CN112154616B

CN112154616B - Transmission method

Info

Publication number: CN112154616B
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 Solutions and Networks Oy
Current assignee: Nokia Shanghai Bell Co Ltd; Nokia Solutions and Networks Oy
Priority date: 2018-05-22
Filing date: 2018-05-22
Publication date: 2023-07-14
Anticipated expiration: 2038-05-22
Also published as: CN112154616A; WO2019222913A1

Abstract

A transmission method, a user terminal device and a device configured to communicate with a set 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 a channel of a connection; finding (404) a precoding vector for a connection by maximizing a received power of the connection and minimizing interference of the connection to a previous connection; adding (406) a precoding vector to a feedforward filter; and obtaining (408) a feedforward 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 continually evolving. There is a continuing need for higher data rates and high quality services. 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 signal to be transmitted may be applied. The precoding may be linear or nonlinear. Nonlinear 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 present invention there is provided an apparatus for communication as described herein.

According to one aspect of the present invention, there is provided a method in a communication device as described herein.

Drawings

One or more examples of implementations are set forth in more detail in the figures and 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 a communication between a base station or access point and a set of user terminals;

fig. 3 illustrates an example of a signaling diagram related to a nonlinear precoding solution;

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

FIG. 7 illustrates an example of simulation results of 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 merely examples. Although the specification may refer to "an", "one", or "some" embodiment(s) in several locations, this does not necessarily mean that each such reference or feature is applicable to the same embodiment(s) only to a single embodiment. Individual features of different embodiments may also be combined to provide further embodiments. Furthermore, the words "comprise" and "comprising" should be understood not to limit the described embodiments to consist of only those features already mentioned, and such embodiments may also include features, structures, units, modules, etc. not specifically mentioned.

Hereinafter, 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 will be apparent to those skilled in the art that the embodiments can also be applied to other kinds of communication networks having suitable components by appropriately adjusting the parameters and programs. Some examples of other options for a suitable system 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), wireless access (WiMAX),

Personal Communication Services (PCS),)>

Wideband Code Division Multiple Access (WCDMA), systems using Ultra Wideband (UWB) technology, sensor networks, mobile ad hoc networks (MANET), and internet protocol multimedia subsystem (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 that shown. The connections shown in fig. 1 are logical connections; the actual physical connections may vary. 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 system given as an example, 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 equipments

100 and 102 configured to be in a wireless connection on one or more communication channels in a cell provided by an access node 104, such as an access point AP, (e/g) NodeB, distributed unit DU, relay node, in the embodiment shown in fig. 1 and for convenience of description denoted in the description by reference numeral 104. The physical link from the user equipment to the (e/g) NodeB is referred to as the uplink or reverse link, and the physical link from the (e/g) NodeB to the user terminal is referred to as the downlink or forward link. It should be appreciated that the (e/g) NodeB or its functionality may be implemented by using any node, host, server or access point entity suitable for such use.

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 via a wired or wireless link specifically designed for that purpose. These links may be used for data and signaling purposes. The (e/g) 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, access point, or any other type of interface device including a relay station capable of operating in a wireless environment. The (e/g) NodeB comprises or is coupled to a transceiver. A connection is provided from the transceiver of the (e/g) NodeB to the antenna unit, which connection establishes a bi-directional radio link to the user equipment. The antenna unit may comprise a plurality of antennas or antenna elements. The (e/g) NodeB is further connected to a core network 106 (CN or next generation core NGC). Depending on 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) for providing a connection of a User Equipment (UE) with an external packet data network, or a Mobility Management Entity (MME), etc.

A user terminal UT (also referred to as a UE, user equipment, terminal equipment, etc.) illustrates one type of apparatus that is allocated and assigned resources on the 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-backhaul relay) directed to a base station.

A user terminal generally refers to a portable computing device that includes a wireless mobile communications device that operates 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, gaming machines, notebook computers, and multimedia devices. It should be appreciated that the user terminal may also be a nearly exclusive upstream-only device, an example of which is a camera or video camera that loads images or video clips into 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 through the network without requiring person-to-person or person-to-computer interaction. The user terminal may also utilize the cloud. In some applications, the user terminal may comprise a small portable device with radio parts (such as a watch, headphones or glasses) and the computation is performed in the cloud. The user terminal (or in some embodiments, the layer 3 relay node) is configured to perform one or more of the user equipment functionalities. A user terminal may also be called a subscriber unit, mobile station, remote terminal, access terminal, or User Equipment (UE) to mention just a few names or means.

The various techniques described herein may also be applied to the information physical system (CPS) (a system of computing elements cooperatively controlling physical entities). CPS can 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 information physical systems of which the physical system in question has an inherent mobility are sub-categories of information physical systems. 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 (so-called small cell concept), including macro sites that operate in cooperation with smaller stations and employ 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 video streaming, augmented reality, different ways of data sharing, and various forms of machine-like applications such as (large-scale) machine-like communications (mctc), including vehicle security, different sensors, and real-time control. It is expected that 5G has 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 early stages, integration with LTE can be implemented as a system providing macro coverage by LTE, and by aggregating to LTE,5G radio interface access from small cells. In other words, 5G plans support 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, in which multiple independent and dedicated virtual subnets (network instances) can be created within the same infrastructure to run services with different requirements on latency, reliability, throughput and mobility.

The current architecture in LTE networks is fully distributed in the radio and fully centralized in the core network. Low latency applications and services in 5G require content to be brought close to the radio, resulting in local breakout and multi-access edge computation (MEC). 5G allows analysis and knowledge generation to take place at the data source. This approach requires the utilization of resources such as laptop computers, smartphones, tablet computers and sensors that may not be continuously connected 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 up response time. 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, but can also be categorized 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 (mass 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 other networks, such as a public switched telephone network or the internet, or with services provided by them, such as the IP/server, data storage 112 shown in fig. 1. The communication network may also be capable of supporting the use of cloud services, for example, at least a portion of the core network operations may be performed as cloud services (this is depicted in fig. 1 by the "cloud" 114). The communication system may also comprise a central control entity or the like providing facilities for networks of different operators to cooperate, for example in spectrum sharing.

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

It should also be appreciated that the labor allocation between core network operation and base station operation may be different from 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. The 5G (or new radio NR) network is designed to support multiple hierarchies, where MEC servers can be placed between the core and the base station or nodeB (gNB). It should be appreciated that MEC may also be applied to 4G networks.

In embodiments, 5G may also utilize satellite communications to enhance or supplement coverage of 5G services, for example, by providing backhaul. Possible use cases are to provide service continuity for machine-to-machine (M2M) or internet of things (IoT) devices or on-board passengers, or to ensure service availability for critical communications as well as future rail/maritime/aviation communications. Satellite communications may utilize Geostationary Earth Orbit (GEO) satellite systems, or Low Earth Orbit (LEO) satellite systems, particularly giant constellations (systems in which hundreds of (nano) satellites are deployed). Each satellite 110 in the jumbo constellation may cover several satellite-enabled network entities creating a ground cell. A terrestrial cell may be created by a 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 system depicted is merely an example of a portion of a radio access system, and in practice the system may comprise a plurality (e/g) of nodebs, a user equipment may access a plurality of radio cells, and the system may also comprise other means of at least one (e/g) NodeB, such as physical layer relay nodes or other network elements, etc., or may be a home (e/g) NodeB. Additionally, in a geographical area of the radio communication system, a plurality of different kinds of radio cells as well as 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 multiple (e/g) nodebs are required to provide such a network structure.

To meet the need for improved deployment and performance of communication systems, the concept of "plug and play" (e/g) nodebs has been introduced. In general, 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), typically installed within an operator network, may aggregate traffic from a large number of HNBs back to the core network.

As mentioned, an antenna array having 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 independent data signals in a given direction using a beam.

In embodiments, the sub-arrays of the set of sub-arrays may partially 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 a multi-user multiple-input multiple-output MU-MIMO transmission, a network element (such as, for example, a gmodeb) transmits signals to a plurality of user terminals using a plurality of 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 include one or more layers.

Precoding may be used to modify layer signals (layer signals) prior to transmission. Nonlinear precoding can mitigate inter-user interference better than linear precoding and is therefore an attractive implementation. For example, there is more than one variation for nonlinear precoding, such as Dirty Paper Coding (DPC) and Tomlinson-Harashima precoding (THP). DPC is known to be capable of capacity but it requires high-dimensional symbol-level processing with very high complexity. In contrast, THP is a lower complexity option for nonlinear 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 feedback filter 202 and modulo unit 204, which limit the power of symbols 206 to be transmitted. The symbols are further processed in a feed forward filter 208 for the purpose of triangulating the effective channel. In an embodiment, triangulating the effective channel means that the effective channel H can be used ^eff Modeled as a lower triangular matrix. Thus, the first and second substrates are bonded together,

wherein H is ^eff (i, j) is H ^eff The ith row and jth column element of (c).

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 modulus unit 212 from which the symbols of each layer of the user terminal signal are brought to a demodulator (not shown).

For downlink MIMO transmission, signals from multiple transmitter antennas are combined by receive filters 210. When linear precoding is used, the receive filter may be fully 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 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 receive filter to use. The signaling overhead must be low because the optimal receive filter will vary from channel to channel. Second, how to optimize THP performance when it is desired to design the receive filter, taking into account the low signaling overhead and low complexity requirements.

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 the access point. If the user terminal supports more than one reception mode, the base station or the access point may transmit a command to the user terminal to use the MRC. The 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 feed forward filter determination method is presented. The proposed filter ensures that the effective channel is triangulated under the limitations of using MRC receivers. In addition to reducing overhead, the performance of the proposed algorithm can also be verified over other NLP proposals by link-level and system-level simulations. The base station or access point may also obtain information about the appropriate receive filter for the user when determining the feed forward filter.

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

Fig. 3 illustrates an example of a signaling diagram related to the proposed non-linear precoding solution. The figure illustrates signaling 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 nonlinear 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 DMRS or codebooks may also be supported by extending the receiver mode indicator.

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

Wherein the method comprises the steps of

Channel estimated by user terminal j' through DMRS of layer i, and M _R Is 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 can well align the receiver's hypotheses between the base station or access point and the user terminal without any ambiguity, assuming that the base station or access point and the user terminal both know the channel from each transmission layer/port to each receive antenna at the user terminal. This may be achieved by having the necessary high resolution channel state information CSI for non-linear precoding 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 mode supported by the user terminal.

After transmitting the indicator 300, the base station or access point may be configured to perform 302 feedforward filter calculations and perform symbol generation. In conjunction with the feedforward filter computation, 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 performs scaling and modulo operations and demodulation 306 using the MRC received signal. Modulo arithmetic involves the use of THP.

In an embodiment, for use of the MRC receiver in the user terminal, the corresponding feedforward filter may be designed to triangulate the effective channel between the receiving layer and the transmitting layer. The effective channel may be defined as

H ^eff ＝W*HF，

Here the number of the elements is the number,

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

And represents a conjugate transpose.

Further, W mayExpressed as w=diag (W ₁ ，W ₂ ，...W _N ) Wherein

Is the receive filter of the user terminal n

K _n Is the number of layers of the user terminal n.

Is the physical channel from all receive antennas to all transmit antennas, where

M _T Is 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 set 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 group 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, this 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 a connection to be processed is to be transmitted.

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

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

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 feedforward filter when all connections have been processed.

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

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

MRC receiver->

Wherein M is _T Is the number of transmitter antennas per user terminal, and M _R Is 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 a previous connection. In other words, the feedforward filter is selected to maximize the received power of layer i and minimize interference of layer i with upstream layer 1, 2. For each upstream layer, an MRC receiver is assumed when calculating the interference.

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

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

In step 500, the apparatus is configured to initialize a determination by scheduling K layers for communication with a user terminal. For feedforward filter F and combined channel H ^pc Space is reserved. The first layer is selected for investigation or the layer index i is set to i=1.

In step 504, the apparatus is configured to determine whether all layers (i > K) have been processed. If so, a 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 reduce the value of |H by minimizing ^pc Each element of v% and make H _n v maximizing to determine a precoding vector for layer i, where H _n Is 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 weight factor w of 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 _n Is attached to matrix H _pc 。

In step 514, the apparatus is configured to add the determined precoding vector v to the feedforward filter as f= [ F, v ]. Thus, v is appended to matrix F as the last column. In addition, the layer index i is updated by i=i+1;

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

Fig. 6 illustrates an embodiment for determining that iterations of the feedforward filter are performed by each user terminal. At the same time, MRC receive filter properties may be obtained.

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

In step 602, the apparatus is configured to determine whether all user terminal layers have been processed (N > N). If so, a 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, channel state information is utilized in a normal manner to obtain data related to a 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 the user terminal n.

In step 610, the apparatus is configured to add the pre-coding filter values to the feedforward filter such that the temporary feedforward filter includes the pre-coding filter and the null space calculated so far.

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

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

In iteration round n, a temporary feedforward filter matrix F containing precoding vectors for user terminal 1,2,..n-1 _n-1 Are already known. The apparatus first projects the channel of user terminal n to F _n-1 To obtain the zero space of (2)

Wherein the method comprises the steps of

Is the physical channel of the user terminal n.

SVD (singular value decomposition) is then applied to decompose the projected channels, i.e.,

wherein the method comprises the steps of

And->

Is unitary matrix

Is a rectangular diagonal matrix of singular values.

Here, V is _n Front K of (1) _n Columns are used as precoding vectors for user terminal n and they are added to the feedforward filter, i.e., F _n ＝[F _n-1 V _n (：，1：K _n )]. When all user terminals have been processed, a complete feedforward filter F is obtained comprising precoding vectors of all layers of all user terminals. It is guaranteed by the projection operation with orthogonal columns for SVD and F.

It can be demonstrated that the MRC receiver of user terminal n is only U _n Front K of (1) _n Columns. Estimated channel for user terminal n from DMRS

Due to

And V _n (：，1：K _n ) Is orthogonal, thus simplifying

S _n Is 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 user terminal n is

S _n (1：K _n ，1：K _n ) Is diagonal, thus K of user terminal n _n There is no interlayer interference between the layers.

The combined effective channel for all user terminals is therefore lower 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 receiving layer of user terminal j is

Since j < n, V _j (：，1：K _j ) Or F _j-1 Is F _n-1 Sub-arrays of (2), thus with V _n (：，1：K _n ) Orthogonal. Thus (2)

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

By taking into account the trade-off between interference and received power, the method of each layer iteration allows some residual interference. H ^eff Allowing to include some small digits instead of 0.

In the iterative approach of 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 limit. Thus, this results in a strict lower triangular effective channel.

Fig. 7 illustrates link-level simulation results of an embodiment. Here, ideal CSI is assumed at a base station or an 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 of each user terminal in line-of-sight condition. Line 702 illustrates the linear precoding with zero forcing based on maximum SINR at the non-line-of-sight connection, and line 706 illustrates the proposed method with iteration of each user terminal in the non-line-of-sight condition, respectively. It can be seen that the throughput of the proposed solution is higher than that of linear precoding in both line-of-sight and non-line-of-sight channels.

The flow chart of fig. 8 illustrates 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 a demodulation reference signal, DMRS, and a data transmission comprising more than one layer, e.g. from a network element, such as a base station or an access point. These signals have been precoded at the transmitter by a feedforward filter.

In step 802, the apparatus is configured to determine channel properties based on a demodulation reference signal. Thus obtaining a channel estimate of the target signal (channel associated with the user terminal that is the target of 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 process 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 the interference. This may be performed based on the demodulation reference signal DMRS.

In step 808, the apparatus is configured to obtain a layer-by-layer estimate of the feedback weight of the user in the transmission of the data signal based on the interference from the upstream layer being zero after the 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 signal power and minimizing interference power.

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

Thus, the user terminal can detect precoded interference channels (upstream and downstream) from the DMRS. The precoded interfering channels implicitly include the effects from the feedforward 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 interference channels and obtain a better combiner than the 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 figures illustrate simplified examples of devices 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 104.

It should be understood that the apparatus is depicted herein as an example illustrating some embodiments. It will be apparent to those skilled in the art that the device may also include other functions and/or structures, and that not all of the described functions and structures are required. Although the apparatus has been depicted as one entity, the 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 having several physical entities located in 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. In addition, the memory may store software or applications 904 executable 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 the 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 device to one or more network elements of a communication network or system or the internet.

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

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. In addition, 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. Applications may be stored in 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 apparatus may further comprise a user interface 1010, the user interface 1010 being operatively connected to the control circuitry 1000 to enable a user to control and use the apparatus.

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

The steps and associated functions described above and in the figures that follow are not in absolute time order, and some steps may be performed simultaneously or in a different order than the given order. Other functions may also be performed between steps or within steps. Certain steps may be omitted or replaced with corresponding steps.

The apparatus or controller capable of performing the above steps may be implemented 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 many micro instructions for basic operations. The implementation of the microinstructions may vary depending on the CPU design. The computer program may be encoded 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 assembler). The electronic digital computer may also have an operating system that may provide system services to a computer program written in 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 analog and/or digital circuitry only, and (b) combinations of circuits and software (and/or firmware), such as (if applicable): (i) A combination of processor(s), or (ii) a portion of processor/software, including digital signal processor(s), software, and memory(s) that work together to cause the device 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 a portion 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' will also cover an implementation of only a processor (or multiple processors) or a portion of a processor and its (or their) accompanying software and/or firmware. For example and if applicable to a particular element, the term 'circuitry' would also cover a baseband integrated circuit or applications processor integrated circuit for a mobile phone or similar integrated circuit in a server, a cellular network device, or another network device.

An embodiment provides a computer program comprising instructions for causing an apparatus to perform the above embodiments.

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

The computer program may be in source code form, object code form or some intermediate form and it may be stored in some carrier (which may be any entity or device capable of carrying the program). Such carriers include, for example, recording media, computer memory, read-only memory, and software distribution packages. The computer program may be executed in a single electronic digital computer, or it may be distributed among multiple computers, depending on the processing power required.

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

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 a channel of a connection; means for finding a precoding vector for a connection by maximizing the received power of the connection and minimizing interference of the connection to a previous connection; means for adding the precoding vector to the feedforward filter; and means for obtaining a feedforward 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 signals; means for determining a maximum ratio combining parameter based on the channel information; means for determining channel information for interference based on the 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 a combination of 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 for communication 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 are 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 interference of the connection to a previous connection;

adding the precoding vector to a feedforward filter; and

obtaining the feedforward filter when all connections have been processed;

wherein the apparatus further comprises a transmitter configured to transmit to each user terminal in the set using one or more layers; the at least one memory and the computer program code are 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 feedforward filter; and

when all layers have been processed, the feedforward filter is obtained.

2. 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 about a channel of the user terminal;

projecting a channel of a user terminal to a null space of the feedforward filter;

decomposing the projected channel by using a single value to obtain a precoding filter value for the user terminal;

adding the pre-coding filter value to a feedforward filter, whereby the feedforward filter includes the pre-coding filter and a null space calculated so far; and

when all user terminals have been processed, the feedforward filter is obtained without a null space.

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

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

4. 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 to further:

the obtained feedforward filter is applied to the signal to be transmitted before transmission.

5. The apparatus of any of claims 1-4, the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus additionally to:

transmitting a command to those user terminals of the set of user terminals that support more than one reception mode to utilize a maximum ratio combining mode when data of the user terminals is received.

6. An apparatus for communication configured to communicate with a network element, the apparatus comprising

At least one processor;

at least one memory including computer program code;

receiving demodulation reference signals and data transmissions 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 weights;

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

combining the data signals is performed using the determined combiner parameters.

7. A method for a communication device configured to communicate with a set of user terminals, the method comprising, for each connection in a transmission from the device 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 feedforward filter; and

obtaining the feedforward filter when all connections have been processed;

wherein the method further comprises

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

determining the user terminal to which the layer is transmitted;

adding the precoding vector to a feedforward filter; and

when all layers have been processed, the feedforward filter is obtained.

8. The method of claim 7, further comprising:

for each user terminal:

obtaining information about a channel of the user terminal;

9. The method of claim 8, further comprising:

10. The method of claim 7, further comprising:

11. The method of any of claims 7 to 10, further comprising:

12. A method for a communication device configured to communicate with a network element, the method comprising:

determining channel properties based on the demodulation reference signals;

13. A computer readable medium having stored thereon instructions for causing an apparatus to perform the method according to any one of claims 7 to 12.