CN112425079A

CN112425079A - Processing of reference signals in precoding

Info

Publication number: CN112425079A
Application number: CN201880095722.6A
Authority: CN
Inventors: 邵叙宁; F·福克; E·维索特斯基
Original assignee: Nokia Shanghai Bell Co Ltd; Nokia Networks Oy
Current assignee: Nokia Shanghai Bell Co Ltd; Nokia Oyj
Priority date: 2018-07-16
Filing date: 2018-07-16
Publication date: 2021-02-26
Anticipated expiration: 2038-07-16
Also published as: WO2020014825A1; CN112425079B

Abstract

Embodiments of the present disclosure relate to an apparatus, method, and computer-readable storage medium for processing reference signals in precoding. In an example embodiment, a first set of transmission layers is selected from a plurality of transmission layers via a plurality of antennas at a transmitter. Both feedback processing and feedforward processing are performed on a first set of reference signals to be transmitted on a first set of transmission layers. The first set of reference signals is transmitted on a first set of transmission layers. Further, a second set of transport layers is selected from the plurality of transport layers. For the second set of transmission layers, feed forward processing is applied to the reference signal only. In this way, interference measurement and cancellation can be achieved at the receiver side on the selected layer, and thus receiver gain and system performance can be improved.

Description

Processing of reference signals in precoding

Technical Field

Embodiments of the present disclosure relate generally to the field of signal processing, and in particular, to an apparatus, method, and computer-readable storage medium for processing reference signals in precoding.

Background

Non-linear precoding (NLP) techniques are proposed to improve multi-user multiple-input multiple-output (MU-MIMO) performance in New Radios (NR). NLP techniques can potentially achieve significantly higher throughput compared to linear precoding techniques, especially if the users' channels are highly correlated in the spatial domain.

The Tomlinson-Harashima precoding (THP) technique is a sub-optimal variant of NLP, which is attractive due to its low complexity. In THP, interference between different simultaneous transmission layers can be avoided by feedback processing. For example, on the downstream layers, the signal to be transmitted is predistorted by a feedback process to cancel interference from the signal to be transmitted on one or more upstream layers. In the context of the present disclosure, an upstream layer refers to one of a plurality of transport layers on which signals are first processed for transmission, and a downstream layer refers to one of a plurality of transport layers on which signals are subsequently processed for transmission. Signals on the upstream and downstream layers are transmitted simultaneously via multiple antennas.

To enable non-linear or linear precoding, network devices such as NR nodeB (or gNB) require knowledge of the channel state so that the network devices can design precoding matrices to compensate for the effect of the channel on the signal transmission. For example, the channel state may be obtained from Channel State Information (CSI) feedback of a terminal device, such as a User Equipment (UE). As another example, the UE may transmit a Sounding Reference Signal (SRS) to the network device. Through channel reciprocity, a network device may obtain a channel state based on an SRS. The UE also needs CSI for the reception process. The UE may measure CSI from demodulation reference signals (DMRS) known to both the gNB (as a transmitter) and the UE (as a receiver). In NLP, since feedback processing is used for mitigating interlayer interference, it is necessary to specially process a reference signal.

Disclosure of Invention

In general, example embodiments of the present disclosure provide devices, methods, and computer-readable storage media for processing reference signals in precoding.

In a first aspect, an apparatus is provided. The apparatus includes at least one processor and at least one memory including computer program code. The at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus to: selecting, at a transmitter, a first set of transmission layers from a plurality of transmission layers via a plurality of antennas; performing both feedback processing and feedforward processing on a first set of reference signals to be transmitted on a first set of transmission layers; and transmitting the first set of reference signals on the first set of transmission layers. Further, the apparatus is caused to select, at the transmitter, a second set of transmission layers other than the first set of transmission layers from the plurality of transmission layers via the plurality of antennas. Performing feed-forward processing on a second set of reference signals to be transmitted on a second set of transmission layers from the plurality of transmission layers while avoiding feedback processing on the second set of reference signals; and transmitting a second set of reference signals on a second set of transmission layers concurrently with the first set of reference signals.

In a second aspect, a method at a transmitter is provided. In the method, a first set of transmission layers is selected from a plurality of transmission layers via a plurality of antennas. Both feedback processing and feedforward processing are performed on a first set of reference signals to be transmitted on a first set of transmission layers. Then, a second set of transport layers other than the first set of transport layers is selected from the plurality of transport layers. Feed-forward processing is performed on a second set of reference signals to be transmitted on a second set of transmission layers while avoiding feedback processing of the second set of reference signals. A first set of reference signals is transmitted on a first set of transmission layers and a second set of reference signals is simultaneously transmitted on a second set of transmission layers.

In a third aspect, an apparatus is provided that includes at least one processor and at least one memory including computer program code. The at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus to: receiving an indication of a first reference signal type for a first set of transmission layers to indicate that both feedback processing and feedforward processing have been performed on the first set of reference signals on the first set of transmission layers; receiving an indication of a second reference signal type for a second set of transmission layers to indicate that feedforward processing has been performed on the second set of reference signals on the second set of transmission layers without performing feedback processing on the second set of reference signals; simultaneously receiving a first set of transport layers and a second set of transport layers; and decoding the first set of transport layers and the second set of transport layers based on the first indication and the second indication.

In a fourth aspect, there is provided a method comprising: receiving an indication of a first reference signal type for a first set of transmission layers to indicate that both feedback processing and feedforward processing have been performed on the first set of reference signals on the first set of transmission layers; receiving an indication of a second reference signal type for a second set of transmission layers to indicate that feedforward processing has been performed on the second set of reference signals on the second set of transmission layers without performing feedback processing on the second set of reference signals; simultaneously receiving a first set of transport layers and a second set of transport layers; and decoding the first set of transport layers and the second set of transport layers based on the first indication and the second indication.

In a fifth aspect, a computer readable storage medium having a computer program stored thereon is provided. The computer program, when executed by a processor, causes the processor to perform the method according to the second or fourth aspect.

It should be understood that this summary is not intended to identify key or essential features of the embodiments of the disclosure, nor is it intended to be used to limit the scope of the disclosure. Other features of the present disclosure will become readily apparent from the following description.

Drawings

Some example embodiments will now be described with reference to the accompanying drawings, in which:

fig. 1 illustrates an example architecture of a THP-enabled communication system;

FIG. 2 illustrates an example environment in which embodiments of the present disclosure may be implemented;

FIG. 3 illustrates a flow diagram of an example method according to some embodiments of the present disclosure;

fig. 4 illustrates an example partitioning process of multiple transport layers in accordance with some other embodiments of the present disclosure;

fig. 5 shows a flow diagram of an example method according to some other embodiments of the present disclosure;

fig. 6 illustrates an example signaling diagram between a transmitter and a receiver in accordance with some embodiments of the present disclosure;

fig. 7 illustrates an example comparison of different schemes for processing reference signals in a 8 UE per cell scenario, in accordance with some embodiments of the present disclosure;

fig. 8 illustrates an example comparison of different schemes for processing reference signals in a 12 UE per cell scenario, in accordance with some embodiments of the present disclosure;

fig. 9 illustrates an example power ratio between a full DMRS and data, in accordance with some embodiments of the present disclosure; and

FIG. 10 shows a simplified block diagram of a device suitable for implementing embodiments of the present disclosure.

Throughout the drawings, the same or similar reference numbers refer to the same or similar elements.

Detailed Description

The principles of the present disclosure will now be described with reference to a few exemplary embodiments. It is understood that these embodiments are described for illustrative purposes only and are presented to aid those skilled in the art in understanding and enabling the disclosure, without placing any limitation on the scope of the disclosure. In addition to the manner described below, the disclosure described herein may be implemented in a variety of other ways.

In the following description and claims, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs.

As used herein, the term "transmitter" refers to a device capable of transmitting a signal. As used herein, the term "receiver" refers to a device capable of receiving a signal. The transmitter or receiver may be implemented by or as part of any suitable device, including, for example, a network device or a terminal device.

As used herein, the term "network device" refers to any suitable device at the network side of a communication network. The network device may comprise any suitable device in an access network of a communication network, including, for example, a Base Station (BS), a relay, an Access Point (AP), a node B (NodeB or NB), an evolved NodeB (eNodeB or eNB), a gigabit NodeB (gnb), a remote radio module (RRU), a Radio Header (RH), a Remote Radio Head (RRH), a low power node (such as femto, pico, etc.).

As used herein, the term "terminal device" refers to a device that is capable, configured, arranged and/or operable to communicate with a network device or another terminal device in a communication network. The communication may involve the transmission and/or reception of wireless signals using electromagnetic signals, radio waves, infrared signals, and/or other types of signals suitable for the transmission of information over the air. In some embodiments, the terminal device may be configured to transmit and/or receive information without direct human interaction. For example, when triggered by an internal event or an external event, or in response to a request from the network side, the terminal device may transmit information to the network device on a predetermined schedule.

Examples of end devices include, but are not limited to, User Equipment (UE), such as a smart phone, a wireless enabled tablet, a laptop embedded device (LEE), a laptop installed device (LME), and/or a wireless Customer Premises Equipment (CPE). For purposes of discussion, some embodiments will be described with reference to a UE as an example of a terminal device, and the terms "terminal device" and "user equipment" (UE) may be used interchangeably in the context of this disclosure.

As used herein, the term "circuit device" may refer to one or more or all of the following:

(a) a purely hardware circuit implementation (such as an implementation in analog and/or digital circuit means only), and

(b) a combination of hardware circuitry and software, such as (as applicable): (i) a combination of analog and/or digital hardware circuitry and software/firmware, and (ii) a hardware processor with software (including a digital signal processor), any portion of software and memory that work together to cause a device such as a mobile phone or server to perform various functions, and (ii) a computer program product

(c) Hardware circuitry and/or a processor, such as a microprocessor or a portion of a microprocessor, that requires software (e.g., firmware) to operate but may not be present when operation is not required.

This definition of "circuit arrangement" applies to all uses of this term in this application, including in any claims. As another example, as used in this application, the term "circuitry" also encompasses only a portion of an implementation of a hardware circuit or processor (or multiple processors) or a hardware circuit or processor and its (or their) accompanying software and/or firmware. The term "circuitry" also encompasses (e.g., and where applicable to the particular claim element (s)) a baseband integrated circuit or processor integrated circuit for a mobile device, or a similar integrated circuit in a server, a cellular network device, or other computing or network device.

As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. The term "comprising" and its variants are to be understood as open-ended terms meaning "including but not limited to". The term "based on" should be understood as "based at least in part on". The terms "one embodiment" and "an embodiment" should be understood as "at least one embodiment". The term "another embodiment" should be understood as "at least one other embodiment". Other definitions (explicit and implicit) may be included below.

For THP in NR, two types of processing of DMRS have been proposed, which will be described below with reference to fig. 1. Fig. 1 shows an example architecture of a THP-enabled communication system 100. In system 100, feedforward filter (F)105 is designed to derive the lower triangular estimated effective channel

Wherein K representsThe number of transport layers (or streams),

which indicates that the desired receive filter is to be received,

indicating an estimated physical channel based on the order of layers (or streams). Lower triangular effective channel

It can be ensured that there is no interference from the downstream layer to the upstream layer.

For each Resource Element (RE), the original symbol

Processed by a feedback filter (B-I)110 to avoid interference from upstream layers to downstream layers, and processed by a modulo (modulo) device 115 to limit transmit power. The B matrix is a scaled version of the effective channel. Suppose that

Wherein the diagonal element b_i，iThe channels of the ith layer after scaling are represented and normalized to 1. The pre-distorted symbol of the i-th layer after the feedback process and the modulus process is denoted as s_i＝x_i-∑_j＜ib_i，js_j+p_iWherein each upstream layer j corresponds to a predistortion offset-b_i，js_j。p_iRepresents the modulo offset of the i-th layer, and p if the pre-distorted symbol is within the constellation boundary before modulo _i0. The feedback process and the modulo process may be expressed as X + P- (B-I) S ═ S, or equivalently, as S ═ B^-1(X + P) wherein

If not, B^-1Representing an equivalent linear filter for the feedback process.

Ideally, if the base station has perfect knowledge of H, the UE will apply the desired receive filter (120) and scaling (125). The effective channel after scaling will be fully represented by the B matrix and the predistortion offset-B_i，js_jInterference from the j-th layer can be perfectly eliminated. In addition, RX modulo device 130 will reverse the modulo offset. In this case, each layer does not interfere.

In practice, the receive filters and scaling weights at the UE side are calculated by channel and interference estimation (135) based on DMRS. The estimated interference power may also be used in demodulation (140). As shown, in THP, the DMRS may be inserted just before the feedforward filter 105 and precoded only by the feedforward filter 405, which is referred to as "feedforward DMRS". Alternatively, the DMRS may be precoded by both the feedback filter 110 and the feedforward filter 105, which is referred to as a "complete DMRS".

In real-world networks, Channel State Information (CSI) at the base station is generally undesirable. Imperfections in CSI may be caused by delays between CSI measurements and data transmission, limited resolution of CSI reports, CSI quantization errors, and the like. Residual interference is inevitable in the case of non-ideal CSI, including when there is a valid channel H^effInterference from downstream layers to upstream layers when not the lower triangle, and interference from upstream layers to downstream layers when predistortion cannot completely cancel interference.

For linear precoding, the UE may estimate the residual interference based on the DMRS. For example, DMRS is typically precoded in the same way as data in linear precoding. The channel and interference estimation of DMRS is relatively accurate. Thus, the receiver filter may be utilized to mitigate interference. The estimated interference power may also be used to calculate log-likelihood ratios (LLRs) during demodulation.

However, for NLP, interference measurement on the receiver side becomes very difficult due to the introduction of the modulo device 115 for power limitation. In NLP, an additional modulo offset of the modulo device is applied to the data, but not to the DMRS. The predistortion of DMRS is different from the predistortion of data, so the additional modulo offset is unknown to the receiver side.

For example, for a full DMRS, no modulo is applied to the DMRS. In the case of ideal CSI, the interference estimation may be accurate because there is no interference after the receive filtering. The interference estimate is also relatively accurate if the modulo offset of the modulo device 115 is not large, that is, most of the pre-distorted symbols are within the constellation boundaries before the modulo. However, when CSI is not ideal and modulo offset is significant, there is a gap between DMRS and data. For data transmission, the RX modulo device 120 can only reverse the TX modulo offset of the target layer and not the modulo offset of the interference layer. The modulo offset partially cancels the predistortion offset for the data transmission and changes the residual interference. Similar to interference estimation, channel estimation from DMRS is also subject to predistortion and modulo offset and is inaccurate in the case of non-ideal CSI.

Another key issue with a full DMRS is that the TX power of the DMRS becomes higher than the data because there is no modulo device to limit the power increase of the pre-distorted DMRS. Since the power of data is reduced through the modulo processing, the power of DMRS also needs to be backed off. The desired power backoff may be dynamic because the channel estimation may deteriorate when the power backoff is excessive. In order to estimate the channel, the UE must know a dynamic power backoff value that may be difficult to inform to the UE.

For feedforward DMRS, only feedforward processing, not feedback processing, is applied to the DMRS. Even though the interference for data transmission may be cancelled by predistortion, DMRS may suffer all upstream-to-downstream interference. In this case, the measured interference from the DMRS is incorrect even in the case of ideal CSI. Furthermore, only a Maximum Ratio Combining (MRC) receiver may be used, and only noise may be used as input for LLR calculation. As a result, feed-forward DMRS cannot benefit from interference measurements at the receiver side.

Some studies were performed on the performance of the full DMRS and the feed-forward DMRS. The potential advantages of a full DMRS with interference measurements may not be achieved with each UE having a single receive antenna and ideal CSI at the base station. The main drawback of the full DMRS comes from the power increase of the pre-distorted DMRS. The full DMRS may have poor performance if the same power reduction is applied to the data and the DMRS, which means that the feed-forward DMRS is better than the full DMRS.

Some approaches focus on reducing the power gap between the full DMRS and the data to improve the performance of the full DMRS. One approach is to apply a phase rotation to the feed-forward precoding vector of each layer and to optimize the phase rotation to minimize the TX power of the DMRS. The optimal phase rotation depends on the original symbols of the DMRS. This approach is particularly effective in case that a Physical Resource Block (PRB) that should use the same feed-forward matrix has only one Resource Element (RE) of the DMRS. However, in NR, each PRB defines multiple DMRS REs (typically one OFDM symbol) to improve channel estimation quality and provide orthogonal DMRS ports. In this case, it is difficult to find a set of phase rotations that can effectively reduce the power of all DMRS REs.

The inventors have found that none of the methods addresses the interference measurement problem in the case of non-ideal CSI, especially the impact from the modulo processing. Furthermore, for a complete DMRS, there is no efficient and efficient method to signal the power offset between the DMRS and the data to the receiver

Embodiments of the present disclosure provide a scheme for adaptively processing a reference signal. According to this scheme, both feedback processing and feedforward processing are applied to a reference signal to be transmitted on a set of transmission layers selected from a plurality of transmission layers via a plurality of antennas. On the remaining transport layers, the reference signal may be subjected to only feedforward processing without feedback processing.

This scheme ensures that both feedback processing and feedforward processing are performed on the selected set of transport layers. Furthermore, interference measurement and cancellation may be achieved at the receiver side, and thus receiver gain and system performance (e.g., throughput) may be improved.

FIG. 2 illustrates an example environment 200 in which embodiments of the present disclosure may be implemented. Environment 200, which is part of a communication network, includes a transmitter 210 and two receivers 220-1 and 220-2 (collectively receivers 220). It should be understood that one transmitter and two receivers are shown for illustrative purposes only, and do not imply any limitation on the scope of the present disclosure. Environment 200 may include any suitable number of transmitters and receivers suitable for implementing embodiments of the present disclosure.

Transmitter 210 and receiver 220 may be implemented by or as part of any suitable device. In some embodiments, the transmitter 210 may be implemented at a network device and the receiver 220 may be implemented at a terminal device. In embodiments where environment 200 is part of a relay communication network. In this example, the transmitter 210 may be implemented at a network device and the receiver 220 may be at a repeater, and vice versa. In some other embodiments, both transmitter 210 and receiver 220 may be implemented at the terminal device in a device-to-device (D2D) communication (which may alternatively be referred to as a sidelink) or a vehicle-to-everything (V2X).

In various embodiments, the transmitter 210 is equipped with multiple transmit antennas. The transmitter 210 may communicate with the receiver 220, which may have one or more antennas, via multiple antennas. The communication may follow any suitable communication standard or protocol, such as Universal Mobile Telecommunications System (UMTS), Long Term Evolution (LTE), LTE-advanced (LTE-a), fifth generation (5G) NR, wireless fidelity (Wi-Fi), and Worldwide Interoperability for Microwave Access (WiMAX) standards, and employ any suitable communication technology including, for example, multiple-input multiple-output (MIMO), Orthogonal Frequency Division Multiplexing (OFDM), Time Division Multiplexing (TDM), Frequency Division Multiplexing (FDM), Code Division Multiplexing (CDM), Bluetooth, ZigBee, and Machine Type Communication (MTC), enhanced mobile broadband (eMBB), massive Machine Type Communication (MTC), and ultra-reliable low delay communication (urrllc) technologies.

Between the transmitter 210 and the receiver 220, a plurality of transport layers are enabled on which reference signals are transmitted from the transmitter 210 to the receiver 220. The reference signal may be any suitable signal or training sequence known at both the transmitter 210 and the receiver 220. For example, the reference signals may include DMRS, Sounding Reference Signals (SRS), and the like.

In various embodiments of the present disclosure, the reference signal is feedback processed and feedforward processed on a set of transport layers selected from a plurality of transport layers. As such, these reference signals may be used for interference cancellation at the receiver 220 to improve receiver performance.

Fig. 3 illustrates a flow diagram of an example method 300 in accordance with some embodiments of the present disclosure. The method 300 may be implemented at the transmitter 210 as shown in fig. 2. For purposes of discussion, the method 300 will be described with reference to fig. 2.

At block 305, a set of transport layers (referred to as a first set of transport layers) is selected from a plurality of transport layers via a plurality of antennas for both feedback processing and feedforward processing. The selection may take into account any suitable factors such as channel correlation, line-of-sight or non-line-of-sight channels, channel change speed, and other channel conditions. For example, if the channels associated with certain transmission layers have relatively high correlation in the spatial domain, these transmission layers may not be selected to avoid too high a power increase of the pre-distorted reference signals from the feedback and feedforward processing. As another example, the transmission layer corresponding to the line-of-sight channel or the slow-changing channel may not be selected since interference may be easily detected and then canceled at the receiver 220.

In some embodiments, a set of reference signals to be transmitted on a selected transmission layer (referred to as a "first set of reference signals") may have a power reduction to back off power increases in data due to feedback and feedforward processing on the first set of transmission layers. In these embodiments, the first set of transmission layers may be selected such that the power increase of the first set of reference signals to be transmitted over the first set of transmission layers is equal to or less than the power decrease of the first set of reference signals to meet the overall power constraint. In this way, the first set of reference signals may be transmitted with limited power and may, for example, not affect the data. In this manner, system performance may benefit from interference measurements at the receiver 220 with reference signals pre-distorted based on feedback processing and feedforward processing.

Upon selecting the first set of transmission layers, at block 310, both feedback processing and feedforward processing are performed on a first set of reference signals to be transmitted over the first set of transmission layers. As described above, the power of the first set of reference signals may be reduced to reduce the increase in data power due to pre-distortion from the feedback and feedforward processes. In some embodiments, each power of the first set of reference signals may be reduced by a predetermined power level. The predetermined power level may be associated with a number of layers, channel conditions, network deployment or scheduling, and the like.

As an example, a semi-static power backoff value may be defined at the transmitter 210 for a first set of reference signals and then indicated to the receiver 220. The indication of the power backoff value may be transmitted in any suitable signaling or message, such as in Dedicated Control Information (DCI), Radio Resource Control (RRC) signaling, Medium Access Control (MAC) Control Element (CE), or the like. The use of a semi-static power back-off value may effectively and efficiently reduce signaling overhead compared to a dynamic power back-off value.

At block 315, another set of transport layers (referred to as a "second set of transport layers") is selected from the plurality of transport layers for feed forward processing only and without performing feedback processing. Similar to the selection of the first set of transmission layers, the selection of the second set of transmission layers may take into account any suitable factors, such as channel correlation, line-of-sight or non-line-of-sight channels, channel change speed, and other channel conditions. In some embodiments, the second set of transmissions may be the remaining layers of the plurality of transmission layers.

At block 320, feed-forward processing is performed on a set of reference signals to be transmitted on a second set of transmission layers (referred to as a "second set of reference signals") while avoiding feedback processing.

An example process of dividing a plurality of transport layers into a first group of transport layers and a second group of transport layers will be described below with reference to fig. 4. In this example, the reference signal is implemented by the DMRS, and all of the transmission layers are selected from the beginning to be included in the first group. As shown in fig. 4, process 400 begins at block 405. Then, the following operations (1) through (7) are performed at block 410.

(1) A power back-off value α dB is defined.

(2) Scheduling K layers.

(3) For each subband (e.g., each subcarrier), feedforward filter F and feedback filter B are computed to obtain data.

(4) Set up K₁＝K。

(5) For each sub-band, set F_DMRS＝F*10^-α/20。

(6) For each sub-band, set B_DMRS＝B。

(7) Will I_KDefined as K x K identity matrix.

For DMRS, the feed forward precoding vector for layer i is F_DMRSColumn i. As shown in operation (5), applying a power backoff (e.g., α dB) to the layer for the full DMRS is equivalent to scaling its feed-forward precoding vector

B_DMRSRow i of (a) contains feedback weights for layer i. The feedback weight for the feed-forward DMRS is set to 0.

At block 415, the power limit is checked by comparing the DMRS power to the data power. For example, for each sub-band, the power limit is limited by | | F | | N²Deciding, wherein | | F | | | is the Frobenius norm of the feedforward matrix of the subband. Since the feedback process without the modulo process is equivalent to

Linear filter of (1), whereby DMRS power is controlled by

And (6) determining. Full and feed-forward DMRS pass-filter

An application is made to precode. In this case, by determining whether Sum (| | F) is shown_DMRSB^-1 _DMRS||²)＜＝Sum(||F||²) The DMRS power and the data power are compared.

If the DMRS power is higher than the data power, process 400 proceeds to block 420, where the lowest downstream layer is switched from the full DMRS layer to the feed-forward DMRS layer. For example, for the handover as shown, the following operations (8) to (10) may be performed.

(8) For each sub-band, set F_DMRS(：K₁)＝F(：，K₁) To the K th of F₁Column assignment to F_DMRSK of₁And (4) columns.

(9) For each sub-band, set B_DMRS(K₁，：)＝I_k(K₁,: ) To the K th of B₁Line assignment to B_DMRSK of₁And (6) rows.

(10) Set up K₁＝K₁-1 to switch the lowest downstream layer from the full DMRS layer to the feed-forward DMRS layer.

The process 400 then returns to block 415 to initiate the next iteration to check the power limit. If it is determined at block 415 that the DMRS power is not higher than the data power, the power limit is satisfied. Process 400 then proceeds to block 425 where K is selected₁An upstream layer. For example, the following operations (11) to (13) may be performed as shown.

(11) For each sub-band, use

And precoding the DMRS.

(12) Mixing

layers

1, 2, K₁Is set as a complete DMRS.

(13) Layer K_I+1，K_I+ 2.. the DMRS type of K is set as a feed-forward DMRS.

The process 400 ends at block 430. In this way, the top K is selected₁The upstream layers act as complete DMRS layers while ensuring that K is kept under power constraints₁And (4) maximizing. In this way, the upstream layers, which are typically slightly affected by the modulo processing, may be selected for the full DMRS to obtain accurate channel and interference estimates at the receiver. Downstream layers that are heavily affected by the modulo processing and require more predistortion offset can be selected for the feed-forward DMRS.

In some embodiments, an indication of a reference signal type for a particular transmission layer may be transmitted to a corresponding receiver. For example, an indication of a reference signal type (referred to as a "first reference signal type") on a first set of transmission layers may be transmitted to indicate that both feedback processing and feedforward processing have been performed on the first set of reference signals. Further, an indication of a second reference signal type (referred to as a "second reference signal type") on the second set of transmission layers may be transmitted to indicate that feed-forward processing has been performed on the second set of reference signals without performing feedback processing.

In embodiments where a predetermined power level for reducing the power of the first set of reference signals is indicated to the receiver, the predetermined reduced power level and the indication of the reference signal type may be jointly encoded and then indicated in one bit to further reduce overhead. For example, for one layer, it is indicated whether a full DMRS is enabled with a power backoff value or a feed-forward DMRS is enabled without a power backoff.

Still referring to fig. 3, in both the feedback and feedforward processing, at block 325 a first set of reference signals are transmitted on a first set of transmission layers and a second set of reference signals are simultaneously transmitted on a second set of transmission layers. Thus, at the receiver side, using the pre-distorted reference signals from the feedback and feedforward processing, interference measurements may be performed for the corresponding transmission layer.

Fig. 5 illustrates a flow diagram of an example method 500 in accordance with some other embodiments of the present disclosure. Method 500 may be implemented at receiver 220 as shown in fig. 2.

At block 505, an indication of a first reference signal type for a first set of transmission layers is received to indicate that both feedback processing and feedforward processing have been performed on the first set of reference signals on the first set of transmission layers. At block 510, an indication of a second reference signal type for a second set of transmission layers is received to indicate that feed-forward processing has been performed on the second set of reference signals on the second set of transmission layers without performing feedback processing on the second set of reference signals.

At block 515, a first set of transport layers and a second set of transport layers are received simultaneously. At block 520, the first and second sets of transport layers are decoded according to the first and second indications.

Decoding may be implemented in any suitable manner. In some embodiments, channel estimation and interference estimation may be performed for a first set of layers based on a first set of reference signals. Channel estimation may be performed for a second set of layers based on a second set of reference signals while avoiding interference estimation. The first set of layers is then decoded using a minimum mean square error receiver. The second set of layers is decoded using a maximum ratio combining receiver. In some embodiments, the predefined power backoff for the first set of transmission layers may be reversed while avoiding reversing the predefined power backoff for the second set of transmission layers.

It should also be understood that all operations and features related to the method 300 described above with reference to fig. 2-4 apply equally to the method 500 and have similar effects. Details will be omitted for the sake of simplicity.

Fig. 6 illustrates an example signaling diagram between a transmitter and a receiver in accordance with some embodiments of the present disclosure. In this example, the transmitter 210 is implemented at the gbb and the receiver 220 is implemented at the UE. The reference signal is implemented by DMRS.

As shown in fig. 6, at block 605, the gNB first defines a power backoff value α dB for the full DMRS and sends this value to the UE via downlink signaling such as RRC configuration, MAC CE, or DCI.

During scheduling, at block 610, the gNB may design and apply feedforward and feedback filters and modulo to the data. Further, the gNB selects a full DMRS or a feed-forward DMRS for each layer. The gNB applies feed-forward and feedback filters and power backoff to the full DMRS. The gNB applies a feed-forward filter to the feed-forward DMRS.

At block 615, a DMRS type is signaled to a UE in a control channel via a DMRS type indicator. At block 620, the gNB transmits the DMRS and data to the UE.

At block 625, for the layer with the full DMRS, the UE performs channel and interference measurements based on the full DMRS and inverts the power backoff for the desired channel. The UE then performs Minimum Mean Square Error (MMSE) receiver processing and LLR calculations based on the residual interference plus noise. The receiver processing is similar to that in linear precoding. For layers with feed-forward DMRS, the UE only needs to apply Maximum Ratio Combining (MRC) receiver processing and noise-based LLR calculation, without any information about interference.

Four transmission schemes were compared in the simulation, including 1) a baseline scheme using linear zero forcing for MMSE receivers, 2) THP using feed-forward DMRS and MRC receivers, 3) THP using full DMRS and MMSE receivers, and 4) THP using adaptive DMRS and DMRS type dependent receivers. For a full DMRS, it is assumed that there is no power limitation for the DMRS. The simulation setup is shown in table I.

TABLE I

Simulation graphs

700 and 800 for 8 UEs per cell and 12 UEs per cell are shown in fig. 7 and 8, respectively. Both LoS and NLoS channels will be considered simultaneously in each scenario. As can be seen from the simulation results, THP is generally better than linear precoding, even though the accuracy of channel estimation and interference measurement is poor in THP. The ratio between the feed-forward DMRS and the full DMRS is highly dependent on the scenario. Feed-forward DMRS performs better in LoS channels, while full DMRS performs better in NLoS channels. This is mainly because NLoS channels are more dynamic and interference suppression becomes more important in NLoS channels. The feed-forward DMRS performs better in a high load (12 UEs) scenario, while the full DMRS performs better in a relatively low load (8 UEs) scenario. The reason is that in high load scenarios, the effect of the modulo process is significant for the last few layers. It is clear that the full DMRS is much better than the feed-forward DMRS for NLoS in fig. 7, and the feed-forward DMRS is much better than the full DMRS for LoS in fig. 8.

The proposed adaptive DMRS always achieves the best performance in all THP schemes, since adaptive DMRS achieves a desired trade-off between gain due to interference measurements and loss due to lack of modulo in DMRS. In this example, the power backoff of the full DMRS is set to 3 dB. A higher backoff value may provide some margin for supporting additional full DMRS layers and make the performance of adaptive DMRS closer to full DMRS. In contrast, adaptive DMRSs with low power backoff values are closer to feed forward DMRSs. DMRS type selection algorithms and power backoff values may be further optimized for different scenarios. For example, in a mixed LoS/NloS scenario, the scheduler may allocate a full DMRS to NloS UEs and a feed-forward DMRS to LoS UEs.

Fig. 9 shows a graph 900 of the power ratio between the complete DMRS and the data when a feed-forward filter and a feedback filter from the data are directly applied to the DMRS. It can be seen that the full DMRS requires much more power than the LoS channel and data in high load scenarios. In other words, in this scenario, the modulo processing of the data is more affected, which means that the accuracy of the channel estimation and interference measurement from the complete DMRS is lower. It is assumed that there is no power limitation imposed for the full DMRS in the simulation, but in practice a power backoff must be applied according to the power ratio. It is difficult to signal a dynamic power ratio if a full DMRS is applied to all layers. In contrast, for adaptive DMRS, only a very limited backoff value of 3dB is required and the overhead in the control channel is as small as one bit per layer. As such, adaptive DMRS improves throughput by selecting a DMRS type for each layer. Joint signaling of DMRS types and power backoff information may further reduce overhead.

In some embodiments, an apparatus capable of performing the method 300 or the method 500 may include means for performing the steps of the method 300 or the method 500. The component may be implemented in any suitable form. For example, the module may be implemented in a circuit device or a software module.

In some embodiments, an apparatus capable of performing method 300 comprises: means for selecting, at a transmitter, a first set of transmission layers from a plurality of transmission layers via a plurality of antennas; means for performing both feedback processing and feedforward processing on a first set of reference signals to be transmitted on a first set of transmission layers; means for selecting, at a transmitter, a second set of transmission layers from the plurality of transmission layers other than the first set of transmission layers via a plurality of antennas; means for performing feed-forward processing on a second set of reference signals to be transmitted on a second set of transmission layers from the plurality of transmission layers while avoiding feedback processing on the second set of reference signals; and means for transmitting a first set of reference signals on the first set of transmission layers and simultaneously transmitting a second set of reference signals on the second set of transmission layers.

In some embodiments, the apparatus may further include means for transmitting an indication of the first reference signal type on the first set of transmission layers to indicate that both feedback processing and feedforward processing have been performed on the first set of reference signals.

In some embodiments, the apparatus may include means for transmitting an indication of a second reference signal type on a second set of transmission layers to indicate that feed-forward processing has been performed on the second set of reference signals without performing feedback processing on the second set of reference signals.

In some embodiments, each of the power of the first set of reference signals and the power of the second set of reference signals is reduced by a predetermined power level.

In some embodiments, the apparatus may further include means for transmitting an indication of a predetermined power level on the first set of transmission layers.

In some embodiments, the means for selecting the first set of transmission layers may include means for selecting the first set of transmission layers such that a power increase due to feed-forward processing and feedback processing of a first set of reference signals to be transmitted over the first set of transmission layers is equal to or less than a power decrease of the first set of reference signals.

In some embodiments, an apparatus capable of performing method 500 comprises: means for receiving an indication of a first reference signal type for a first set of transmission layers to indicate that both feedback processing and feedforward processing have been performed on the first set of reference signals on the first set of transmission layers; means for receiving an indication of a second reference signal type for a second set of transmission layers to indicate that feedforward processing has been performed on the second set of reference signals on the second set of transmission layers without performing feedback processing on the second set of reference signals; means for receiving a first set of transport layers and a second set of transport layers simultaneously; and means for decoding the first set of transport layers and the second set of transport layers according to the first indication and the second indication.

In some embodiments, the means for decoding the first set of transport layers and the second set of transport layers may comprise: means for performing channel estimation and interference estimation for a first set of layers based on a first set of reference signals; means for performing channel estimation on a second set of layers based on a second set of reference signals while avoiding interference estimation; means for decoding the first set of layers using a minimum mean square error receiver; and means for decoding the second set of layers using a maximum ratio combining receiver.

In some embodiments, the means for decoding the first set of transport layers and the second set of transport layers may comprise: means for inverting the predefined power backoff for the first set of transmission layers while avoiding inverting the predefined power backoff for the second set of transmission layers.

Fig. 10 is a simplified block diagram of a device 1000 suitable for implementing embodiments of the present disclosure. The apparatus 1000 may be implemented at the transmitter 210 as shown in fig. 2, or as at least a portion of the transmitter 210 as shown in fig. 2.

As shown, the device 1000 includes a processor 1010, a memory 1020 coupled to the processor 1010, a communication module 1030 coupled to the processor 1010, and a communication interface (not shown) coupled to the communication module 1030 having a plurality of antennas (not shown). The memory 1020 stores at least a program 1040. The communication module 1030 is used for bidirectional communication. The communication interface may represent any interface necessary for communication.

The programs 1040 are assumed to include program instructions that, when executed by the associated processor 1010, enable the device 1000 to operate in accordance with embodiments of the present disclosure, as discussed herein with reference to fig. 2-9. The embodiments herein may be implemented by computer software executable by the processor 1010 of the device 1000, or by hardware, or by a combination of software and hardware. The processor 1010 may be configured to implement various embodiments of the present disclosure.

The memory 1020 may be of any type suitable to the local technology network and may be implemented using any suitable data storage technology, such as non-transitory computer-readable storage media, semiconductor-based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory, as non-limiting examples. Although only one memory 1020 is shown in device 1000, there may be several physically distinct memory modules in device 1000. The processor 1010 may be of any type suitable for a local technology network, and may include one or more of the following, as non-limiting examples: general purpose computers, special purpose computers, microprocessors, Digital Signal Processors (DSPs) and processors based on a multi-core processor architecture. Device 1000 may have multiple processors, such as application specific integrated circuit chips that are time dependent from a clock synchronized to the main processor.

All operations and features related to the transmitter 210 and receiver 220 described above with reference to fig. 2-9 are equally applicable to the device 1000 and have similar effects. Details will be omitted for the sake of simplicity.

In general, the various embodiments of the disclosure may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. Some aspects may be implemented in hardware, while other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device. While various aspects of the embodiments of the disclosure are illustrated and described as block diagrams, flow charts, or using some other pictorial representation, it is well understood that the blocks, apparatus, systems, techniques or methods described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.

The present disclosure also provides at least one computer program product tangibly stored on a non-transitory computer-readable storage medium. The computer program product comprises computer-executable instructions, such as included in program modules, that are executed in a device on a target real or virtual processor for performing the

methods

300 and 500 described above with reference to fig. 2-9. Generally, program modules include routines, programs, libraries, objects, classes, components, data structures, etc. that perform particular tasks or implement particular abstract data types. In various embodiments, the functionality of the program modules may be combined or divided between program modules. Machine-executable instructions for program modules may be executed within local or distributed devices. In a distributed facility, program modules may be located in both local and remote memory storage media.

Program code for performing the methods of the present disclosure may be written in any combination of one or more programming languages. These program codes may be provided to a processor or controller of a general purpose computer, special purpose computer, or other programmable data processing apparatus, such that the program codes, when executed by the processor or controller, cause the functions/operations specified in the flowchart and/or block diagram to be performed. The program code may execute entirely on the computer, partly on the computer, as a stand-alone software package, partly on the computer and partly on a remote computer or entirely on the remote computer or server.

In the context of the present disclosure, computer program code or related data may be carried by any suitable carrier to enable a device, apparatus or processor to perform various processes and operations as described above. Examples of the carrier include a signal, computer readable medium.

The computer readable medium may be a computer readable signal medium or a computer readable storage medium. A computer readable medium may include, but is not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples of a computer-readable storage medium would include an electrical connection having one or more wires, a portable computer diskette, a hard disk, a Random Access Memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing.

Further, while operations are depicted in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In some cases, multitasking and parallel processing may be advantageous. Also, while the above discussion contains several specific implementation details, these should not be construed as limitations on the scope of the disclosure, but rather as descriptions of features that may be specific to particular embodiments. Certain features that are described in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable subcombination.

Although the disclosure has been described in language specific to structural features and/or methodological acts, it is to be understood that the disclosure defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.

Various embodiments of the techniques have been described. Additionally or alternatively to the foregoing, the following examples are described. Features described in any of the examples below may be used with any of the other examples described herein.

Claims

1. An apparatus, comprising:

at least one processor; and

at least one memory including computer program code;

the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus to:

selecting, at a transmitter, a first set of transmission layers from a plurality of transmission layers via a plurality of antennas;

performing both feedback processing and feedforward processing on a first set of reference signals to be transmitted on the first set of transmission layers;

selecting, at the transmitter, a second set of transmission layers other than the first set of transmission layers from the plurality of transmission layers via the plurality of antennas;

performing the feed-forward processing on a second set of reference signals to be transmitted on the second set of transmission layers from the plurality of transmission layers while avoiding the feedback processing on the second set of reference signals; and

transmitting the first set of reference signals on the first set of transmission layers and simultaneously transmitting the second set of reference signals on the second set of transmission layers.

2. The apparatus of claim 1, wherein the at least one memory and the computer program code are further configured to, with the at least one processor, cause the apparatus to:

transmitting an indication of a first reference signal type on the first set of transmission layers to indicate that both the feedback processing and the feedforward processing have been performed on the first set of reference signals.

3. The apparatus of claim 1 or 2, wherein the at least one memory and the computer program code are further configured to, with the at least one processor, cause the apparatus to:

transmitting an indication of a second reference signal type on the second set of transmission layers to indicate that the feed-forward processing has been performed on the second set of reference signals without performing the feedback processing on the second set of reference signals.

4. The apparatus of any of claims 1-3, wherein each of the power of the first set of reference signals and the power of the second set of reference signals is reduced by a predetermined power level.

5. The apparatus of claim 4, wherein the at least one memory and the computer program code are further configured to, with the at least one processor, cause the apparatus to:

transmitting an indication of the predetermined power levels for the first set of transmission layers.

6. The apparatus of claim 4 or 5, wherein the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus to:

selecting the first set of transmission layers such that a power increase due to the feed-forward processing and the feedback processing of the first set of reference signals to be transmitted over the first set of transmission layers is equal to or less than a power decrease of the first set of reference signals.

7. A method, comprising:

8. The method of claim 7, further comprising:

9. The method of claim 7 or 8, further comprising:

10. The method of any of claims 7 to 9, wherein each of the power of the first set of reference signals and the power of the second set of reference signals is reduced by a predetermined power level.

11. The method of claim 10, further comprising:

12. The method of claim 10 or 11, wherein selecting the first set of transport layers comprises:

13. A computer readable storage medium having stored thereon a computer program which, when executed by a processor, causes the processor to perform acts comprising:

14. The computer-readable storage medium of claim 13, wherein the actions further comprise:

15. The computer-readable storage medium of claim 13 or 14, wherein the actions further comprise:

16. The computer-readable storage medium of any of claims 13 to 15, wherein each of the power of the first set of reference signals and the power of the second set of reference signals is reduced by a predetermined power level.

17. The computer-readable storage medium of claim 16, wherein the actions further comprise:

18. The computer-readable storage medium of claim 16 or 17, wherein selecting the first set of transport layers comprises:

19. An apparatus, comprising:

at least one processor; and

at least one memory including computer program code;

receiving an indication of a first reference signal type for a first set of transmission layers to indicate that both feedback processing and feedforward processing have been performed on a first set of reference signals on the first set of transmission layers;

receiving an indication of a second reference signal type for a second set of transmission layers to indicate that the feed-forward processing has been performed on a second set of reference signals on the second set of transmission layers without performing the feedback processing on the second set of reference signals;

receiving the first set of transport layers and the second set of transport layers simultaneously; and

decoding the first set of transport layers and the second set of transport layers according to the first indication and the second indication.

20. The apparatus of claim 19, wherein the at least one memory and the computer program code are further configured to, with the at least one processor, cause the apparatus to:

performing channel estimation and interference estimation for the first set of layers based on the first set of reference signals;

performing channel estimation for the second set of layers while avoiding interference estimation based on the second set of reference signals;

decoding the first set of layers using a minimum mean square error receiver; and

decoding the second set of layers using a maximum ratio combining receiver.

21. The apparatus of claim 19 or 20, wherein the at least one memory and the computer program code are further configured to, with the at least one processor, cause the apparatus to:

inverting the predefined power backoff for the first set of transmission layers while avoiding inverting the predefined power backoff for the second set of transmission layers.

22. A method, comprising:

23. The method of claim 22, wherein decoding the first set of transport layers and the second set of transport layers comprises:

decoding the second set of layers using a maximum ratio combining receiver.

24. The method of claim 22 or 23, wherein decoding the first set of transport layers and the second set of transport layers comprises:

25. A computer readable storage medium having stored thereon a computer program which, when executed by a processor, causes the processor to perform acts comprising:

receiving an indication of a first reference signal type of a first transmission group layer to indicate that both feedback processing and feedforward processing have been performed on a first group of reference signals on the first transmission group layer;

26. The computer-readable storage medium of claim 25, wherein decoding the first set of transport layers and the second set of transport layers comprises:

decoding the second set of layers using a maximum ratio combining receiver.

27. The computer-readable storage medium of claim 25 or 26, wherein decoding the first set of transport layers and the second set of transport layers comprises: