CN112154616A

CN112154616A - Transmission method

Info

Publication number: CN112154616A
Application number: CN201880093678.5A
Authority: CN
Inventors: 邵叙宁; E·维索特斯基; F·福克; 宋暖
Original assignee: Nokia Shanghai Bell Co Ltd; Nokia Networks Oy
Current assignee: Nokia Shanghai Bell Co Ltd; Nokia Oyj
Priority date: 2018-05-22
Filing date: 2018-05-22
Publication date: 2020-12-29
Anticipated expiration: 2038-05-22
Also published as: CN112154616B; WO2019222913A1

Abstract

A transmission method, user terminal apparatus and apparatus configured to communicate with a group of user terminals are disclosed. For each connection in a transmission from a device to the set of user terminals, the method comprises: determining (400) a user terminal to which the connection is transmitted; obtaining (402) information about connected channels; finding (404) a precoding vector for a connection by maximizing a received power of the connection and minimizing an interference of the connection to a previous connection; adding (406) the precoding vector to a feedforward filter; and obtaining (408) a feed forward filter when all connections have been processed.

Description

Transmission method

Technical Field

The exemplary and non-limiting embodiments relate to a transmission method in a communication system.

Background

Wireless telecommunication systems are constantly evolving. Higher data rates and high quality of service are always required. One solution to achieve the desired criteria in the downlink direction from the base station to the user terminal is to utilize multi-user multiple-input multiple-output MU-MIMO transmission. To improve MU-MIMO transmission, precoding the signals to be transmitted may be applied. The precoding may be linear or non-linear. Non-linear precoding can mitigate inter-user interference better than linear precoding and is therefore an attractive implementation.

Disclosure of Invention

The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the invention. It is not intended to identify key/critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later.

According to one aspect of the invention, a device according to claims 1 and 7 is provided.

According to one aspect of the invention, a method according to claims 8 and 14 is provided.

Drawings

One or more examples of implementations are set forth in more detail in the accompanying drawings and the description below. Other features will be apparent from the description and drawings, and from the claims.

FIG. 1 illustrates an example of a communication system in which some embodiments of the invention may be applied;

fig. 2 illustrates an example of applying Tomlinson-Harashima precoding in communications between a base station or access point and a set of user terminals;

figure 3 illustrates an example of a signaling diagram related to a non-linear precoding solution;

fig. 4, 5 and 6 are flowcharts illustrating examples of embodiments;

FIG. 7 illustrates an example of simulation results for an example embodiment;

fig. 8 is a flow chart illustrating an example of an embodiment; and

fig. 9 and 10 illustrate simplified examples of devices to which some embodiments of the invention may be applied.

Detailed Description

The following embodiments are examples only. Although the specification may refer to "an", "one", or "some" embodiment(s) in several places, this does not necessarily mean that each such reference or feature to the same embodiment(s) applies to only a single embodiment. Individual features of different embodiments may also be combined to provide further embodiments. Furthermore, the terms "comprising" and "including" should be understood as not limiting the described embodiments to consist of only those features that have been mentioned, and such embodiments may also contain features, structures, units, modules, etc. that are not specifically mentioned.

In the following, different exemplary embodiments will be described using a radio access architecture based on long term evolution advanced (LTE-advanced, LTE-a) or new radio (NR, 5G) as an example of an access architecture to which the embodiments can be applied, however, the embodiments are not limited to such an architecture. It is obvious to a person skilled in the art that the embodiments can also be applied to other kinds of communication networks with suitable components, by suitably adapting the parameters and procedures. Some examples of other options for suitable systems are Universal Mobile Telecommunications System (UMTS) radio Access network (UTRAN or E-UTRAN), Long term evolution (LTE, same as E-UTRA), Wireless local area network (WLAN or WiFi), Worldwide Interoperability for Microwave Access (WiMAX),

Personal Communication Services (PCS),

Wideband code division multipleAddress (WCDMA), systems using ultra-wideband (UWB) technology, sensor networks, mobile ad hoc networks (MANETs), and internet protocol multimedia subsystems (IMS), or any combination thereof.

Fig. 1 depicts an example of a simplified system architecture, showing only some elements and functional entities, all logical units, the implementation of which may differ from what is shown. The connections shown in FIG. 1 are logical connections; the actual physical connections may differ. It will be apparent to those skilled in the art that the system will typically include other functions and structures in addition to those shown in fig. 1.

However, the embodiments are not limited to the systems given as examples, but a person skilled in the art may apply the solution to other communication systems providing the necessary properties.

The example of fig. 1 shows a portion of an exemplary radio access network.

Fig. 1 shows user terminals or

user equipment

100 and 102 configured to be in wireless connection on one or more communication channels in a cell provided by an access node (such as an (e/g) NodeB) 104. The physical link from the user equipment to the (e/g) NodeB is called an uplink or reverse link, and the physical link from the (e/g) NodeB to the user terminal is called a downlink or forward link. It should be appreciated that the (e/g) NodeB or functionality thereof may be implemented by using any node, host, server, or access point, etc. entity suitable for such usage.

A communication system typically comprises more than one (e/g) NodeB, in which case the (e/g) nodebs may also be configured to communicate with each other over wired or wireless links designed specifically for this purpose. These links may be used for data and signaling purposes. (e/g) a NodeB is a computing device configured to control radio resources of a communication system coupled thereto. The NodeB may also be referred to as a base station, an access point, or any other type of interface device that includes relay stations capable of operating in a wireless environment. (e/g) the NodeB includes or is coupled to a transceiver. The antenna unit is provided with a connection from the transceiver of the (e/g) NodeB, which establishes a bi-directional radio link to the user equipment. The antenna unit may comprise a plurality of antennas or antenna elements. (e/g) the NodeB is further connected to a core network 106(CN or next generation core NGC). According to the system, the counterpart on the CN side may be a serving gateway (S-GW, routing and forwarding user data packets), a packet data network gateway (P-GW) or a Mobility Management Entity (MME) for providing a connection of a User Equipment (UE) with an external packet data network, or the like.

A user terminal UT (also referred to as UE, user equipment, terminal equipment, etc.) illustrates one type of apparatus that allocates and assigns resources on an air interface, and thus any of the features described herein with a user terminal may be implemented with a corresponding apparatus such as a relay node. An example of such a relay node is a layer 3 relay (self-backhauling relay) directed to a base station.

User terminals generally refer to portable computing devices including wireless mobile communication devices operating with or without a Subscriber Identity Module (SIM), including but not limited to the following types of devices: mobile stations (mobile phones), smart phones, Personal Digital Assistants (PDAs), cell phones, devices using wireless modems (alarm or measurement devices, etc.), laptop and/or touch screen computers, tablet computers, game consoles, notebook computers, and multimedia devices. It should be appreciated that the user terminal may also be the almost exclusive uplink-only device, an example of which is a camera or video camera that loads images or video clips to the network. The user terminal may also be a device with the capability to operate in an internet of things (IoT) network, which is a scenario in which objects are provided with the capability to transfer data over a network without human-to-human or human-to-computer interaction. The user terminal may also utilize the cloud. In some applications, the user terminal may include a small portable device with radio parts (such as a watch, headset, or glasses), and the computing is performed in the cloud. The user terminal (or in some embodiments, a layer 3 relay node) is configured to perform one or more of the user equipment functionalities. A user terminal may also be referred to as a subscriber unit, mobile station, remote terminal, access terminal, or User Equipment (UE), to name a few names or devices.

The various techniques described herein may also be applied to Cyber Physical Systems (CPS) (systems that cooperatively control computing elements of a physical entity). The CPS may enable implementation and development of a large number of interconnected ICT devices (sensors, actuators, processors, microcontrollers, etc.) embedded in physical objects at different locations. The mobile infophysical system in question, which has an inherent mobility of the physical system, is a sub-category of the infophysical system. Examples of mobile physical systems include mobile robots and electronic products transported by humans or animals.

Additionally, although the apparatus is depicted as a single entity, different units, processors, and/or memory units (not all shown in fig. 1) may be implemented.

5G enables the use of multiple-input multiple-output (MIMO) antennas, many more base stations or nodes than LTE (the so-called small cell concept), including macro-stations operating in cooperation with smaller stations and employing multiple radio technologies depending on service requirements, use cases and/or available spectrum. 5G mobile communications support a wide range of use cases and related applications, including different ways of video streaming, augmented reality, data sharing, and various forms of machine-type applications such as (large-scale) machine-type communications (mtc), including vehicle safety, different sensors, and real-time control. 5G is expected to have multiple radio interfaces, i.e., below 6GHz, cmWave and mmWave, and may also be integrated with existing legacy radio access technologies (such as LTE). At least in the early stages, integration with LTE may be implemented as a system where macro coverage is provided by LTE and access is from small cells over an aggregated to LTE, 5G radio interface. In other words, the 5G plan supports inter-RAT operability (such as LTE-5G) and inter-RI operability (inter-radio interface operability, such as below 6GHz-cmWave, below 6 GHz-cmWave-mmWave). One of the concepts considered for use in 5G networks is network slicing, where multiple independent and dedicated virtual subnetworks (network instances) can be created within the same infrastructure to run services with different requirements on latency, reliability, throughput and mobility.

Current architectures in LTE networks are fully distributed in the radio and fully centralized in the core network. Low latency applications and services in 5G require the content to be brought close to the radio, resulting in local breakout and multiple access edge computing (MEC). 5G enables analysis and knowledge generation to be performed at the data source. This approach requires the utilization of resources such as laptops, smartphones, tablets and sensors that may not be able to connect continuously to the network. MECs provide a distributed computing environment for application and service hosting. It also has the ability to store and process content in the vicinity of cellular subscribers to speed response times. Edge computing covers a wide range of technologies such as wireless sensor networks, mobile data acquisition, mobile signature analysis, collaborative distributed peer-to-peer ad hoc networks and processes, and can also be classified as local cloud/fog computing and grid/mesh computing, dew computing, mobile edge computing, micro-clouds, distributed data storage and retrieval, autonomous self-healing networks, remote cloud services, augmented and virtual reality, data caching, internet of things (large-scale connectivity and/or latency critical), critical communications (autonomous vehicles, traffic safety, real-time analysis, time critical control, healthcare applications).

The communication system is also capable of communicating with, or making use of, other networks, such as the public switched telephone network or the internet 112. The communication network may also be capable of supporting the use of cloud services, e.g., at least a portion of the core network operations may be performed as a cloud service (this is depicted in fig. 1 by "cloud" 114). The communication system may also comprise a central control entity or the like, which provides facilities for networks of different operators to cooperate, e.g. in spectrum sharing.

Edge clouds may enter a Radio Access Network (RAN) by utilizing network function virtualization (NVF) and Software Defined Networking (SDN). Using an edge cloud may mean that access node operations will be performed at least in part in a server, host, or node that is operably coupled to a remote radio head or base station that includes a radio part. It is also possible that node operations will be distributed among multiple servers, nodes or hosts. The application of the clooud RAN architecture enables RAN real-time functions to be performed on the RAN side (in the distributed unit DU 104) and non-real-time functions to be performed in a centralized manner (in the centralized unit CU 108).

It should also be understood that the labor allocation between core network operation and base station operation may be different than LTE or even non-existent. Some other technological advances that may be used are big data and all IP, which may change the way the network is built and managed. A 5G (or new radio NR) network is designed to support multiple hierarchies, where MEC servers can be placed between the core and base stations or nodebs (gnbs). It should be appreciated that MEC may also be applied to 4G networks.

In embodiments, 5G may also utilize satellite communications, for example by providing backhaul, to enhance or supplement the coverage of 5G services. Possible use cases are to provide service continuity for machine-to-machine (M2M) or internet of things (IoT) devices or vehicle passengers, or to ensure service availability for critical communications as well as future rail/maritime/airline communications. Satellite communications may utilize Geostationary Earth Orbit (GEO) satellite systems, but also Low Earth Orbit (LEO) satellite systems, in particular giant constellations (systems deploying hundreds of (nanometers) satellites). Each satellite 106 in the giant constellation may cover several satellite-enabled network entities that create terrestrial cells. The terrestrial cell may be created by the terrestrial relay node 104 or by a gNB located on the ground or in a satellite.

It will be apparent to those skilled in the art that the depicted system is only an example of a part of a radio access system, and in practice the system may comprise a plurality of (e/g) nodebs, which the user equipment may access, and which may also comprise other devices of at least one (e/g) NodeB, such as physical layer relay nodes or other network elements, etc., or may be home (e/g) nodebs. Additionally, in a geographical area of the radio communication system, a plurality of radio cells of different kinds and a plurality of radio cells may be provided. The radio cells may be macro cells (or umbrella cells), which are large cells typically having a diameter of up to tens of kilometers, or small cells such as micro cells, femto cells, or pico cells. The (e/g) NodeB of fig. 1 may provide any kind of these cells. A cellular radio system may be implemented as a multi-layer network comprising several cells. Typically, in a multi-layer network, one access node provides one or more cells, and thus a plurality of (e/g) nodebs are required to provide such a network structure.

To meet the demand for improved deployment and performance of communication systems, the concept of "plug and play" (e/g) nodebs has been introduced. Typically, a network capable of using a "plug and play" (e/g) NodeB includes a home NodeB gateway or HNB-GW (not shown in fig. 1) in addition to a home (e/g) NodeB (H (e/g) NodeB). An HNB gateway (HNB-GW), which is typically installed within an operator's network, may aggregate traffic from a large number of HNBs back to the core network.

As mentioned, antenna arrays with multiple antennas may be utilized in modern wireless communication systems. In an embodiment, the antenna array comprises a set of phase sub-arrays, each phase sub-array comprising a set of antennas and each configured to transmit or receive an independent data signal in a given direction with a beam.

In embodiments, the sub-arrays in the set of sub-arrays may partly share the same antenna elements, such as power amplifiers, low noise amplifiers, variable gain amplifiers and/or phase shifters, or they may be completely independent sub-arrays.

In multi-user multiple-input multiple-output MU-MIMO transmission, a network element (such as, for example, a gbodeb) transmits signals to multiple user terminals using multiple antennas, antenna arrays, or antenna elements. Signals from multiple antennas, antenna arrays, or antenna elements may be represented as layers or streams. The number of layers is always less than or equal to the number of antennas or antenna elements. The transmission to a given user terminal may comprise one or more layers.

Precoding may be used to modify the layer signal (layer signal) prior to transmission. Non-linear precoding may mitigate inter-user interference better than linear precoding and is therefore an attractive implementation. For example, there is more than one variation for non-linear precoding, such as Dirty Paper Coding (DPC) and Tomlinson-Harashima precoding (THP). DPC is known to achieve capacity, but it requires high-dimensional symbol-level processing with very high complexity. In contrast, THP is a lower complexity option for non-linear precoding and has limited performance loss and is therefore more attractive for implementation.

Fig. 2 illustrates an example of applying THP in communications between a base station or access point 104 and a set of user terminals.

The input to the THP precoder is the original symbols 200 for each layer. The precoder performs successive symbol-level interference cancellation operations implemented with the feedback filter 202 and the modulo unit 204, which limits the power of the symbols 206 to be transmitted. The symbols are further processed in a feedforward filter 208 with the purpose of triangularizing the effective channel (triangularize). In an embodiment, triangulating the effective channel means that the effective channel H can be divided into^effModeled as a lower triangular matrix. Therefore, the temperature of the molten metal is controlled,

wherein H^eff(i, j) is H^effRow i and column j.

The symbols are transmitted over a channel to a group of user terminals. The user terminal comprises a receive filter 210 and a scaling and modulo unit 212, from which receive filter 210 and scaling and modulo unit 212 the symbols of each layer of the user terminal signal are brought to a demodulator (not shown).

For downlink MIMO transmission, the signals from multiple transmitter antennas are combined by receive filter 210. When linear precoding is used, the receive filter may be completely determined by the user terminal. However, the receive filter determined by the user terminal is no longer optimal for non-linear precoding, as the user terminal lacks the necessary knowledge to account for the interference pre-cancellation operations performed at the base station or access point. Instead, the base station is responsible for designing the receive filters and transmitter precoding applied by the user terminals. There are some challenges associated with this approach. First, how to inform the user terminal what reception filter to use. The signaling overhead must be low because the optimal receive filter varies according to the channel. Second, how to optimize the performance of THP when the receive filter needs to be designed, considering the requirements of low signaling overhead and low complexity.

In an embodiment, a new mode of non-linear precoding in a base station or access point is proposed. The proposed mode does not require any additional signaling for the receive filter. The user terminal applies the maximum ratio combining when receiving signals transmitted by the base station or access point. If the user terminal supports more than one reception mode, the base station or access point may transmit a command to the user terminal to use MRC. A user terminal may receive a reference signal from a base station or access point and estimate a channel based on the reference signal and utilize this information in MRC reception. In an embodiment, the reference signal is a demodulation reference signal, DMRS.

In an embodiment, a novel feedforward filter determination method is presented. The proposed filter ensures that the effective channel is triangulated under the constraints of using an MRC receiver. In addition to reducing overhead, the performance of the proposed algorithm can be verified by link-level and system-level simulations over other NLP proposals. In determining the feed forward filter, the base station or access point may also obtain information about the user's suitability for the receive filter.

Another benefit of the proposed algorithm is that it nulls inter-layer interference within each user terminal through linear feed forward and receive filters. Thus, non-linear successive interference pre-cancellation is only required for inter-user terminal interference. Compared to the conventional NLP process, which generates symbols sequentially from one layer to the next, the proposed algorithm has the advantage of supporting parallel symbol generation for multiple layers of one user terminal.

Fig. 3 illustrates an example of a signaling diagram related to the proposed non-linear precoding solution. The figure illustrates the signalling between a base station or access point 104 and a user terminal 100.

In an embodiment, the base station or access point 104 may be configured to transmit the non-linear precoding mode indicator 300 to the user terminal 100. The indicator controls how the user terminal derives the receive filter used by the terminal. In an embodiment, the indicator informs the user terminal to apply MRC in receiving data transmissions from the base station or access point. In embodiments, other receiver modes based on, for example, dual DMRSs or codebooks may also be supported by extending the receiver mode indicator.

If the MRC based mode is selected, the user terminal is suggested to use the MRC receiver to combine the signals received from the base stations or access points. In general, the normalized MRC receiver vector for layer i of user terminal j may be defined as

Wherein

User terminal j' channel estimated by DMRS of layer j, and M_RIs the number of receive antennas per user terminal.

Unlike other types of receivers, such as MMSE (minimum mean square error) or SIC (successive interference cancellation), MRC receivers do not rely on noise and interference estimates, and therefore the receiver's assumptions can be well aligned between the base station or access point and the user terminal without any ambiguity, provided that both the base station or access point and the user terminal know the channel from each transmission layer/port at the user terminal to each receive antenna. This can be achieved by non-linear precoding with the necessary high resolution of the channel state information CSI at the base station or access point and DMRS based channel estimation at the user terminal.

In an embodiment, the receiver mode indicator may be removed if the MRC receiver based mode is the only supported mode for the user terminal.

After transmitting the indicator 300, the base station or access point may be configured to perform 302 the feed forward filter calculation and perform symbol generation. In conjunction with the feedforward filter calculation, the properties of the receive filter of the user terminal may be obtained.

Next, the base station or access point performs data and DMRS transmission 304 to the user terminal.

The user terminal receives the signal using the MRC, performs scaling and modulo operations, and demodulates 306. The modulo operation involves the use of THP.

In an embodiment, in order to use the MRC receiver in a user terminal, the corresponding feed forward filter may be designed to triangulate the effective channel between the receive and transmit layers. An effective channel may be defined as

H^eff＝W*HF，

Here, the number of the first and second electrodes,

is a combined block diagonal receive filter for all user terminals, wherein

N is the number of co-scheduled user terminals,

k is the total number of layers, an

The expression "conjugate transpose".

Further, W may be represented as W ═ diag (W)₁，W₂，...W_N) Wherein

Is a reception filter of a user terminal n, an

K_nIs the number of layers of the user terminal n.

Is a physical channel from all receive antennas to all transmit antennas, wherein

M_TIs the number of base station antennas.

Is a feed forward filter for all layers.

The flow chart of fig. 4 illustrates an example of an embodiment in an apparatus. The apparatus may be, for example, a base station or an access point. The apparatus is configured to communicate with a group of user terminals. The user terminals may be co-scheduled. In an embodiment, at least some connections in the transmission from the apparatus to a set of user terminals are configured to perform the following steps of fig. 4.

In an embodiment, the process of FIG. 4 is performed separately from each layer. In an embodiment, the process is performed by each user terminal. The flowchart of fig. 4 illustrates an alternative and different embodiments are described later.

In step 400, the apparatus is configured to determine a user terminal to which to transmit a connection being processed.

In step 402, the apparatus is configured to obtain information about a connected channel. In an embodiment, the channel state information is utilized in the normal manner to obtain data related to the channel.

In step 404, the apparatus is configured to find a precoding vector for a connection by maximizing the received power of the connection and minimizing the interference of the connection to previous connections.

In step 406, the apparatus is configured to add a precoding vector to the feedforward filter; and

in step 408, the apparatus is configured to obtain a feed forward filter when all connections have been processed.

In an embodiment, the above steps are performed for each layer used in the communication from a base station or access point to a set of user terminals.

In an embodiment, each iterative pass of the process generates a feed-forward precoding vector for one layer i

And MRC receiver

Wherein M is_TIs the number of transmitter antennas per user terminal, and M_RIs the number of receive antennas.

In an embodiment, the precoding vector for a connection is determined by maximizing the received power of the connection and minimizing the interference of the connection to previous connections. In other words, the feedforward filter is selected to maximize the received power of layer i and minimize the interference of layer i on the upstream layers 1, 2.. i-1. For each upstream layer, the MRC receiver is assumed when calculating the interference.

The MRC receiver for layer i may be calculated from the channel and feedforward filter for layer i.

Fig. 5 illustrates an embodiment in which each layer performs an iteration.

In step 500, the apparatus is configured to initiate the determination by scheduling K layers for communication with the user terminal. For feedforward filter F and combined channel H^pcSpace is reserved. The first layer is selected for study or the layer index i is set to i-1.

In step 504, the apparatus is configured to determine whether all layers have been processed (i > K). Yes, the feedforward filter has been obtained, and the process ends.

If not, the apparatus is configured to determine a target user terminal for layer i in step 506.

In step 508, the apparatus is configured to minimize | H^pcEach element of v | and let | H_nv | | | maximization to determine a precoding vector for layer i, where H_nIs a channel associated with a user terminal that is the target of layer i.

In step 510, in an embodiment, the apparatus is configured to calculate the weighting factor w for layer i as

In step 512, the apparatus is configured to update the combined channel H_pc＝[H_pc；w＊H_n]. Thus, w^*H_nIs appended to the matrix H_pc。

In step 514, the apparatus is configured to add the determined precoding vector v to the feed forward filter as F ═ F, v. Therefore, v is appended to the matrix F as the last column. In addition, the layer index i is updated by i + 1;

in an embodiment, the steps of fig. 4 may be performed once for each user terminal. Thus, one user terminal is processed per iteration round.

Fig. 6 illustrates an embodiment in which iterations for determining the feedforward filter are performed by each user terminal. Meanwhile, MRC receive filter attributes may be obtained.

In step 600, the apparatus is configured to initiate the determination by scheduling N user terminals for communication with the apparatus. A temporary feedforward filter is created. The first user terminal is selected for study or the index n is set to 1 for the user terminal.

In step 602, the apparatus is configured to determine whether all user terminal layers (N > N) have been processed. Yes, the feedforward filter has been obtained, and the process ends.

If not, the apparatus is configured to obtain information about the channel of the user terminal n in step 604. In an embodiment, the channel state information is utilized in the normal manner to obtain data related to the channel.

In step 606, the apparatus is configured to project the channel of the user terminal n to the null space of the temporary feed-forward filter.

In step 608 the apparatus is configured to derive a precoding filter value for user terminal n using a single value decomposition on the projected channel.

In step 610, the apparatus is configured to add the pre-coding filter values to the feed-forward filter, such that the temporary feed-forward filter includes the pre-coding filter calculated up to now and the null space.

When all user terminals have been processed, a feed forward filter F is obtained.

Thus, in an embodiment, the apparatus is configured to iteratively determine the precoding and receiving filters for each user terminal, one user terminal per iteration round.

In iteration round n, a temporary feedforward filter matrix F containing precoding vectors for user terminals 1, 2.. n-1_n-1Are already known. The device first projects the channel of a subscriber terminal n to F_n-1To obtain a null space of

Wherein

Is the physical channel of the user terminal n.

Then, SVD (singular value decomposition) is applied to decompose the projected channels, that is,

wherein

And

is a unitary matrix, an

Is a rectangular diagonal matrix of singular values.

Here, V is_nFront K of_nColumns are taken as precoding vectors for user terminal n and added to the feed forward filter, i.e. F_n＝[F_n-1V_n(：，1：K_n)]. When all user terminals have been processed, a complete feed forward filter F is obtained comprising the precoding vectors of all layers of all user terminals. It is ensured by the projection operation where SVD and F have orthogonal columns.

It can be shown that the MRC receiver of the user terminal n is U only_nFront K of_nAnd (4) columns. The estimated channel of user terminal n from DMRS is

Due to the fact that

And V_n(：，1：K_n) Are orthogonal, thus simplifying

S_nIs diagonal, so the normalized MRC receive filter is only W_n＝U_n(：，1：K_n) Regardless of S_n. After application of the MRC receiver, the effective channel of the user terminal n is

S_n(1：K_n，1：K_n) Is diagonal, so K of user terminal n_nThere is no interlayer interference between layers.

The combined effective channel of all user terminals is therefore downward triangular, i.e., without interference from user terminal n to user terminal j,

the effective interference channel from the transmission layer of user terminal n to the reception layer of user terminal j is

Since j < n, V_j(：，1：K_j) Or F_j-1Is F_n-1Of (a) thus with V_n(：，1：K_n) Are orthogonal. Thus, it is possible to provide

Only zeros are included, which means that the effective channel is triangulated by using the feedforward filter F and the MRC receiver.

The per-layer iterative approach allows for some residual interference by taking into account the trade-off between interference and received power. H^effThe upper triangular portion of (a) allows some small numbers to be included instead of 0.

In the iterative method for each user terminal, the interference to the upstream layer is strictly zero, and the received power to the target layer is maximized under the zero-interference constraint. This therefore results in a strict lower triangular effective channel.

Fig. 7 illustrates link-level simulation results of an embodiment. Here, ideal CSI is assumed at the base station or access point. The signal-to-noise ratio SNR is represented on the x-axis and the obtained sum rate is represented on the y-axis. Line 700 illustrates a linear precoding with zero forcing based on maximum SINR at the line-of-sight connection, and line 704 illustrates the proposed method with iteration per user terminal in line-of-sight conditions. Line 702 illustrates the linear precoding with zero forcing based on maximum SINR at non line-of-sight connections, respectively, and line 706 illustrates the proposed method with iteration per user terminal under non line-of-sight conditions. It can be seen that the throughput of the proposed solution is higher than the throughput of linear precoding in both line-of-sight and non-line-of-sight channels.

Figure 8 is a flow chart illustrating an example of an embodiment in an apparatus. The apparatus may be a user terminal or a part of a user terminal. The apparatus is configured to communicate with a base station or an access point.

In step 800, the apparatus is configured to receive, for example, from a network element (such as a base station or access point), a demodulation reference signal, DMRS, and a data transmission comprising more than one layer. These signals have been precoded at the transmitter by a feed forward filter.

In step 802, the apparatus is configured to determine a channel property based on a demodulation reference signal. Thus obtaining a channel estimate of the target signal (channel associated with the user terminal targeted for the layer).

In step 804, the apparatus is configured to calculate a maximum ratio combining parameter based on the channel information of the target signal obtained above.

In an embodiment, when the user terminal employs MRC in reception, the procedure may continue directly in step 814. If the user terminal further adjusts the combiner, the process continues in step 806.

In step 806, the apparatus is configured to determine channel information for interference. This may be performed based on a demodulation reference signal, DMRS.

In step 808, the apparatus is configured to obtain a layer-by-layer estimate of the feedback weights of the users in the transmission of the data signal based on interference from upstream layers being zero after maximum ratio combining for each layer.

In step 810, the apparatus is configured to obtain interference information. Here, the above determined interfering channel information is combined with the estimated feedback weights from the previous step.

In step 812, the apparatus is configured to calculate interference rejection combiner parameters. Here, the channel estimate of the target signal determined in step 802 and the interference information from step 810 are used to strike a tradeoff between maximizing the signal power and minimizing the interference power.

In step 814, the apparatus is configured to perform a combining of the data signals using the determined combiner parameters.

Thus, the user terminal can detect the precoded interfering channels (upstream and downstream) from the DMRS. The precoded interfering channel implicitly includes contributions from the feed forward filter.

In an embodiment, the user terminal may be configured to reconstruct the complete interference information by combining the blindly estimated feedback weights and the precoded interfering channels and obtain a better combiner compared to MRC.

Thus, the user terminal may directly utilize the MRC combiner, or perform blind detection and adjust the combiner to a better combiner.

Fig. 9 illustrates an embodiment. The figure illustrates a simplified example of an apparatus 100 to which embodiments of the invention may be applied. In some embodiments, the apparatus may be, for example, a base station or an access point.

It should be understood that the apparatus is depicted herein as illustrating examples of some embodiments. It is obvious to a person skilled in the art that the device may also comprise other functions and/or structures, and that not all described functions and structures are required. Although the apparatus has been depicted as one entity, different modules and memories may be implemented in one or more physical or logical entities. For example, the apparatus may be implemented using cloud computing or distributed computing with several physical entities located at different locations but connected to each other.

The apparatus of this example includes control circuitry 900 configured to control at least a portion of the operation of the apparatus.

The apparatus may include a memory 902 for storing data. Further, the memory may store software or applications 904 that may be executed by the control circuitry 900. The memory may be integrated in the control circuitry.

The control circuitry 900 is configured to execute one or more applications. Applications may be stored in memory 902.

The apparatus may further include one or more

wireless interfaces

906, 908 operatively connected to the control circuitry 900. The wireless interface may be connected to one or more sets of antennas, antenna elements, or antenna arrays 910.

The apparatus may further include one or more interfaces 912 operatively connected to the control circuitry 900. The interface may connect the apparatus to one or more network elements of a communication network or system or the internet.

In an embodiment, an application 904 stored in memory 902 executable by control circuitry 900 may cause an apparatus to perform the embodiments described above.

Fig. 10 illustrates an embodiment. In some embodiments, the apparatus may be, for example, a user terminal, user equipment, or corresponding apparatus in communication with a base station or access point.

The apparatus of this example includes control circuitry 1000 configured to control at least a portion of the operation of the apparatus.

The apparatus may include a memory 1002 for storing data. Further, the memory may store software or applications 1004 that may be executed by the control circuitry 1000. The memory may be integrated in the control circuitry.

The control circuitry 1000 is configured to execute one or more applications. The application may be stored in the memory 1002.

The apparatus may further include one or more wireless interfaces 1006 operatively connected to the control circuitry 1000. The wireless interface may be connected to one or more sets of antennas, antenna elements, or antenna arrays 1008. For example, the wireless interface may be a transceiver controlled by control circuitry.

The device may further include a user interface 1012, the user interface 1012 being operatively connected to the control circuitry 800 to enable a user to control and use the device.

In an embodiment, an application 1004 stored in a memory 1002 executable by the control circuitry 1000 may cause the apparatus to perform the above-described embodiments.

The steps and associated functions described above and in the accompanying drawings are not in an absolute chronological order, and certain steps may be performed simultaneously or in a different order than that given. Other functions may also be performed between steps or within steps. Certain steps may also be omitted or replaced with corresponding steps.

The apparatus or controller capable of performing the above steps may be embodied as an electronic digital computer or circuitry, which may include a working memory (RAM), a Central Processing Unit (CPU), and a system clock. The CPU may include a set of registers, an arithmetic logic unit, and a controller. The controller or circuitry is controlled by a series of program instructions transferred from the RAM to the CPU. The controller may contain a number of microinstructions for basic operations. The implementation of the microinstructions may vary depending on the CPU design. The computer programs may be coded by a programming language, which may be a high-level programming language (such as C, Java, etc.) or a low-level programming language (such as a machine language or an assembler). The electronic digital computer may also have an operating system that may provide system services to a computer program written with the program instructions.

As used in this application, the term 'circuitry' refers to all of the following: (a) hardware-only circuit implementations, such as implementations in only analog and/or digital circuitry, and (b) combinations of circuits and software (and/or firmware), such as (if applicable): (i) a combination of processor(s), or (ii) a processor (s)/part of software, including digital signal processor(s), software, and memory(s) that work together to cause an apparatus to perform various functions, and (c) circuitry that requires software or firmware to operate, even if the software or firmware is not physically present, such as a microprocessor(s) or part of a microprocessor(s).

This definition of 'circuitry' applies to all uses of this term in this application. As yet another example, as used in this application, the term 'circuitry' would also cover an implementation of merely a processor (or multiple processors) or portion of a processor and its (or their) accompanying software and/or firmware. For example, and if applicable to the particular element, the term 'circuitry' would also cover a baseband integrated circuit or applications processor integrated circuit for a server, a mobile phone or similar integrated circuit in a cellular network device or another network device.

Embodiments provide a computer program comprising instructions for causing an apparatus to perform the above-described embodiments.

Embodiments provide a computer program embodied on a non-transitory distribution medium, comprising program instructions that, when loaded into an electronic apparatus, are configured to control the apparatus to perform the above-described embodiments.

The computer program may be in source code form, object code form, or in some intermediate form, and it may be stored on some carrier, which may be any entity or device capable of carrying the program. Such a carrier comprises, for example, a record medium, a computer memory, a read-only memory and a software distribution package. Depending on the required processing power, the computer program may be executed in a single electronic digital computer, or it may be distributed between a plurality of computers.

The apparatus may also be implemented as one or more integrated circuits, such as an application specific integrated circuit, ASIC. Other hardware embodiments are also possible, such as circuits built from separate logic components. A hybrid of these different embodiments is also possible. For example, when choosing the implementation method, the skilled person will consider the requirements set on the size and power consumption of the device, the necessary processing power, the production costs and the throughput.

An embodiment provides an apparatus configured to communicate with a set of user terminals, the apparatus comprising: for each connection in a transmission from a device to a set of user terminals: means for determining a user terminal to which to transmit a connection; means for obtaining information about connected channels; means for finding a precoding vector for a connection by maximizing a received power of the connection and minimizing an interference of the connection with a previous connection; means for adding a precoding vector to a feedforward filter; and means for obtaining a feed forward filter when all connections have been processed.

An embodiment provides an apparatus configured to communicate with a network element, the apparatus comprising: means for receiving a demodulation reference signal and a data transmission comprising more than one layer from a network element; means for determining channel properties based on the demodulation reference signal; means for determining a maximum ratio combining parameter based on the channel information; means for determining channel information for interference based on a demodulation reference signal; means for obtaining interference information by combining the interference channel information and the estimated feedback weights; means for calculating interference rejection combiner parameters using the channel properties and the interference information; and means for performing combining on the data signals using the determined combiner parameters.

It will be obvious to a person skilled in the art that, as technology advances, the inventive concept can be implemented in various ways. The invention and its embodiments are not limited to the examples described above but may vary within the scope of the claims.

Claims

1. An apparatus configured to communicate with a set of user terminals, the apparatus comprising

At least one processor;

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 at least to perform:

for each connection in a transmission from the apparatus to the set of user terminals:

determining the user terminal to which the connection is transmitted

Obtaining information about a channel of the connection;

finding a precoding vector for the connection by maximizing a received power of the connection and minimizing an interference of the connection to a previous connection;

adding the precoding vector to a feed-forward filter; and

the feed forward filter is obtained when all connections have been processed.

2. The apparatus of claim 1, comprising a transmitter configured to transmit to each user terminal in the group using one or more layers; the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus to further, for each layer:

determining the user terminal to which the layer is transmitted;

finding a precoding vector for the layer by maximizing the received power of the layer and minimizing interference of the layer to a previous layer, considering that a maximum ratio combination is assumed to be utilized in a user terminal;

adding the precoding vector to a feed-forward filter; and

the feed forward filter is obtained when all layers have been processed.

3. The apparatus of claim 1, the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus further to, for each user terminal:

obtaining information on a channel of the user terminal;

projecting a channel of a user terminal to a null space of the feed-forward filter;

utilizing a single value decomposition of the projected channel to obtain a precoding filter value for the user terminal;

adding the pre-coding filter values to a feed-forward filter, whereby the feed-forward filter comprises the pre-coding filter calculated up to now and a null space; and

obtaining said feed forward filter without null space when all user terminals have been processed.

4. The apparatus of claim 3, the at least one memory and the computer program code further configured to, with the at least one processor, cause the apparatus to additionally:

obtaining unitary matrices Un and Vn from the projected channels using a single value decomposition, wherein the precoding filter values for the user terminals are the first Kn columns of Vn, and the first Kn columns of Un correspond to properties of the maximal ratio combiner for the user terminals, where Kn is equal to the number of layers in the transmission to the user terminals.

5. The apparatus of any preceding claim, the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus to additionally:

applying the obtained feedforward filter to the signal to be transmitted before transmission.

6. The apparatus of any preceding claim, the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus to additionally:

transmitting a command to those user terminals of the group of user terminals that support more than one reception mode to utilize a maximum ratio combining mode when receiving data for the user terminals.

7. An apparatus configured to communicate with a network element, the apparatus comprising

At least one processor;

at least one memory including computer program code;

receiving a demodulation reference signal and a data transmission comprising more than one layer from the network element;

determining channel properties based on the demodulation reference signals;

determining a maximum ratio combining parameter based on the channel information;

determining channel information for interference based on the demodulation reference signal;

obtaining interference information by combining the interference channel information and the estimated feedback weight;

calculating interference rejection combiner parameters using the channel properties and the interference information; and

performing combining on the data signals using the determined combiner parameters.

8. A method in an apparatus configured to communicate with a set of user terminals, the method comprising, for each connection in a transmission from the apparatus to the set of user terminals:

determining the user terminal to which the connection is transmitted

Obtaining information about a channel of the connection;

adding the precoding vector to a feed-forward filter; and

the feed forward filter is obtained when all connections have been processed.

9. The method of claim 8, further comprising

Transmitting to each user terminal in the group using one or more layers; and for each layer:

determining the user terminal to which the layer is transmitted;

adding the precoding vector to a feed-forward filter; and

the feed forward filter is obtained when all layers have been processed.

10. The method of claim 8, further comprising:

for each user terminal:

obtaining information on a channel of the user terminal;

11. The method of claim 10, further comprising:

12. The method of any preceding claim 8 to 11, further comprising:

13. The method of any preceding claim 8 to 12, further comprising:

14. A method in an apparatus configured to communicate with a network element, the method comprising:

determining channel properties based on the demodulation reference signals;

15. A computer program comprising instructions for causing an apparatus to perform at least any one of the methods as claimed in claims 8 to 14.