WO2018162158A1

WO2018162158A1 - Network-assisted device-to-device relaying for high-reliability and low-latency communication

Info

Publication number: WO2018162158A1
Application number: PCT/EP2018/052819
Authority: WO
Inventors: Hubertus MUNZ; Junaid Ansari
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2017-03-07
Filing date: 2018-02-05
Publication date: 2018-09-13

Abstract

A method of wireless communication performed by a central management node (102) in a wireless communication system, comprising: - obtaining reliability and/or latency requirements for a communication that is to be transmitted in the wireless communication system; - selecting, based on the obtained reliability and/or latency requirements, a transmission scheme for the communication from a set of possible transmission schemes, wherein each of the set of possible transmission schemes is defined by a unique combination of one or more relay nodes (106), one or more frequencies, and one or more times to be utilized for redundant transmission of the communication in the system; and - providing the selected transmission scheme to devices (104; 106; 108) in the system such that the communication is transmitted according to the selected transmission scheme.

Description

NETWORK-ASSISTED DEVICE-TO-DEVICE RELAYING FOR HIGH-RELIABILITY AND LOW-LATENCY COMMUNICATION

Technical Field

The application relates to systems, methods, and apparatus for wireless communication, and in particular, for network-assisted device-to-device (D2D) relaying for high-reliability and low- latency communication in a wireless communication environment.

Background

Currently, one objective of fifth-generation (5G) wireless communication protocols and systems is the support of ultra-low latency and reliable machine-type communication (MTC), known as Critical-MTC (C-MTC) or Ultra Reliable Low Latency Communication (URLLC). Communications that fall under the purview of these particular protocols address the low latency and high reliability requirements of a subset of specific use-cases, such as industrial applications, smart grids, remote control of machines and devices, etc. To reach the communication reliability and/or latency metrics required in these use-cases, techniques for utilizing communication diversity in space, time, and frequency are presently utilized. In addition to these lower-layer mechanisms, data transmission scheduling techniques are presently employed in higher layers in the Long-Term Evolution (LTE) protocol stack (such as the media access control (MAC) and radio link control (RLC) layers) to improve reliability and reduce latency in one or more of the above-mentioned use-cases.

Though these techniques represent an improvement over traditional wireless signal transmission and data scheduling methods, relatively high numbers of packet retransmissions over a same frequency are required to maintain data transmission reliability across the network, causing increased communication latency in the system. This is caused, for instance, by certain MAC layer processes that are typically necessary for packet retransmission, including the required assignment of medium access resources for the retransmission- resources that are often not instantly available. Also, the rigid time structure required for LTE communication mandates that retransmissions span the duration of an entire transmission time interval (TTI), which is a relatively extended time period in view of upcoming 4G/5G standards. Because time especially critical in C-MTC use-cases, there simply may be not enough allocatable time available for an explicit retransmission in some examples. Furthermore, merely introducing duplicated packets at the MAC layer does not universally satisfy the Quality-of- Service (QoS) requirements in URLLC applications.

As highlighted above, existing communication systems (e.g., LTE systems) cannot fulfil the requirements of C-MTC application use cases, which demand both a high degree of reliability and aggressively low latency levels. Therefore, improved methods and apparatuses are needed to meet these high reliability benchmarks while fulfilling the communication latency directives of certain emerging wireless communication use-cases. Summary

It is an object of the present invention to improve methods and apparatuses to meet high reliability benchmarks while fulfilling the communication latency directives of certain emerging wireless communication use-cases. This object is achieved by the independent claims. Advantageous embodiments are described in the dependent claims.

According to a first aspect, a method of wireless communication performed by a central management node in a wireless communication system is provided. The method comprises the step of obtaining reliability and/or latency requirements for a communication that is to be transmitted in the wireless communication system. The method further comprises the steps of selecting, based on the obtained reliability and/or latency requirements, a transmission scheme for the communication from a set of possible transmission schemes, wherein each of the set of possible transmission schemes is defined by a unique combination of one or more relay nodes, one or more frequencies, and one or more times to be utilized for redundant transmission of the communication in the system, and providing the selected transmission scheme to devices in the system such that the communication is transmitted according to the selected transmission scheme.

According to a further aspect, a central management node in a wireless communication network is provided. The central management node comprising at least a processor and a memory, the memory containing instructions executable by the processor to perform the method of wireless communication in a wireless communication system, comprising the step of obtaining reliability and/or latency requirements for a communication that is to be transmitted in the wireless communication system. The method further comprises the steps of selecting, based on the obtained reliability and/or latency requirements, a transmission scheme for the communication from a set of possible transmission schemes, wherein each of the set of possible transmission schemes is defined by a unique combination of one or more relay nodes, one or more frequencies, and one or more times to be utilized for redundant transmission of the communication in the system, and providing the selected transmission scheme to devices in the system such that the communication is transmitted according to the selected transmission scheme.

According to a further aspect, a method performed by a relay device in wireless communication network is provided. The method comprises the step of obtaining channel quality information for at least one channel utilized by the relay device. The method comprises the further step of transmitting the channel quality information to a central management node of the wireless communication network, and receiving, from the central management node, a transmission scheme for receiving and/or transmitting a communication to one or more other devices of the system. The transmission scheme is selected by the central management node based on one or more of the channel quality information and/or reliability and/or latency requirements associated with the communication and the transmission scheme is selected from a set of possible transmission schemes, wherein each of the set of possible transmission schemes is defined by a unique combination of one or more relay nodes, one or more frequencies, and one or more times to be utilized for redundant transmission of the communication in the system. The method further comprises the step of transmitting and/or receiving the communication according to the received transmission scheme.

According to a further aspect, a relay device in a wireless communication network is provided. The relay device comprising at least a processor and a memory. The memory containing instructions executable by the processor to perform a method in wireless communication network. The method comprises the step of obtaining channel quality information for at least one channel utilized by the relay device. The method comprises the further step of transmitting the channel quality information to a central management node of the wireless communication network, and receiving, from the central management node, a transmission scheme for receiving and/or transmitting a communication to one or more other devices of the system. The transmission scheme is selected by the central management node based on one or more of the channel quality information and/or reliability and/or latency requirements associated with the communication and the transmission scheme is selected from a set of possible transmission schemes, wherein each of the set of possible transmission schemes is defined by a unique combination of one or more relay nodes, one or more frequencies, and one or more times to be utilized for redundant transmission of the communication in the system. The method further comprises the step of transmitting and/or receiving the communication according to the received transmission scheme.

The present invention also concerns computer programs comprising portions of software codes or instructions in order to implement the method as described above when operated by at least one respective processing unit of a user device and a recipient device. The computer program can be stored on a computer-readable medium. The computer-readable medium can be a permanent or rewritable memory within the user device or the recipient device or located externally. The respective computer program can also be transferred to the user device or recipient device for example via a cable or a wireless link as a sequence of signals.

Brief Description of the Figures

In the following, the invention will further be described with reference to exemplary embodiments illustrated in the figures, in which:

Fig. 1 illustrates a wireless communication system corresponding to example embodiments of the present disclosure,

Fig. 2 illustrates a graph comparing aspects of one or more embodiments of the present disclosure and legacy techniques,

Fig. 3 illustrates a method performed by a destination or receiving device according to one or more embodiments,

Fig. 4A and 4B illustrate aspects of communication relay aspects utilized in example embodiments of the present invention,

Fig. 5 illustrates resource allocation in bootstrapping and transmission phases of example embodiments of the present invention,

Fig. 6 illustrates example transmission schemes utilized under different example system conditions according to example embodiments of the present disclosure,

Fig. 7 illustrates aspects of a bootstrapping scheme performed in example embodiments of the present disclosure,

Fig. 8 illustrates a logical channel stack in some examples,

Fig. 9 illustrates different potential quality and latency constraints and appropriate transmission schemes to implement, Fig. 10 illustrates a method performed by a central management node according to one or more embodiments,

Fig. 11 illustrates a method performed by a relay device according to one or more embodiments,

Fig. 12a and 12b illustrate example components of a central management node according to one or more embodiments, and

Fig. 13a and 13b illustrate example components of a relay device according to one or more embodiments. Detailed Description

The present disclosure describes example techniques for transmitting reliable and low-latency wireless communications by utilizing particular time-frequency resources and relay devices selected by a central management node in a wireless communication system to provide redundant transmissions of the communications to a destination device. In an aspect, the central management node is configured to manage communication scheduling in the system, including selecting one or more relays, one or more frequencies, and one or more transmission times that together constitute a transmission scheme to be executed for transmission (e.g. an original source device transmission toward a receiving device), retransmission (a subsequent copy of the transmission sent by the source node later in time), relaying (i.e. a redundant transmission (a transmitted copy of the original source device transmission detected by a relay device), etc. of the communication in the system. In some examples, this transmission scheme selection may be based on past, present, or predicted channel conditions (e.g., reported by one or more relays or other system nodes), Quality of Service (QoS) requirements of the communication, and system device topology information. By utilizing the selected resources of the transmission scheme for executing a number of transmissions and sometimes retransmissions by the source device and/or relay transmissions to be conducted by one or more relay devices of the system, reliability of the transmission increases without the added latency associated with single-source device retransmission schemes (e.g. HARQ (Hybrid Automated Repeat ReQuest)).

In addition to selecting the particular relays (also referred to herein as relay nodes, nodes, relay devices, or the like) to perform the relay transmissions, the central management node can also select (again, based on obtained channel conditions and/or system topology information) one or more frequency and/or time resources to be used for the determined transmissions. Together with the selected relay devices, these chosen time and frequency resources form a transmission scheme that is selected by the central management node from a set of possible transmission schemes. In other words, the selected transmission scheme is defined by a unique combination of one or more relay nodes, one or more frequencies, and one or more times to be utilized for the communication.

By using channel condition and/or topology information (and/or device capabilities, available resources, and QoS requirements) as a basis for selecting the transmission scheme selected over the other available schemes, embodiments of the central management node described herein represent a viable solution to meeting the low latency and high reliability communication demands of forthcoming wireless communication standards and use-cases.

Fig. 1 illustrates, in each of three non-limiting examples 0.2ms time slots, three communication states during transmission (including one or more intermediate redundant transmissions, e.g., by one or more relays 106) of a communication from a source device 104 to a destination device 108 in a wireless communication system 100 (optionally referred to herein as simply "system 100"). The system 100 can include two or more devices configured to perform D2D (or loT, M2M) wireless communication such as, but not limited to, relays 106, which are configured to receive a wireless transmission from another device and subsequently transmit the same or a similar communication on to further devices (e.g., destination device 108).

In addition to the source device 104, destination device 108, and relays 106, the system 100 includes a central management node 102, which is configured to control and otherwise manage control and data channel communication scheduling for the devices 104, 106, 108 in system 100. Aspects of central management node 102 are discussed in further detail below.

In an example use-case, system 100 of Fig. 1 may represent an industrial automation system that runs industrial automation applications in an Industrial loT realization. Such a use-case is a natural fit because industrial automation applications and devices demand highly reliable communication with extremely low latency bounds. Industrial automation and control typically involves sensors (i.e. source device 104 or relay 106) that report data to a Programmable Logic Controller (PLC), which could embody the central management node 102 of Fig. 1. Based on sensory data, the PLC instructs an actuator, e.g., a robot, to perform a certain action, forming a control and feedback loop. These control scenarios are often regarded as highly stringent with robust and real-time data communication demands. For instance, in discrete manufacturing processes involving packaging machines, printing presses, and palletizing stations, the maximum communication latency requirement can be lower than 1 ms and reliability demand can be as high as affording only one transmitted message to be lost out of a billion transmissions (both being non-limiting examples).

Thus, in some embodiments contemplated herein, the communications transmitted according to a selected transmission scheme may be a critical communication in local cells (in the example presented above, these may be autonomous automation cells) carried out using network assisted D2D transmissions. In these embodiments, among others, time and frequency resources are allocated and otherwise managed by a central management node 102.

In a further aspect of the present disclosure, spatial diversity is leveraged for transmissions in the system 100. Installation of multiple antennas is not always possible, however, for devices utilized in automation and other D2D applications due to the small size of some D2D/loT/M2M devices (e.g., sensors, actuators, etc.), it could be necessary to make spatial diversity beneficial. To enable spatial diversity without implementing multiple antennas on each device, the presently described embodiments can utilize cooperative transmission schemes to introduce spatial diversity, which is particularly beneficial in systems that use communication between multiple devices organized in cells as e.g. in automation cells to boost reliability. In a further aspect of the present disclosure, these spatial diversity techniques may be combined with time and frequency resource diversity in a unique manner to support system needs, such as those of C-MTC systems. Cooperative communication, as frequency and time diversity is used to introduce redundant communication.

In an aspect, redundant transmission in space can be carried out by relaying packets via one or more relays 106 (also referred to as "relay nodes," and/or "relay devices") situated within a particular system 100. For purposes of this disclosure, redundant transmission refers to transmission of multiple copies or instances of a communication. In addition, for purposes of the present disclosure, the term "communication" refers to any data transmitted between devices, and may comprise one or more bits/bytes, a packet data unit, a packet, a message (data or control or otherwise), or any other form by which electronic content is known to be bundled and/or transmitted. In as aspect, and as shown in Fig. 1 , the relay nodes 106 can be devices with independent functionality and purpose, such as sensors, actuators, any loT device, processor, functional module, component, PLC, etc. which are part of the automation process, as well as dedicated nodes serving as relays. Furthermore, this cooperative relaying scheme can be particularly useful for critical links, such as those having URLLC requirements. Depending upon the particular URLLC requirements, the cooperative communication relaying can be configured and adapted at runtime in some example. For instance, varying and non-homogenous QoS requirements can be supported.

Returning to Fig. 1 , the depicted example embodiment illustrates a scenario whereby in the first timeslot (which in some non-limiting instances may have a 0.2ms duration, but this is not required), a communication f1 is transmitted by source device 104 directly to destination device 108. Further, f1 is overheard (dashed lines) by the relay nodes 106 and central management node 102, which also serves as a relay node 106 in this example. In the second timeslot, the communications, received during the first timeslot, are relayed f2 and f3 (also can be called "forwarded") to the destination device 108. Also during the second timeslot, the source device 104 retransmits an f4 communication that is effectively a copy of the f1 communication from the first timeslot. Next, in the third timeslot, f4 is again received and relayed (as f5 and f6) by both of relay nodes 106 (i.e. central management node 102 and relay node 106) to the destination device 108 in the third timeslot. Accordingly, by utilizing existing system devices (106 and 102) as relays, the system 100 facilitates not only quick communication transmission to meet QoS and/or latency demands of the system 100, but also adds reliability to the ultimate communication by configuring one or more relays 106 to provide redundant transmissions to the destination device 108 such that the communication is received multiple times (here, six) to bolster overall reliability of communication transmission.

Also, the example transmission scheme discussed above with respect to Fig. 1 can be classified as an amplify-and-forward (also called transparent) relaying scheme. In the amplify- and-forward relaying, a relay node does not check whether it has received a packet correctly before it is relayed. Instead, this relaying happens on the physical layer without being decoded/processed before relaying toward a destination device 108. As can be seen in Fig. 2, amplify-and-forward results in a faster communication transmission from a source device to a destination device compared to other paradigms illustrated in the figure, even when redundant communication transmissions are performed by relays to meet the URLLC reliability demands. With amplify-and-forward the receiver processing queue can be kept filled whereas with the other scheme decode-and-forward longer breaks of no transmissions occurs. As an additional advantage of this technique, amplify-and-forward can be readily implemented in LTE and NR networks simply by performing a software upgrade.

In some examples, the relaying illustrated in Fig. 1 is performed in a two-hop multi-branch manner - namely, a single relay link or multiple parallel relay links (effectively parallel to a direct link between the source device 104 and destination device 108) are used to increase the probability of a reliable transmission. Furthermore, the source device 104 (also called "the original transmitter" herein) can be used to perform multiple redundant (i.e. serial) retransmissions in time. Adding a further layer of reliability to the overall communication transmission, each of these source device 104 retransmissions can be relayed at the relay node(s) 106 that overhear each source device 104 retransmission. The result of this redundant communication transmission technique is that the destination device 108 receives multiple redundant copies of the same communication: those transmitted over the direct link (directly from the source device 104) and those redundant transmissions carried via relay links that, in many use-cases, exhibit an uncorrelated link outage probability. Ultimately, the destination device 108 processes all of the redundant communication copies until a determination is made that the communication has been correctly received and/or determines that the correctly received copy exhibits an acceptable degree of reliability (e.g., that is greater than a reliability threshold).

Figure 3 depicts a detailed example of a communication receiving and processing technique executed by a destination device 108 in the present embodiments. As shown, the destination device 108 can receive one or more transmissions, relayed transmissions or retransmissions over the direct link (e.g., in packet form in a non-limiting example), and with each redundant communication received (or portion thereof) it is determined if the packet is to be discarded or stored in memory (e.g., a physical layer (PHY) buffer or other memory device). These stored communications/packets can be passed to the MAC layer and/or remain on the PHY for decoding and other necessary processing. Once in proper form for integrity verification, the destination device 108 or a component thereof can perform an integrity check, such as a cyclic redundancy check (CRC) on the received and processed communication data. If the verification passes, the communication or portion thereof (e.g., a packet) can be passed to upper layers for further processing, and if verification fails, the communication or portion thereof can be discarded.

Returning to the redundant communication transmission techniques introduced above, Fig. 4A and 4B illustrate further implementation details of these techniques, and do so in a non-limiting automated manufacturing environment. Dashed lines in both figures stand for control messages, whereas continuous lines depict data messages. As shown in Fig. 4A, another example wireless communication system 400 includes two example source devices 104, two loT sensors that additionally serve as relays 106, a destination device 108 manifested as an example automated manufacturing machine, and a central management node 102. In an aspect of the present embodiments, the relaying/redundant transmission of overheard communication transmissions from source nodes 104 can occur in a centrally configured manner via aspects performed by the central management node 102. By implementing centralized control of the relaying aspects, system 400 is able to take advantage of the oftentimes immovable device installations as well as the predictable and static software, protocol, and instruction frameworks that are commonplace to devices/nodes in industrial automation cells.

Of particular relevance to the present disclosure, in some examples, the central management node 102 is charged with monitoring communication conditions in the system 400 as well as configuring the wireless communication policies and techniques implemented in the system 400. In example embodiments, this may include selecting a transmission scheme (also referred to as a "relay scheme" herein) that is to be utilized by all (or a subset of) system devices. The transmission scheme defines the nodes/relays 106 and time and/or frequency resources that are to be used for communication transmissions, including direct-link transmissions and retransmissions/redundant transmissions (including critical messages (URLLC messages) depending upon the specific desired QoS demands). Once a relay scheme is configured, it may be used for a relatively long period of time (in a semi-persistent manner) to guarantee reliability, especially for a critical link. This is e.g. applicable for industrial automation communication node deployment. As introduced above, in addition to selecting one or more relays to implement spatial diversity, the central management node 102 can be configured to select one or more frequency resources and one or more time resources to be utilized for original transmissions as well as redundant transmissions/retransmissions by a source device or relay. For purposes of the present disclosure, each of the one or more frequency resources defines a sub-band and each of the one or more time resources defines a particular time period (e.g., slot, subframe, frame, symbol, or any other time measure or unit) allocated for one or more communication transmissions. The term time-frequency resource refers to the combined frequency resource and time resource scheduled and/or utilized for one or more transmissions, effectively representing one or more resources, resource blocks, resource units, resource elements, or the like in a frequency-time grid of multi-carrier modulation systems known in the art.

The central management node 102 is configured to select (whether static, dynamic, or semi- static) a transmission scheme for communication transmissions in the system. In some embodiments, the selected relay scheme can define the following:

for every relay node:

which time-frequency resources it has to listen on

which time-frequency resources are used for relaying

for the destination device:

on which time-frequency resources it can expect the original message and all the retransmissions and relayed transmissions

for the source device:

time-frequency resources for initial transmissions and its own re-transmissions As illustrated in Fig. 4A and 4B, once selected, this information defining the transmission scheme (D2D scheduling information) is provided by the central management node 102 to the involved nodes (relays/devices) before the actual communication transmission(s) over the selected time-frequency resource(s) is initiated. In an aspect, this information can be provided to the central management node 102 via control messaging as shown in Fig. 5. This figure shows a time-frequency resource allocation and scheduling grid. In a first "Bootstrapping" phase (shown as "B" resources), the central management node 102 initiates a bootstrapping process, where other available nodes/devices in the cell are evaluated to determine whether they can be beneficial for the transmission scheme. In the execution phase a periodic relay scheme is used for transmitting information according to a relay scheme. In the example of Fig. 5 an original transmission (O) is executed. In the subsequent timeslots, re-transmissions (RT) are executed on the frequency bands f5, f2 and fn-2. Further, two relay nodes relaying the transmission on further carriers. The control messaging/information can be transmitted before the communication transmission according to the transmission scheme is initiated. Before selecting a transmission scheme for a wireless communication system.

The evaluation/determination can be conducted based on channel quality information or any other information indicating a throughput or transmission quality associated with one or more channels or sub-bands/component carriers, including by Channel State Information (CSI) feedback from the system nodes to the central management node 102. The channel quality information (e.g., CSI) is used to determine the large-scale characteristics of possible relay links, and furthermore whether there is a possible correlation between a relay link and the direct link (i.e. to detect nodes/relays that have almost the same radio channel and therefore would not introduce any diversity). This CSI feedback is illustrated in Fig. 4A and 4B. For some links, multiple channel quality metrics are obtained for precision (such as for a relay link, which consists of two segments: TX-relay and relay-RX). Ultimately, the central management node 102 can utilize this information garnered from the system nodes to identify particular relays and time-frequency resources that may be optimal for utilization in a selected transmission scheme.

The bootstrapping process is further illustrated in Fig. 7, which displays further details of a particular implementation scenario. For instance, during bootstrapping, the central management node 102 can move through multiple processing segments to garner information about system links, topology, available resources, etc., including a segment for calculating channel correlation. The bootstrapping phase can be quite long (e.g. more than a minute) and can still be sufficient as this time is negligible compared to the run-time afterwards. In the example embodiment of Fig. 7, two segments are depicted to establish a dual-hop relaying. In addition, Fig. 6 shows three non-limiting example system implementation scenarios where the system environment/channels exhibit varying levels of quality in terms of latency, carrier availability, and relay devices available to increase reliability of transmissions. On the left-hand relay scheme in Fig. 6 a scenario with many used carriers (f1 - fn-1 ) is depicted. At least 8 carriers are used to transmit the information to a receiving node. The original transmission (O) is executed on carrier f4 in a first timeslot. Further, six relayed transmissions (indicated with numbers 1 - 6) are executed in the subsequent timeslot via six relay nodes in parallel with a retransmission RT from the original node. In consequence the transmission is executed in the first two timeslots which results in a transmission with very low latency. This relay scheme can be used for ultra-latency critical transmissions in a scenario with many relay nodes and many available carriers. The relay scheme in the middle of Fig. 6 shows a transmission over many carriers (comparable to the left-hand scenario). However, only one relay or coop, node is used. The original transmission happens in the first timeslot. Four re-transmissions from the original node are executed in some subsequent timeslots. The single relay node (1 ) relays the transmission over several carriers distributed over several timeslots. The latency for this transmission is rather high because six timeslots are needed to transmit the information via several carriers. This relay scheme is for moderate latency requirements with only very few relay nodes but many carriers. The right-hand part of Fig. 6 depicts a relay scheme with few carriers and few relay or coop, nodes. The original transmission is executed on carrier f4. Two retransmissions on carriers f3 and fn-2 are executed in the subsequent timeslots. In parallel, two relay nodes re-transmit the information on the used carriers f3, f4 and fn-2. Three timeslots are used for the whole transmission scenario which results in a relay scheme for latency critical transmissions. Furthermore, during transmission scheme setup, Minimum Sub-band Separation (MSS) shall be used as a parameter that can be set at the central management node. A sub-band is a frequency unit that can be scheduled to any node in the cell for communication. Two sub-bands are then handled as uncorrelated, if they are separated more than the MSS in frequency. It is imaginable that this value for example can be taken from measurements with dedicated hardware and applied to all the deployments with similar characteristics as in the measurement. For instance, consider an OFDMA system. Assume the central management node has three sub-bands of 5MHz bandwidth for scheduling. And further assume a MSS of 2MHz. A single carrier for transmission has a 180kHz bandwidth. In total we get maximal 3 uncorrelated carriers per sub-band of 5MHz and then in total maximal 9 uncorrelated carriers over all sub-bands.

As for frequency diversity a parameter Minimum Transmit-Time Separation (MTS) for the central management node could be used that determines in a similar manner, when it can be assumed that two transmissions over the same channel with same frequency are uncorrelated. It must further be checked how many nodes are needed to guarantee reliability. The probability of packet loss depends on the coding and modulation techniques that are applied at physical layer. With a given physical layer setup a threshold Signal-to-Noise Ratio (SNR) value can be defined that is needed to decode a packet successfully. When a fading margin that fits to the industrial environment is further assumed which is then added to the threshold SNR a target- SNR for that specific system can be determined. If a possible interference should be taken into account an interference margin can be added further and to get a target-SINR. The difference between the target-SNR and the large-scale measurement of the direct link in bootstrapping can be calculated to determine a theoretical diversity order "d" that is needed to grant a demanded level of reliability. The diversity order "d" can be used to create the relay scheme by picking a number of relay nodes and resources. It can be therefore assumed that "d" equals the number of independent copies of the same packet, which is true when it can be ensured that any transmission (direct and relayed) which is applied is uncorrelated to any other by using the three diversity dimensions.

A basic analytical model could be used to determine a value "d" in the way described above, but as long as only a limited number of nodes and resources is available the value of "d" can be assumed to be restricted to below 10. Compared to the requirements in reliability, latency is an easy to handle requirement. The maximum allowed latency given by the application that runs the critical link determines the time diversity which can be used as it is shown in Fig. 6.

An example decision-algorithm for the selection of nodes and resources is located in the block "Choose nodes and schedule resources" from Fig. 7. As an example, assume a required packet loss rate of 10^"9 and a transmission with a maximum of 1 ms latency. The time slot duration is 0.2ms. We set the maximum time diversity to 5 to achieve a latency limit of 5 x 0.2ms = 1 ms. By bootstrapping we find for example a total number of 3 relay nodes that can be used for relaying, because their large-scale SNR is above a certain threshold and they are not correlated to the direct link. From the large-scale SNR of the direct link we calculate a value of "d" = 5.

There could be several degrees of freedom:

time diversity from 1 - 5 (whereas 1 means a non-cooperative transmission, because that would be a single direct transmission) if the MTS is smaller than 0.2ms, spatial diversity from 1 - 3 (whereas 1 means a non-cooperative transmission), · an arbitrary frequency diversity.

In this case for example a mixture of using two nodes with both doing two re-transmissions over uncorrelated channels (which adds 4 to "d") and one re-transmission at the original receiver over an uncorrelated channel than the initial (which adds 1 to "d") is a possible solution. Furthermore, spatial diversity is superior to the other two because this is the only diversity technique that can also help the temporary blocking of the line of sight that usually leads to a deep fade of a longer duration for all frequencies. Adaptation and reconfiguration of the transmission scheme is also contemplated. For instance, at run-time the relaying scheme can be adapted to changes in the cell (removing/ adding of a node; changing large-scale link characteristics, changes in traffic characteristics). Nodes that are not used for the relaying scheme and nodes that are added to the cell can always be tested during run-time, whether they are possible relay nodes for a critical link by the central management node by evaluating their link large-scale characteristics without stopping the actual communication on the critical link. Therefore, we add transmissions for segment 1 and 2 at idle times of RX and TX and collect the channel state information from the receivers like illustrated in Figures 4a and 4b for initial bootstrapping. In addition, if adaptation results in a removed node, such nodes have to be replaced; therefore, the central management node shall also keep and have an updated list in mind with backup-nodes that can be used instead. In general, a removing of nodes is unlikely to happen often in an industrial deployment, but it can be possible that the large-scale characteristics of a link change due to a shadowing of longer duration. In an additional aspect, a HARQ-less scheme for the system 100 is contemplated. In LTE the reliability is ensured by using the HARQ mechanism. HARQ means in FDD-LTE re-transmitting erroneous messages eight time-slots after the initial approach. This is not suitable for latency critical applications. As an initial setup a cooperative concept may be used instead in parallel to HARQ for critical links and switch to HARQ for non-critical links. The decision can be made upon the allowed latency in a hard decision based on a threshold value. Fig. 8 and 9 provide exemplary illustrations of the use of such a cooperative concept.

Fig. 8 depicts a layered architecture with a possible implementation of the cooperative scheduling into existing multi-carrier protocol stack data plane. New and modified blocks are marked with *. A parallel process is introduced into the MAC layer to split-up the MAC layer into a URLLC-part (critical) and a "Relaxed"-part (non-critical). A cooperative scheduling is used for the critical part, wherein a HARQ mechanism is used for non-critical or relaxed links. This implementation is possible for any kind of node (receiver, transmitter, relay nodes). The PHY buffer is only used at relay nodes and the MAC buffer is used at the original transmitter and receiver. The coordination of the relaying is restricted to the central management node.

Fig. 9 shows a possible implementation of the cooperative concept next to the HARQ scheme. Based on the maximum allowed latency (e.g. Ultra-Low (UL) or Low (L)) and the reliability (e.g. Ultrahigh (UH) or Medium (M)) which is indicated in the first two columns a scheme is selected, whereby "Single-Shot Transmission" is a transmission over the direct link without any retransmission. The rows are in the order of increased relay-depth which is the duration of the relay scheme in time, equals time diversity.

The success of the techniques herein can depend on several conditions, such as:

Number of available possible relay nodes in the cell,

Amount of available spectrum (single or multi-band),

Constellation of the nodes inside of the cell.

These factors decide the degree of benefits achieved through the approach. In some cases, a relaying scheme might not be found and therefore the concept cannot be used without adding more spectrum or further possible relay nodes; the system implementing the protocol will detect these cases on its own. Ultimately, a high-level summary of the device- and resource- cooperative approach is the central coordination and configuration of relay schemes for a longtime usage.

The usage of more advanced relaying schemes (for example applying space-time coding or space-frequency coding) than simple amplify-and-forward could be possible by using the same central control and configuration approach.

In sum, the aspects of embodiments described herein seek to exploit spatial, frequency and time diversity in combination to optimize reliability and reduce latency. Reliability becomes scalable by choosing the number of uncorrelated branches to transmit a packet. Additionally, the centrally controlled relaying scheme adds determinism; spontaneous relaying cannot grant reliability of near zero transmit errors and requires additional management procedures that may add a lot of system complexity. In addition, the cooperative approach described herein can be relatively easy to integrate into existing protocol stacks and reuses most of the existing central radio control mechanisms. Turning to Fig. 10, the flow chart illustrates an example method 1000 performed by a central management node 102 described above. For instance, at block 1002, the method may include obtaining reliability and/or latency requirements for a communication that is to be transmitted in a wireless communication system. In addition, at block 1004, the method may include selecting, based on the obtained reliability and/or latency requirements, a transmission scheme for the communication from a set of possible transmission schemes, wherein each of the set of possible transmission schemes is defined by a unique combination of one or more relay nodes, one or more frequencies, and one or more times to be utilized for redundant transmission of the communication in the system. Also, at block 1006, the method may include providing the selected transmission scheme to devices in the system such that the communication is transmitted according to the selected transmission scheme. Further aspects not explicitly shown in Fig. 10 may also be realized by the central management node 102 in further embodiments, including those that include the following features. For example, in method 1000, the central management node can obtain channel quality information associated with one or more communication channels in the wireless communication system. In some examples, selecting the transmission scheme comprises selecting the transmission scheme further on the channel quality information. In addition, the method may include performing a bootstrapping operation that comprises one or more of the obtaining the reliability and/or latency requirements for the communication, obtaining channel quality information associated with one or more communication channels in the wireless communication system, and/or calculating correlation between multiple channels or frequencies. In addition, method 1000 may include providing the selected transmission scheme to devices in the system by transmitting control messages to one or more system devices, where the control information comprises the transmission scheme. According to one aspect, the reliability and/or latency requirements comprise a QoS class associated with the communication. Also, the system may be an industrial automation or manufacturing system or environment in some examples. Without any limitation, the direction for transmission of communications by the devices/nodes described herein can be adapted or selected accordingly when the techniques described herein are used for systems capable of carrying out directional communication. That said, the transmission scheme could benefit from spatial multiplexing in a flexible manner while carrying out relayed transmissions. For instance, the information relaying the selected transmission scheme may also include the direction of transmission and/or direction of reception. The spatial multiplexing aspects may allow to have simultaneous relayed transmissions in time and frequency but in non-interfering directions as an example.

Fig. 11 illustrates an example method 1 100 performed by a relay device 106 in wireless communication network. In some examples, the relay device can obtain channel quality information for at least one channel utilized by the relay device. The example method may also include, at block 1104, transmitting the channel quality information to a central management node of the wireless communication network. In addition, at block 1108, method 1100 includes receiving, from the central management node, a transmission scheme for receiving and/or transmitting a communication to one or more other devices of the system, wherein the transmission scheme is selected by the central management node based on one or more of the channel quality information and/or reliability and/or latency requirements associated with the communication, and wherein the transmission scheme is selected from a set of possible transmission schemes, wherein each of the set of possible transmission schemes is defined by a unique combination of one or more relay nodes, one or more frequencies, and one or more times to be utilized for redundant transmission of the communication in the system. Method 1100 can also include transmitting and/or receiving the communication according to the received transmission scheme. Fig. 12A illustrates additional details of an example central management node 102 of a wireless communication system according to one or more embodiments. The central management node 102 is configured, e.g., via functional means or units (also may be referred to as modules or components herein), to implement processing to perform certain aspects described above in reference to at least Fig. 1 - 3. The central management node 102 in some embodiments for example includes means or units 1230-1250 for performing aspects of method 1000. In at least some embodiments, the central management node 102 comprises one or more processing circuits 1200 configured to implement processing of the method 1000 of Figure 10 and certain associated processing of the features described in relation to other figures, such as by implementing functional means or units above. In one embodiment, for example, the processing circuit(s) 1200 implements functional means or units as respective circuits. The circuits in this regard may comprise circuits dedicated to performing certain functional processing and/or one or more microprocessors in conjunction with memory 1220. In embodiments that employ memory 1220, which may comprise one or several types of memory such as read-only memory (ROM), random-access memory, cache memory, flash memory devices, optical storage devices, etc., the memory 1220 stores program code that, when executed by the one or more for carrying out one or more microprocessors, carries out the techniques described herein. In one or more embodiments, the central management node 102 also comprises one or more communication interfaces 1210. The one or more communication interfaces 1210 include various components (e.g., antennas) for sending and receiving data and control signals. More particularly, the interface(s) 1210 include a transmitter that is configured to use known signal processing techniques, typically according to one or more standards, and is configured to condition a signal for transmission (e.g., over the air via one or more antennas). Similarly, the interface(s) include a receiver that is configured to convert signals received (e.g., via the antenna(s)) into digital samples for processing by the one or more processing circuits. In an aspect, the obtaining module or unit 1230 may comprise or may be in communication with the transmitter and/or receiver. The transmitter and/or receiver may also include one or more antennas. Fig. 13A illustrates additional details of an example relay device 106 according to one or more embodiments. The relay device 106 is configured, e.g., via functional means or units (also may be referred to as modules or components herein), to implement processing to perform certain aspects described above in reference to Fig. 1 - 9 and 1 1. These and potentially other functional means or units (not shown) together perform the features described in the previous figures. In at least some embodiments, the relay device 106 comprises one or more processing circuits 1300 configured to implement processing of the method 1100 of Figure 11 and certain associated processing of the features described in relation to relay device 106, such as by implementing functional means or units above. In one embodiment, for example, the processing circuit(s) 1300 implements functional means or units as respective circuits. The circuits in this regard may comprise circuits dedicated to performing certain functional processing and/or one or more microprocessors in conjunction with memory 1320. In embodiments that employ memory 1320, which may comprise one or several types of memory such as read-only memory (ROM), random-access memory, cache memory, flash memory devices, optical storage devices, etc., the memory 1320 stores program code that, when executed by the one or more for carrying out one or more microprocessors, carries out the techniques described herein. In one or more embodiments, the relay device 106 also comprises one or more communication interfaces 1310. The one or more communication interfaces 1310 include various components (e.g., antennas) for sending and receiving data and control signals. Those skilled in the art will also appreciate that embodiments herein further include corresponding computer programs. A computer program comprises instructions which, when executed on at least one processor of the central management node 102, central management node 106, or relay device 106 cause these devices to carry out any of the respective processing described above. Furthermore, the processing or functionality of central management node 102 or central management node 106 may be considered as being performed by a single instance or device or may be divided across a plurality of instances of central management node 102 or central management node 106 that may be present in a given PLMN such that together the device instances perform all disclosed functionality. In addition, network nodes 106 and/or 108 may be any known type of device associated with a PLMN that is known to perform a given disclosed process or function. Examples of such network nodes include eNBs, Mobility Management Entities (MMEs), gateways, servers, and the like. Embodiments further include a carrier containing such a computer program. This carrier may comprise one of an electronic signal, optical signal, radio signal, or computer readable storage medium. A computer program in this regard may comprise one or more code modules corresponding to the means or units described above.

The present embodiments may, of course, be carried out in other ways than those specifically set forth herein without departing from essential characteristics of the invention. The present embodiments are to be considered in all respects as illustrative and not restrictive, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein. Abbreviations

ARQ Automatic Repeat Request

BS Base Station

C-MTC Critical Machine Type Communication

CRC Cyclic Redundancy Check

D2D Device to Device

HARQ Hybrid ARQ

MAC Medium Access Control

PDCP Protocol Data Convergence Protocol

RLC Radio Link Control PDU Packet Data Unit

TTI Transmission Time Interval

PLC Programmable Logic Controller

QoS Quality of Service

Dev Device

Claims

1. A method of wireless communication performed by a central management node (102) in a wireless communication system, comprising:

- obtaining reliability and/or latency requirements for a communication that is to be transmitted in the wireless communication system;

- selecting, based on the obtained reliability and/or latency requirements, a transmission scheme for the communication from a set of possible transmission schemes, wherein each of the set of possible transmission schemes is defined by a unique combination of one or more relay nodes (106), one or more frequencies, and one or more times to be utilized for redundant transmission of the communication in the system; and

- providing the selected transmission scheme to devices (104; 106; 108) in the system such that the communication is transmitted according to the selected transmission scheme.

2. The method of claim 1 , further comprising obtaining channel quality information associated with one or more communication channels in the wireless communication system, and wherein selecting the transmission scheme comprises selecting the transmission scheme further on the channel quality information.

3. The method of claim 1 or 2, further comprising performing a bootstrapping operation that comprises one or more of the steps of:

- obtaining the reliability and/or latency requirements for the communication;

- obtaining channel quality information associated with one or more communication channels in the wireless communication system;

- calculating correlation between multiple channels or frequencies; and/or

- implementing use of one or more assessment algorithms for performing channel quality estimates.

4. The method of any of the previous claims, wherein providing the selected transmission scheme to devices (104; 106; 108) in the system further comprises transmitting control messages to one or more system devices (104; 106; 108), the control information comprising the transmission scheme.

5. The method of any of the previous claims, wherein the reliability and/or latency requirements comprise a Quality of Service (QoS) class associated with the communication.

6. The method of any or the previous claims, wherein the system comprises an industrial automation or manufacturing system or environment.

7. The method of any of the previous claims, wherein the selected transmission scheme defines one or more of:

for every relay node (106):

which time-frequency resources it is to listen on; and

which time-frequency resources are used for relaying

for a destination device (108), on which time-frequency resources it can expect the transmission and any re-transmissions and relayed transmissions, and for the source device (104), resources for initial transmissions and its own re- transmissions.

8. A central management node (102) in a wireless communication network, the central management node (102) comprising at least a processor (1200) and a memory (1220), the memory (1220) containing instructions executable by the processor (1200) to perform the method of any of claims 1-7.

9. A computer program comprising instructions which, when executed by at least one processor (1200) of a central management node (102), causes it to perform the method of any of claims 1-7.

10. A carrier containing the computer program of claim 9, wherein the carrier is one of an electric signal, optical signal, radio signal, or computer readable storage medium.

11. A method performed by a relay device (106) in wireless communication network, comprising:

obtaining channel quality information for at least one channel utilized by the relay device;

transmitting the channel quality information to a central management node (102) of the wireless communication network; receiving, from the central management node (102), a transmission scheme for receiving and/or transmitting a communication to one or more other devices of the system,

wherein the transmission scheme is selected by the central management node (102) based on one or more of the channel quality information and/or reliability and/or latency requirements associated with the communication, and

wherein the transmission scheme is selected from a set of possible transmission schemes, wherein each of the set of possible transmission schemes is defined by a unique combination of one or more relay nodes (106), one or more frequencies, and one or more times to be utilized for redundant transmission of the communication in the system; and

transmitting and/or receiving the communication according to the received transmission scheme.

12. A relay device (106) in a wireless communication network, the relay device (106) comprising at least a processor (1300) and a memory (1320), the memory (1320) containing instructions executable by the processor (1300) to perform the method according to claim 11.

13. A computer program comprising instructions which, when executed by at least one processor of a relay device, causes it to perform the method of claim 11.

14. A carrier containing the computer program of claim 13, wherein the carrier is one of an electric signal, optical signal, radio signal, or computer readable storage medium.

15. The method of any of claims 1-7, wherein the selection is based on one or more of: an analysis of available system resources, including time, frequency and/or available relay devices for spatial diversity;

a topology of the system and/or associated network(s);

channel conditions in the system; and/or

system device capabilities.