion operation and may therefore require a high computational complexity. However, the required computational complexity is lower than if the interference cancellation is performed directly on the uplink signals obtained from the antenna elements, since the number of signals has been reduced to the number of user layers.

In aspects, the beamforming sub-function for energy capture per user layer is performed in the RRU200 and the second beamforming sub-function for interference cancellation between user layers after the beamforming operation is performed in the BBU300 beamforming is equivalent to spatial domain combining for MIMO systems so it can be explained that steps S102-S104 (and optionally any of S104a, S104 b) define the beamforming sub-function that forms beams for each user layer in order to capture most of the energy and maximize SNR while keeping the channel matrix good after combining in this sense the uplink signals can be considered as transformed to the beam domain when steps S102-S104 (and optionally any of S104a, S104 b) have been performed, furthermore it can be explained that steps S202-S206 define the second beamforming sub-function for cancellation.

The process can be illustrated by the following example using a ZF-based approach. For MIMO systems with a channel matrix H, ZF beamforming coefficients are applied to cancel the interference between user layers. Following the ZF principle, the ZF beamforming coefficient C can be formulated as the pseudo-inverse of the channel matrix H, which can be expressed as:

wherein H⁺Represents the pseudo-inverse of H, an

Hermitian transpose of H. Applying ZF coefficient C to the received signal from the antenna element, the received signal after cancellation can beyExpressed as:

in the above expression, n represents channel noise, and x is a transmitted signal. In addition, let

And is

Then the received signal may be processedyStep is expressed as:

as can be seen, the cancellation matrix C can be decomposed intoIn which willIs interpreted as an MRC operation and will

Interpreted as ZF cancellation for the received signal after MRC. Thus, a complete ZF process can be seen as two sub-processes: MRC and smaller ZF. This matches the functional split between RRU and BBU proposed herein. In this case, the proposed functional split between RRU and BBU thus achieves full cancellation performance. The same principles apply to other types of cancellation schemes, such as MMSE-based cancellation schemes.

Fig. 5 shows a block diagram of the RRU and BBU proposed herein provided in an access node 400 in the illustrative example of fig. 5, the access node includes 64 antenna elements (antenna 1, …, antenna 64) and serves two wireless devices (UE 1 and UE 2) with antenna elements on each wireless device.

The uplink signals from UE1 and UE2 are received at 64 antennas of the access node and thus obtained by the RRU (as in step S102).

In aspects , the uplink signals received at each antenna element represent subcarriers, and thus the methods disclosed with respect to fig. 3, 4 and 5 are used to process the uplink signals in the frequency domain.

If the combining coefficients are to be determined in the direction domain, the uplink signal is transformed to the direction domain by applying a DFT to the uplink signal across 64 antenna elements at DFT block 110. This is not needed if the combining coefficients are to be determined in the antenna element domain.

Similarly, channel estimation may also be performed in the direction domain by applying a DFT to the reference signal and then estimating channel coefficients in the direction domain based on the reference signal received after the DFT. From the channel coefficients estimated in the direction domain, IDFT may be applied to obtain the channel coefficients in the antenna element domain.

Optionally, a subset of the signal contributions from each wireless device is selected at selection blocks 150a, 150b (as in steps S104a or S104 b). specifically, methods of selecting signal contributions for each user layer are where (1) the number of selected signal contributions is greater than or equal to the total number of user layers and (2) the selected signal contributions capture most of the energy for each user layer.

The signals are then coherently combined for each user layer based on the same channel estimates for each user to maximize the SNR (as in step S104). As an example, MRC is used for each user layer at MRC blocks 160a, 160 b.

After the signal combination, the number of received signals is reduced to the number of user layers. These signals are then delivered to the BBU through the FH interface (as in steps S106, S202).

There may still be mutual interference between user layers because no explicit interference cancellation has been performed. Thus, in the BBU, interference is cancelled (as in step S204), for example, using a Zero Forcing (ZF) based method, a Minimum Mean Square Error (MMSE) based method, or the like at ZF/MMSE block 120. Thus, interference cancellation is only performed for as many signals as the user layer, thereby reducing the computational complexity requirements needed to determine the cancellation coefficients compared to the requirements needed for full interference cancellation performed directly in the antenna elements or directions (as is the case with the BBU-RRU arrangement of fig. 1).

After interference cancellation, the user layer signal is separated (as in step S206) for further processing, such as equalization (at equalization block 130), demodulation (at demodulation block 140), decoding, and so on.

Simulation results of the BBU and RRU disclosed herein (as in fig. 5) are now compared to the BBU-RRU arrangements of fig. 1 and 2.

For the BBU-RRU arrangement of FIG. 2, two types of implementations have been used, the implementation is denoted as 'method 2 maximum sum Power', and is based on selecting the signal component with the largest energy for all users given the number of signal components to be selected.

Next, the simulation setup will be described.

The access node uses a 64-element uniform linear antenna array with half-wavelength spacing between adjacent antenna elements, and each antenna element is omnidirectional. All elements have the same polarization.

There are 16 wireless devices being served, each having antennas, so there are 16 user layers in total, with each wireless device having layers.

The radio propagation channel comprises two multipath clusters (clusters), wherein each multipath cluster comprises line-of-sight components (representing the strongest component in each cluster) and five multipath components, the amplitude of each component is rayleigh distributed and the phase is evenly distributed in the interval [ -pi, pi ], the multipath components have a power 5-10dB lower than the line-of-sight components the power offset is evenly distributed in [5,10] dB, the angle of arrival (AoA) of the line-of-sight component is evenly distributed in [ -60,60] degrees, assuming coverage of a 120 degree cell sector, the multipath components have an angular spread of 5 degrees in each cluster, which is evenly distributed in-2.5, 2.5] degrees around the AoA of the line-of-sight component.

The simulation is performed in the direction domain by a 64-point DFT (as implemented using FFT), which means that the dashed boxes illustrated in fig. 1, 2 and 3 are used.

Channel estimation is performed in the direction domain to improve the estimation accuracy, i.e. to increase the estimated SNR for strong directions.

The received SNR per antenna element is set to 0 dB. The SNR for the channel estimation is set to 0, 3 and 6 dB.

ZF interference cancellation is used. For the BBU-RRU arrangement of fig. 1, ZF interference cancellation is applied directly to all 64 signal components. For the BBU-RRU arrangement of fig. 2, 32 signal components are selected. Then, ZF interference cancellation is applied to the selected signal component. For the proposed BBU and RRU, the 16 strongest signal components per wireless device are selected for MRC. After MRC, 16 combined signals are formed. Then, ZF interference cancellation is applied to the 16 combined signals. All selection and cancellation operations are based on the estimated channel with the assumed estimated SNR.

Fig. 6 shows the Cumulative Distribution Function (CDF) of SNR for all served wireless devices after interference cancellation, where the average SNR per antenna is set to 0dB and the same SNR is set for channel estimation.

Fig. 7 shows the CDF of SNR for all served wireless devices after interference cancellation, where the average SNR per antenna is set to 0dB, and an improved SNR of 3dB is set for the channel estimate.

Fig. 8 shows the CDF of SNR for all served wireless devices after interference cancellation, where the average SNR per antenna is set to 0dB, and an improved SNR of 6dB is set for the channel estimate.

Fig. 9 shows the CDF of SNR for all served wireless devices after interference cancellation, where the average SNR per antenna is set to 0dB and the channel estimation is perfect.

Simulation results show that the proposed BBU and RRU have the best performance, even slightly better than the BBU-RRU arrangement of fig. 1 with complete cancellation reasons are that the selective MRC excludes weak signal contributions of low SNR.

Simulation results show that although both implementations of the BBU-RRU arrangement of fig. 2 double the number of signal contributions to 32, this has the overall worst performance reasons for this are that a relatively large number of signal contributions are needed to capture most of the energy.

The results also show that: the performance would be significantly improved if the channel estimation SNR were improved. This also proves to be justified to have interference cancellation functionality in the BBU, such as implemented by the proposed BBU and RRU.

Embodiments disclosed herein may be applied to active distributed antenna systems such as the so-called radio point system (RDS), in typical RDS, each radio point unit may have 2 or 4 antennas several clusters of radio point units are connected to an Indoor Radio Unit (IRU) and time domain uplink signals are grouped together by the IRU into small groups (cells) then the combined signals are sent to a BBU for further processing in steps.

For example, with 4 antennas on each radio point unit and combining 8 radio point units into small groups, in RRU, the received streams from 32 antenna elements are first transformed to the frequency domain and the methods disclosed herein are applied on each subcarrier or group of subcarriers.

Fig. 10 schematically shows the components of the RRU200 according to an embodiment in terms of a number of functional units the processing circuit 210 is provided using any combination of or more of a suitable Central Processing Unit (CPU), multiprocessor, microcontroller, Digital Signal Processor (DSP), etc. capable of executing software instructions stored in, for example, a computer program product 1410a in the form of a storage medium 230 (as in fig. 14), the processing circuit 210 may also be provided as at least Application Specific Integrated Circuits (ASICs) or field programmable arrays (FPGAs).

In particular, the processing circuitry 210 is configured to cause the RRU200 to perform operations or set of steps S102-S106 as disclosed above. For example, the storage medium 230 may store a set of operations, and the processing circuit 210 may be configured to retrieve the set of operations from the storage medium 230, causing the RRU200 to perform the set of operations. The set of operations may be provided as a set of executable instructions. Thus, the processing circuitry 210 is thereby arranged to perform the methods disclosed herein.

The storage medium 230 may also include a persistent storage device, which may be, for example, any single memory or combination of magnetic, optical, solid state, or even remotely mounted memory.

RRU200 can also include a communication interface 220 for communicating over an air interface with at least the wireless device and with BBU300 over a FH interface accordingly, communication interface 220 can include or more transmitters and receivers that include analog and digital components.

Processing circuitry 210 controls -like operation of RRU200, for example, by sending data and control signals to communication interface 220 and storage medium 230, by receiving data and reports from communication interface 220, and by retrieving data and instructions from storage medium 230 other components and related functionality of RRU200 are omitted so as not to obscure the concepts presented herein.

The RRU200 of fig. 11 comprises a plurality of functional modules, an obtaining module 210a configured to perform step S102, an acquisition module 210b configured to perform step S104, and a providing module 210e configured to perform step S106 the RRU200 of fig. 11 may further comprise a plurality of optional functional modules, such as any of a -selecting module 210c configured to perform step S104a and a second-selecting module 210d configured to perform step S104 b. generally, each functional module 210a-210e may be implemented in hardware or in software.

FIG. 12 schematically shows the components of BBU300 according to an embodiment in terms of a number of functional units processing circuit 310 is provided using any combination of or more of a suitable Central Processing Unit (CPU), multiprocessor, microcontroller, Digital Signal Processor (DSP), etc. capable of executing software instructions stored in, for example, a computer program product 1410b in the form of storage medium 330 (as in FIG. 14). processing circuit 310 may also be provided as at least Application Specific Integrated Circuits (ASICs) or field programmable arrays (FPGAs).

In particular, the processing circuit 310 is configured to cause the BBU300 to perform operations or sets of steps S202-S206 as disclosed above. For example, the storage medium 330 may store a set of operations, and the processing circuit 310 may be configured to retrieve the set of operations from the storage medium 330, causing the BBU300 to perform the set of operations. The set of operations may be provided as a set of executable instructions. Thus, the processing circuitry 310 is thus arranged to perform the methods disclosed herein.

The storage medium 330 may also include a persistent storage device, which may be, for example, any single memory or combination of magnetic, optical, solid-state, or even remotely-mounted memory.

BBU300 may also include a communication interface 320 for communicating with at least RRU200 over the FH interface and with other network nodes, entities, devices, and functions over at least other interfaces accordingly, communication interface 320 may include or more transmitters and receivers that include analog and digital components.

The processing circuit 310 controls the -like operation of the BBU300, for example, by sending data and control signals to the communication interface 320 and the storage medium 330, by receiving data and reports from the communication interface 320, and by retrieving data and instructions from the storage medium 330, other components and related functionality of the BBU300 are omitted so as not to obscure the concepts presented herein.

FIG. 13 schematically shows the components of BBU300 according to an embodiment in terms of a plurality of functional modules, BBU300 of FIG. 13 includes a plurality of functional modules, an obtaining module 310a configured to perform step S202, an interference cancellation module 310b configured to perform step S206, and a separating module 310c configured to perform step S206, each of the functional modules 310a-310c may be implemented in hardware or in software, preferably or more or all of the functional modules 310a-310c may be implemented by the processing circuitry 310, possibly in cooperation with the communication interface 320 and/or the storage medium 330, accordingly, the processing circuitry 310 may be arranged to extract instructions provided by the functional modules 310a-310c from the storage medium 330 and arranged to execute these instructions, thereby performing any of the steps of BBU300 disclosed herein.

RRU200 and BBU300 may be provided as stand-alone devices or as portions of at least additional devices, for example, as disclosed above, RRU200 and BBU300 may be provided in an access node-that is, as in fig. 5, access node 400 may include BBU300 as set forth herein and at least RRUs 200 as set forth herein-alternatively, the functionality of RRUs 200 and BBU300 may be distributed between at least two devices or nodes.

Thus, part of the instructions executed by the RRU200 or BBU300 can be executed in the device and a second part of the instructions executed by the RRU200 or BBU300 can be executed in a second device, the embodiments disclosed herein are not limited to any particular number of devices on which the instructions executed by the RRU200 or BBU300 can be executed.

Fig. 14 shows examples of computer program products 1410a, 1410b including computer readable means 1430 on this computer readable means 1430, the computer program 1420a can cause the processing circuitry 210 and the entities and devices operatively coupled thereto, such as the communication interface 220 and the storage medium 230, to perform methods according to embodiments described herein can be stored, accordingly, the computer program 1420a and/or the computer program product 1410a can provide means for performing any steps of the RRU200 disclosed herein, on this computer readable means 1430, the computer program 1420b can cause the processing circuitry 310 and the entities and devices operatively coupled thereto, such as the communication interface 320 and the storage medium 330, to perform methods according to embodiments described herein can be stored, accordingly, the computer program 1420b and/or the computer program product 1410b can provide means for performing any steps of the BBU300 disclosed herein.

In the example of fig. 14, the computer program products 1410a, 1410b are illustrated as optical discs, such as CDs (compact discs) or DVDs (digital versatile discs) or blu-ray discs. The computer program product 1410a, 1410b may also be embodied as a memory, such as a Random Access Memory (RAM), a Read Only Memory (ROM), an Erasable Programmable Read Only Memory (EPROM) or an Electrically Erasable Programmable Read Only Memory (EEPROM), and more particularly as a non-volatile storage medium of the device in an external memory such as a USB (universal serial bus) memory or a flash memory such as a compact flash memory. Thus, although the computer programs 1420a, 1420b are here schematically shown as tracks on the depicted optical disc, the computer programs 1420a, 1420b may be stored in any way suitable for the computer program products 1410a, 1410 b.

The inventive concept has mainly been described above with reference to a few embodiments. However, as is readily apparent to a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the inventive concept, as defined by the appended patent claims.