Technical Field

The present disclosure generally relates to a technique for radio access. More specifically, and without limitation, methods and devices are disclosed for requesting and provided access to a radio access network.

Background

The evolution of wireless technologies has changed the way humans communicate and interact with their environment. Next generations of radio access networks, e.g., the fifth generation or 5G according to the Next Generation Mobile Networks (NGMN) Alliance, is expected to also connect nodes communicating without human intervention. The functionality of such nodes may range from minuscule sensors to industrial machines and autonomous vehicles.

Therefore, radio communication has to support a broad range of applications. The radio communication has to support a varying number and density of nodes, different radio communication (or "traffic") patterns of the nodes and different Quality of Service (QoS) requirements of the nodes.

With the nodes changing their traffic behavior over time and significantly different traffic patterns of neighboring nodes, existing schemes for radio resource

management become inefficient. For example, radio time is wasted for sporadic and time-critical traffic in schedule-based radio access networks that have to

overprovision radio resources for unpredictable traffic such as alert messages.

Schedule-based radio access networks have to pre-allocate radio resources according to network size and network topology, whereas inactive nodes or mobile nodes cause changes in the network size and the network topology, which in turn induces a significant control signaling overhead. Moreover, the pre-allocation of radio resources is not efficient with varying traffic characteristics. The fixed allocation of resources does not suit to the varying traffic conditions or patterns. Furthermore, schedule- based radio access networks require additional signaling resources for time synchronization, e.g., cell synchronization. Other existing techniques for radio resource management often fail to fulfill the different communication requirements of such nodes. For example, contention-based radio access, such as Wi-Fi (based on IEEE 802.11) or ZigBee (based on IEEE 802.15.4), may be better suited for dynamic traffic patterns and variations in network size than schedule-based radio access. However, contention-based radio access cannot ensure traffic reliability, especially with increasing traffic load or congestion in the network. Under (e.g., relatively high) traffic load conditions when many contending nodes attempt to access the medium, the number of packet collisions rises. Contention-based access, therefore, typically includes back-off algorithms to reduce the number of packet collisions at the cost of increasing latency for queued packets waiting to be transmitted, contrary to certain communication requirements. Contention-based schemes typically exhibit less channel capacity utilization, especially in congested networks, compared to schedule-based systems. On the other hand, schedule-based access can lead to resource wastage in low traffic conditions or when the allocated resources are not fully utilized.

Summary

Accordingly, there is a need for a radio access technique that supports varying traffic with diverse communication requirements.

As to one aspect, a method of providing access to a radio access network is provided. The method comprises or triggers a step of receiving a plurality of access requests from a plurality of nodes at an access point, each access request specifying one of the nodes and one or more access parameters for data to be exchanged; a step of broadcasting a broadcast message indicative of one or more radio resources assigned to the nodes based on the access requests; and a step of exchanging the data using the one or more assigned radio resources.

At least some embodiments of the technique use a given radio channel capacity efficiently by assigning the radio resources in time and frequency for the data exchange to fulfill varying traffic demands of the nodes according to the access requests and/or in fulfillment of diverse node-specific communication requirements according to the access parameters. While in schedule-based access allocated resources can be wasted (e.g., if not used by the owner of the resources), the technique can be implemented so that unused resources are available to other nodes. The access point may also be referred to as a base station. The access point may be stationary. The nodes may also be referred to as stations or terminals. At least one or each of the nodes may be mobile or portable. The nodes may include

autonomously operating nodes, user equipments or a combination thereof.

Each of the access requests may specify a communication demand (or "traffic" demand) of the corresponding node from which the access request is received. At least one or each of the access requests may be included in a radio frame. The radio frame may also be referred to as a traffic indication frame.

At least one or each of the access parameters may specify one or more

communication requirements (or "traffic" requirements) of the corresponding node from which the access request specifying the access parameter is received. Different access parameters may be received from different nodes. For example, assigning the time slots specifically for each node according to its access request and/or all received requests can resource-efficiently fulfill the communication requirements. Alternatively or in addition, the access parameters received from at least one or each of the nodes may vary over time. The access parameters may represent variable communication requirements. For example, radio resources can be dynamically used by assigning the time slots based on the currently or most recently received access parameters. The technique may implement an adaptive radio resource allocation.

The plurality of access requests may indicate a network size, a network topology or a change of the network size or the network topology. The time slots may be assigned dynamically according to varying communication demands, a varying network size and/or a varying network topology, e.g., as indicated by the access parameters or access requests. The technique may implement a dynamic medium access.

The data exchange may include Machine Type Communication (MTC) or Machine-to- Machine (M2M) communication. At least one or each of the nodes may communicate without human intervention. At least one or each of the access requests may be triggered without human intervention. The nodes may be controlled or serviced through the radio access network. The nodes may be controlled or serviced without local user interaction at the nodes and/or without user interfaces at the nodes. The access requests may be triggered by machine events. The plurality of nodes may include at least one of sensors, actuators, home appliances, (e.g., autonomous) vehicles and industrial manufacturing equipment. The data exchange (or the access requests thereto) may be periodic, e.g., in relation to a certain node. E.g., the exchanged data may include monitoring messages or status update messages. Alternatively or in addition, the data may be exchanged occasionally, e.g., on-demand or event-driven. The periodic or occasional data exchanges may include large data volumes, e.g., data exchanges beyond the 90th percentile in terms of the amount of the data exchanged based on one access request. The large data volumes may include reports, log files, memory dumps and updates of software (e.g., firmware) of the corresponding node. Alternatively or in addition, the data exchange may include an unpredictable or sporadic exchange of data that is time-critical, such as control messages, command messages, emergency or alert messages, etc.

Each of the radio resources may be defined by one or more different time slots, one or more different frequency channels, one or more different antennas and/or a combination or sub-combination thereof. Alternatively or in addition, the different radio resources may relate to different spatial layers (or streams).

The data may be exchanged during the one or more assigned time slots and/or on the one or more assigned frequency channels, optionally using the one or more assigned antennas. The method for providing access and/or the one or more assigned antennas may be implemented exclusively at the access point. The antennas may be spaced apart. One or more of the steps may be implemented using spatial diversity by means of the assigned antennas. Alternatively or in addition, two or more assigned antennas may implement pattern diversity, polarization diversity and/or adaptive antenna arrays.

The broadcast message may be indicative of a first set of different radio resources among the radio resources. The radio resources may be assigned to a first node of the nodes, optionally for redundantly exchanging first data. For example, redundancy may be triggered to ensure higher reliability, e.g., if the access parameters are indicative of high-priority data and/or QoS parameters indicating high reliability demands.

Redundant radio resources may be avoided for transmissions to and/or from the access point owing to the higher reliability ensured by a multi-antenna system at the access point. Node-to-node transmission, however, typically does not have multi- antenna system. For at least one or each of the nodes, the broadcast message may be indicative of a set of one or more radio resources. The set may be node-specific in that the broadcast message may be indicative of different sets for different nodes. Optionally, the broadcast message is indicative of a set of one or more different radio resources for each of the nodes.

The radio resources in each set may be assigned to the corresponding one of the nodes, e.g., for redundant data exchange. Redundant data exchange may

encompass that the same first data is exchanged using each of the different radio resources of a first set assigned to a first node. The first data may be a part of the data that is exchanged in the radio access network. In some embodiments, the redundancy of the radio resources is not always ensured. For example, the access point may decide upon redundancy by trading-off resource utilization for improving reliability.

The first set may include (as a first radio resource) a first frequency channel in combination with a first time slot assigned to the first node and (as a second radio resource) a second frequency channel in combination with a second time slot assigned to the first node.

By assigning multiple time slots spread over different frequency channels, the technique can be implemented to support variable traffic while satisfying traffic QoS demands as to both latency and reliability, e.g., according to the access parameters.

The technique can implement a hybrid approach for medium access in the receiving step with contention-based access and schedule-based access principles in the broadcasting step and the exchanging step, e.g., to address the needs of a wide range of Machine Type Communication (MTC) or Machine-to-Machine (M2M) communication applications. Furthermore, the technique can be implemented for MTC applications, especially in the area of wireless industrial automation (WIA), where it is often impractical to achieve high reliability by means of advanced multi- antenna radio interface for device-to-device (D2D) communication (e.g., as compared to a radio link between the node and the access point using a high-gain antenna and/or beamforming).

The data to be exchanged can include real-time traffic, e.g., small-sized data (which may be exchanged periodically as well as aperiodically). The real-time traffic may require in the access parameters both high degree of reliability and low-latency communication. Since different types of traffic patterns often coexist in the radio access network, the hybrid approach can be implemented to meet the required reliability for time-critical traffic within the timeliness requirements (e.g., for latency).

The first frequency channel may be different from the second frequency channel. The first frequency channel may occupy a first radio frequency spectrum that is disjoint from a second radio frequency spectrum occupied by the second radio frequency channel. Furthermore, the disjoint frequency channels may belong to a common radio spectrum. As an example, in the 5 GHz band, a first frequency channel may be centered at 5.18 GHz and a second frequency channel may be centered at 5.24 GHz, wherein each frequency channel has 10 MHz of bandwidth.

The first time slot assigned to the first node may be before the second time slot assigned to the first node. For at least one or each of the nodes, the first time slot and the second time slot may be disjoint. The first time slot and the second time slot may be at least one of temporally shifted, non-overlapping and temporally separated.

Some or each of the nodes (e.g. nodes implementing MTC or M2M communication) may include a half-duplex radio. The radio may (e.g., primarily) use a certain fixed bandwidth (i.e., frequency channel) at a given time. The additional (e.g., redundant) radio resources (on different frequency channels) are assigned in temporally non- overlapping time slots. Alternatively or in addition, the radio resource assignment increases the bandwidth and/or the number of frequency channels assigned for a given time so that the radio resources are temporally overlapping (i.e., more than one radio resource is assigned at a given time) for increasing reliability of the data exchange.

The broadcast message may be indicative of a second set of different radio resources that are assigned to a second node of the nodes, e.g., for redundantly exchanging second data. The radio resources of the first set and/or the second set may use the same frequency channel used by the access point for the broadcast message. The first set and the second set may be disjoint. The same second data may be exchanged using each of the different radio resources of the second set.

The second set may include (as a first radio resource) the second frequency channel in combination with a first time slot assigned to the second node and (as a second radio resource) the first frequency channel in combination with a second time slot assigned to the second node. The first time slot assigned to the second node may be before the second time slot assigned to the second node.

The first time slot assigned to the second node may be before the second time slot assigned to the first node. Alternatively or in addition, the first time slot assigned to the first node may be before the second time slot assigned to the second node.

A number of the radio resources in the first set may depend on the access request or a class indicator received from the first node. Optionally, the number of the radio resources in the first set further depends on the access parameters or class indicators received from the other nodes and/or previous access requests that are currently pending (e.g., access requests of earlier cycles that have not yet led to a radio resource assignment).

The plurality of access requests may be received in a first phase. Alternatively or in addition, the broadcast message may be broadcasted in a second phase.

Alternatively or in addition, the data may be exchanged in a third phase. The first phase may be different from (e.g., non-overlapping with) the second phase. The second phase may be different from (e.g., non-overlapping with) the third phase. The third phase may be different from (e.g., non-overlapping with) the first phase.

The access requests may be received (e.g., received at the access point and/or sent by the nodes) according to a contention scheme. Any node (e.g., any node associated with the radio access network or a node newly accessing the radio access network) may be allowed to send its access request at any time (e.g., according to a first come - first served - scheme) within the first phase. Even within the first phase, subsets of nodes may be assigned time slots for contention-based access.

The broadcast message (e.g., the broadcast message of a previous cycle) may include a command that allows the nodes to send the access requests in the first phase. The broadcast message (e.g., the broadcast message of a previous cycle) may specify the first phase (e.g., the first phase of a current cycle).

The technique may combine contention-based access requests (e.g., in the first phase) with schedule-based data exchange (e.g., in the third phase). The data exchange may be scheduled in the second phase and/or by means of the broadcast message. The data exchange in the third phase may be scheduled (e.g., by determining the time slots) based on the access requests in the first phase. The access point may determine the time slots, e.g., autonomously and/or based on the access parameters. The technique can be implemented in a centrally controlled radio access network, e.g., at the access point. Alternatively or in addition, the radio access network may include a plurality of the access points. Each of the access points may implement the technique, e.g., at a certain level of granularity in terms of coverage area and/or number of nodes. The plurality of access points, e.g., access points within range of mutual radio communication, may define disjoint (e.g., non- overlapping and/or consecutive) first phases for the reception of access requests at the respective one of the access points.

The first phase may be divided into (e.g., disjoint) contention intervals (also referred to as sub-phases or contention time slots). The contention intervals may be allocated to groups (e.g., disjoint subsets) of the nodes for receiving the access request according to the contention scheme within the assigned contention time slot. This allocating or grouping of nodes for contention-based access may also be referred to as group contention. The group contention may be triggered or performed, when the number or the density of the nodes increases beyond a certain (e.g., configurable) threshold value. The group contention may be triggered by a number of nodes associated to the access point. The access point (e.g., the only access point in the access network, or at least one or each of the access points) may trigger or perform the group contention.

For group contention, the access point may allocate a certain contention interval to a group (e.g., a proper subset) of the nodes, e.g., by means of the broadcast message (e.g., the broadcast message of a previous cycle). The broadcast message (e.g., the broadcast message of a previous cycle) may be indicative of the nodes belonging to the group and/or the contention interval allocated to the group. The group contention may allow reducing a number of potential contenders at a given point of time and/or throughout the contention interval. The number of nodes sending access requests or allowed sending access requests in the second phase may be unchanged. Within the allocated contention interval, the access requests may be sent (e.g., exclusively) by the nodes belonging to the corresponding group, e.g., without coordination among the nodes belonging to the group. For example, the group contention can reduce a collision rate of the access requests. By virtue of the group contention or in combination with the group contention, resource-efficient and low- latency radio access may be supported. At least one or each of the nodes may be allowed to reduce power consumption, e.g., by restricting radio operation and/or turning off an antenna amplifier at least in the third phase during time slots not assigned to the corresponding node. Any node that is not involved in a communication (i.e., not a transmitter or a receiver, e.g., not sending or receiving data and/or not requesting access) in a particular time slot may reduce its power consumption. The at least one node, at least another node or each node may be required to restore the radio operation and/or turn on the antenna amplifier prior to the second phase.

Exchanging the data, as used herein, may encompass a unidirectional or a bidirectional radio communication. The step of exchanging the data may be implemented by sending the data and/or receiving the data. Sending the data may include at least one of unicast transmission, multicast transmission and broadcast transmission.

Alternatively or in addition, the data may be exchanged between at least two of the access point and the nodes. Exchanging the data, as used herein, may encompass any radio communication, e.g., involving at least one of the nodes. The exchange of data may be implemented by sending the data from the access point to the at least one of the nodes (which may also be referred to as downlink communication).

Alternatively or in addition, the exchange of data may be implemented by receiving the data at the access point from the at least one of the nodes (which may also be referred to as uplink communication). Alternatively or in addition, the exchange of data may be implemented by exchanging the data between two or more of the nodes.

The access equipment and/or the access point may or may not be involved in the data exchange. In one example case, at least one transmission and at least one reception is requested (and, e.g., needed) for the data exchange. For instance, the data exchange occurs between two nodes without involving the access point (at least as a receiver or transmitter), e.g., under the control of the access point. For at least one transmitting node or at least one receiving node, the data exchange may involve the access point, e.g., as a receiver or as a transmitter, respectively.

The access parameters may include at least one of a source address for the data (or two or more source addresses), a destination address for the data (or two or more destination addresses), an amount of the data and a class indicator for the data. The class indicator may be indicative of a traffic class or access category. The class indicator may specify at least one of a Quality of Service (QoS) for the data and a priority for the data. Alternatively or in addition, the QoS may define the priority, or vice versa. The class indicator may be defined similarly to, or compatible with, the standard IEEE 802. lie. Alternatively or in addition, a specific priority classes may be defined (e.g., depending upon the application exchanging the data). The specific priority classes may indicate data from a sensor, actuator, controller, gateway, etc.

The second phase and/or the broadcast message may include a timing

synchronization signal or may imply a timing synchronization for time-synchronizing the nodes with the access point. The technique may be implemented to allow the nodes to implicitly time-synchronize with the access point, e.g., without requiring an additional or explicit control message and/or without highly accurate oscillators at the nodes.

The first phase, the contention intervals in the first phase, the third phase and/or the time slots in the third phase may be defined relative to the second phase (e.g., of a current cycle) and/or the broadcast message (e.g., of a current cycle). The broadcast message may indicate at least one of the first phase, the contention intervals in the first phase, the third phase and/or the time slots in the third phase according to the relative definition.

The second phase and/or the broadcast message may define a beginning of a cycle for the radio access. The cycle may include the second phase, the first phase and the third phase in sequence. The cycle may be periodically and/or continuously repeated. At least two of the second phase, the first phase and the third phase may be consecutive.

A duration of the cycle (cycle duration) may be variable. Alternatively or in addition, the cycle duration may be determined independently for each cycle. The cycle duration may be different for at least two subsequent cycles. The cycle duration of one cycle may be independent of the cycle duration of another cycle, e.g., the previous cycle. For example, the cycle duration (e.g., for the next cycle) may depend on a number and/or a duration of the time slots requested (e.g., in the cycle prior to the next cycle) by the nodes.

In one of the cases, the access point may completely skip assigning a time slot (or may assign only a limited or partial duration time slot) to a particular node, for instance due to the fact that this node has relatively low priority (e.g., non-urgent) traffic and other nodes have relatively high priority traffic. Unless new traffic arrives at this node, this node may refrain from contending again for the medium. Thus, unnecessary congestion in the radio access network can be avoided. Based on the previous access request of this node, the access point may assign this node a time slot in one or more future cycles. For example, the time slot assigned to a node may not necessarily be based on the access request received from the node in the previous cycle but in any of the previous cycles.

The broadcast message of the cycle may be based on access requests received in one or more other cycles prior to the cycle. The broadcast message may be based on not yet assigned access requests received up until (and including) the previous cycle. The broadcast message of the cycle may be indicative of time slots within the same cycle.

The one or more time slots assigned to one of the nodes may also depend upon the access requests (e.g., traffic QoS requirements) from the other nodes. Alternatively or in addition, a duration of the one or more time slots assigned to one of the nodes (slot duration) may depend on the access parameters of the one node. The slot duration may further depend on the access parameters of the other nodes.

The access point may determine the slot durations for the nodes collectively, e.g., based on a priority assigned to each of the nodes for which an access request has been received. For instance, if the access request may indicate (e.g., by means of the access parameters) a low priority (e.g., a relatively low priority compared to the other nodes) and a high volume of traffic (e.g., a relatively large amount of the data compared to the other nodes), the access point may split the requested data exchange across two or more cycles. Alternatively, or in addition, if one or more other access requests indicate traffic with high priority for the other nodes, the access point may determine to not assign a time slot (which is also referred to as skipping of the time slot assignment) for the node, the access request of which indicates high-volume and/or low-priority traffic in a particular cycle.

A duration of the access request (request duration) may be less than the slot duration of the one or more time slots assigned based on the access request. The request duration of each of the access requests may be less than the slot duration of the one or more time slots assigned based on the corresponding one of the access requests. The request duration of each of the access requests may be less than the slot duration of each of the time slots. Throughout, "duration" (e.g., for cycle, slot or request) may be defined as a transmission time (e.g., for the cycle, the slot or request, respectively). The transmission time may also be referred to as air time. Alternatively or in addition, the assigned one or more time slots may be used for transmitting multiple frames. In this case, the air time may or may not include an inter-frame gap. The transmission time or slot duration may be the sum of frame transmission times and the one or more inter-frame gaps.

The time slots may be assigned to the nodes only in response to the access requests received from the nodes. The access point may be one of the nodes. E.g., in order to reduce the risk for congestion, the access point itself does not contend during the contention phase. This can further reduce a congestion level (which in turn may also be beneficial for the nodes).

A further node (e.g., another node apart from the associated nodes) may be associated with the access point upon receiving the access request from the further node. At least some embodiments can associate any newly appearing node, e.g., in the vicinity of the access point, based on the access request.

The method may further include determining, e.g., by the access point, the radio resources (e.g., time slots and a frequency channel for each of the time slots) to be assigned to the nodes. The radio resources may be determined based on any criterion described herein (e.g., traffic priority, number of nodes, slot duration, pending requests, traffic QoS demands, etc., and optionally including combinations and sub-combinations thereof)- The radio resources may be prioritized and/or managed. The assignment of the radio resources, e.g., for a cycle, may result from applying one or more of the criteria to the corresponding one of the nodes individually and/or a collective assessment of the access requests (e.g., traffic indications) from different nodes or all of the nodes having sent their access requests. The access point may be configured to assign priorities to the nodes based on their access request parameters.

The assignment of radio resources (e.g., time slots in conjunction with different frequency channels) may also depend on a total number of frequency channels available at a given time, e.g., the next cycle. For instance, the number of available channels in one deployment of the radio access network may be greater than the number of available channels in another radio access network deployment. The available number of frequency channels may also vary during the course of operation of the radio access network. Since the radio resource assignment is carried out dynamically in every cycle, embodiment can flexibly benefit from the available frequency channels at any given time. The number of available frequency channel may directly influence the radio resource assignment. For example, if the number of available frequency channels decreases, the duration of the cycle (that is subject to assignment) may be increased, e.g., to meet a targeted number of assigned radio resources.

As to another aspect, a method of requesting access to a radio access network is provided. The method comprises or triggers a step of sending an access request from a node to an access point, the access request specifying the node and one or more access parameters for data to be exchanged; a step of receiving a broadcast message indicative of one or more radio resources assigned to the node based on the access request; and a step of exchanging the data using the one or more assigned radio resources.

The step of sending the access request may include a carrier sense multiple access. The node may be configured to perform a carrier sensing operation, e.g., based on radio frequency (RF) energy detection. The node may be configured to sense the radio medium and determine whether it is idle or busy. This functionality may be employed for the first phase. The contention in the first phase may employ the carrier sense multiple access with a collision avoidance (CSMA/CA) procedure.

As to a further aspect, a computer program product is provided. The computer program product comprises program code portions for performing any one of the steps of the method aspects disclosed herein when the computer program product is executed by one or more computing devices. The computer program product may be stored on a computer-readable recording medium. The computer program product may also be provided for download via a data network, e.g., the radio access network and/or the Internet.

As to a still further aspect, an access equipment for providing access to a radio access network is provided. The access equipment comprises a reception module for receiving a plurality of access requests from a plurality of nodes at an access point, each access request specifying one of the nodes and one or more access parameters for data to be exchanged; a broadcast module for broadcasting a broadcast message indicative of one or more radio resources assigned to the nodes based on the access requests; and an exchange module for exchanging or triggering exchanging the data using the one or more assigned radio resources.

The access equipment may be identical or collocated with the access point. The access equipment may include the access point. The access equipment or the access point may be coupled to a backhaul network and/or the Internet.

As to a still further aspect, a node equipment for requesting access to a radio access network is provided. The node equipment comprises a send module for sending an access request from a node to an access point, the access request specifying the node and one or more access parameters for data to be exchanged; a reception module for receiving a broadcast message indicative of one or more radio resources assigned to the node based on the access request; and an exchange module for exchanging the data using the one or more assigned radio resources.

The node equipment may be identical or collocated with the node. The node equipment may include the node. The node equipment or the node may be coupled to a sensor. The node equipment or the node may be coupled to an actuator, controller, etc., e.g., in a factory automation application.

As to another aspect, a device for providing access to a radio access network is provided. The device is configured to perform the one method aspect. Alternatively or in addition, the device comprises a receiving unit configured to receive a plurality of access requests from a plurality of nodes at an access point, each access request specifying one of the nodes and one or more access parameters for data to be exchanged; a broadcasting unit configured to broadcast a broadcast message indicative of one or more radio resources assigned to the nodes based on the access requests; and an exchanging unit configured to exchange or trigger exchanging the data using the one or more assigned radio resources.

As to another aspect, a device for requesting access to a radio access network is provided. The device is configured to perform the other method aspect. Alternatively or in addition, the device comprises a sending unit configured to send an access request from a node to an access point, the access request specifying the node and one or more access parameters for data to be exchanged; a receiving unit configured to receive a broadcast message indicative of one or more radio resources assigned to the node based on the access request; and an exchanging unit configured to exchange the data using the one or more assigned radio resources. At least one or each of the access equipment, the node equipment and the devices may further include any feature disclosed in the context of the method aspects.

Particularly, any one of the modules or the units, or a dedicated module or unit, may be configured to perform one or more of the steps of any one of the method aspects.

The access equipment or the access point may be configured to decide on a radio resource assignment (optionally including a time slot assignment), e.g., based on the access request (e.g., traffic QoS requirements or addressing fields) received from the corresponding one of the nodes and/or the access requests (e.g., traffic QoS requirements or addressing fields) received from all of the nodes at a given time, e.g., in a particular cycle.

The access request or the access parameters may also have a limiting effect on the radio resource assignment. For example, if the address fields of the access request are indicative of only two nodes having a need for unicast transmission to each other, the access request does not permit assigning different frequency channels. Alternatively or in addition, if the access request is indicative of a broadcast transmission, simultaneous redundant channels are not assigned.

In at least some embodiments, the access point can flexibly manage and/or prioritize medium access among the nodes.

Moreover, for any step or feature disclosed in the context of the access point, a corresponding feature is optionally disclosed in the context of the node.

Brief Description of the Drawings

Further details of embodiments of the technique are described with reference to the enclosed drawings, wherein:

Fig. 1 shows a schematic block diagram of an access equipment for providing access to a radio access network;

Fig. 2 shows a schematic block diagram of a node equipment for requesting access to a radio access network; shows a flowchart for a method of providing access to a radio access network; shows a flowchart for a method of requesting access to a radio access network; schematically illustrates phases for a radio access cycle for operating the equipments of Figs. 1 or 2 performing the methods of Figs. 3 or 4; schematically illustrates phases for a radio access cycle for operating the equipments of Figs. 1 or 2 performing the methods of Figs. 3 or 4 using different frequency channels; schematically illustrates phases for a radio access cycle for operating the equipments of Figs. 1 or 2 performing the methods of Figs. 3 or 4 using different frequency channels and variable slot lengths; schematically illustrates interleaved phases of cycles according to Fig. 5; schematically illustrates interleaved phases of cycles using different frequency channels according to Fig. 6 or 7; schematically illustrates a unicast transmission pattern involving bidirectional communication in one of the phases of Figs. 5 to 9; schematically illustrates a unicast transmission pattern involving bidirectional communication using different frequency channels in the phases of Figs. 5 to 9; schematically illustrates phases for a radio access cycle for operating the equipments of Figs. 1 or 2 performing the methods of Figs. 3 or 4 with different data priorities; shows a flowchart for an implementation of the method of Fig. 3; shows a flowchart for another implementation of the method of Fig. 3; shows a flowchart for an implementation of the method of Fig. 4; Fig. 16 shows a flowchart for another implementation of the method of Fig. 4;

Fig. 17 shows a schematic block diagram of a device for providing access to a radio access network; and

Fig. 18 shows a schematic block diagram of a device for requesting access to a radio access network.

Detailed Description

In the following description, for purposes of explanation and not limitation, specific details are set forth, such as a specific network environment in order to provide a thorough understanding of the technique disclosed herein. It will be apparent to one skilled in the art that the technique may be practiced in other embodiments that depart from these specific details. Moreover, while the following embodiments are primarily described for a Fifth Generation or Next Generation Mobile Networks (NGMN) implementation, it is readily apparent that the technique described herein may also be implemented in any other wireless communication network compatible with at least one of the Global System for Mobile Communications (GSM), the Universal Mobile Telecommunications System (UMTS), 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), 3GPP LTE-Advanced, a Wireless Local Area Network (WLAN) according to the standard family IEEE 802.11 (e.g., IEEE 802.11a, g, n, ac and/or e), ZigBee according to the underlying standard IEEE 802.15.4 and a Worldwide Interoperability for Microwave Access (WiMAX) according to the standard family IEEE 802.16.

Moreover, those skilled in the art will appreciate that the modules, functions, steps and units explained herein may be implemented using software functioning in conjunction with a programmed microprocessor, an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA), a Digital Signal Processor (DSP) or a general purpose computer, e.g., including an Advanced RISC Machine (ARM). It will also be appreciated that, while the following embodiments are primarily described in context with methods, equipments and devices, the invention may also be embodied in a computer program product as well as in a system comprising a computer processor and memory coupled to the processor, wherein the memory is encoded with one or more programs that may perform the functions, steps and implement the modules and units disclosed herein. Fig. 1 schematically illustrates a block diagram of an access equipment 100 for providing access to a radio access network. The access equipment 100 includes a reception module 102 that receives a plurality of access requests from a plurality of nodes at an access point. Each access request specifies one of the nodes and one or more access parameters for data to be exchanged. A broadcasting module 104 of the access equipment 100 sends a broadcast message indicative of one or more radio resources assigned to the nodes based on the access requests. An exchanging module 106 is involved in exchanging or triggers the exchanging of the data using the one or more assigned radio resources. Optionally, the exchanging module 106 surveys the data exchange.

Fig. 2 schematically illustrates a block diagram of a node equipment 200 for requesting access to a radio access network. The node equipment 200 includes a send module 202 that sends an access request from a node to an access point. The access request specifies the node and one or more access parameters for data to be exchanged. A reception module 204 of the node equipment 200 receives a broadcast message indicative of one or more radio resources assigned to the node based on the access request. An exchange module 206 sends and/or receives the data using the one or more assigned radio resources.

In one embodiment, the send module 202 is configured to sense the radio medium before sending the broadcast message. This may be performed according to a listen- before-talk (LBT) scheme (e.g., CSMA/CA).

Fig. 3 shows a flowchart for a method 300 of providing access to a radio access network. In a step 302 of the method 300, a plurality of access requests is received from a plurality of nodes at an access point. Each access request specifies one of the nodes and one or more access parameters for data to be exchanged. A broadcast message indicative of one or more radio resources assigned to the nodes based on the access requests is broadcasted in a step 304. The data is exchanged using the one or more assigned radio resources in a step 306.

Assigning the one or more radio resources may include assigning one or more time slots. Optionally, each time slot is further associated with a frequency channel.

The method 300 may be performed by the access equipment 100. E.g., the modules 102, 104 and 106 may perform the steps 302, 304 and 306, respectively. The access point may also be referred to as a central coordinator of the radio access network, a controller of the radio access network or a base station of the radio access network.

The steps 302, 304 and 306 may be performed in three different phases of a radio access protocol, respectively. The radio access protocol may define a cycle that is periodically repeated. Each cycle may include the three different phases. The steps 302 to 306, as functionally linked by the method 300, may be performed in different cycles. E.g., the step 302 may be performed in a first cycle and the steps 304 and 306 may be performed in a second cycle after, e.g., subsequent to, the first cycle.

The data exchange as such may or may not involve the access point. The access point may govern the assigning of the radio resource (e.g., the time slot). The nodes may perform unicast or multicast transmissions. A node performing a broadcast transmission may involve the access point as a receiver thereof.

Fig. 4 shows a flowchart for a method 400 of requesting access to a radio access network. In a step 402 of the method 400, an access request is sent from a node to an access point. The access request specifies the node and one or more access parameters for data to be exchanged. A broadcast message indicative of one or more radio resources assigned to the node based on the access request is received in a step 404. The data is exchanged using the one or more assigned radio resources in a step 406.

The one or more radio resources, as indicated by the broadcast message, may define one or more time slots. Optionally, a frequency channel is indicated for each time slot.

The method 400 may be performed by the node equipment 200. E.g., the modules 202, 204 and 206 may perform the steps 402, 404 and 406, respectively. The nodes may be terminals of the radio access network.

The steps 402, 404 and 406 may be performed in the three different phases of the radio access protocol, respectively. The steps 402 to 406, as functionally linked by the method 400, may be performed in different cycles. E.g., the step 402 may be performed in the first cycle and the steps 404 and 406 may be performed in the second cycle after, e.g., subsequent to, the first cycle. The technique may be implemented by combining schedule-based data exchange in the steps 206 and 306 with contention-based radio access in the steps 202 and 302 to support variable traffic patterns in a highly efficient manner. While embodiments of the technique nevertheless address static scenarios efficiently, the technique is applicable to a wide range of Machine Type Communication (MTC) scenarios with dynamic radio communication requirements. The dynamic requirements may include network size variations and/or variable traffic patterns (e.g., different traffic volumes, changing traffic arrival rates or different number of nodes generating traffic).

Different priority levels or variations may also impart an effect on how the radio access is governed by the access point.

Embodiments may adapt and/or reconfigure the schedule-based data exchange in the steps 306 and 406 according to the contention-based radio access requests in the steps 302 and 402 to fulfill the instantaneous traffic demands and/or to provide radio access to a number of active nodes at a given time. The data exchange may thus satisfy the current and node-specific traffic QoS demands with efficient radio resource utilization.

The access equipment 100 may be connected with the access point to control the access point according to the method 300. Alternatively or in addition, the access equipment 100 may be implemented by the access point. For brevity, and without limitation, the access point is referred to using the reference sign 100.

The node equipment 200 may be connected with the node to control the node according to the method 400. Alternatively or in addition, the node equipment 200 may be implemented by the node. For brevity, and without limitation, the node is referred to using the reference sign 200.

In embodiments using multiple frequency channels, the schedule-based access is carried out in a dynamic fashion and can be distributed across multiple available frequency channels. The nodes 200 can indicate individual traffic demands, traffic QoS requirements, and address information (e.g., source and/or destinations) to the access point 100 using contention-based access in a given frequency channel. The schedule-based access is carried out dynamically in multiple available frequency channels based on the overall instantaneous traffic QoS demands in the network (e.g., from all nodes with data traffic), available frequency channels and addressing information. Based on the current traffic characteristics, number of nodes, traffic QoS requirements and the available frequency channel, the access point may dynamically configure the duration of the contention-based and schedule-based access. The access point 100 may manage priority and device-to-device (D2D) data exchange in the schedule-based access to nodes considering the overall traffic characteristics. The method can be applied to an arbitrarily number of frequency channels.

Preferably, the number of access requests by the nodes 200 and their priority levels (i.e., reliability and latency requirements indicated in the access parameters) directly control how many repetition time slots are assigned in different frequency channels.

The access requests, as received by the nodes 200, may indicate the presence of data, the amount of data, the QoS demand, the addressing information, etc.

Preferably, the access requests do not explicitly request or specify the number of radio resources or time slots that are to be assigned by the access point.

An exemplary structure of the radio access network is described. The radio access network includes the access point 100. A network architecture and/or a network topology of the radio access network may be controlled by the access point 100. A variable number of nodes 200 can be associated with the access point.

The radio access is coordinated by the access point 100. The radio access can be distinctly divided into contention-based radio access and schedule-based data exchange. Based on a current traffic characteristics (e.g., the number of access requests), the traffic QoS demands and/or a number of nodes 200, the access point 100 dynamically configures a duration of the contention-based radio access and/or a duration of the schedule-based data exchange.

The nodes 200 indicate, to the access point 100, their individual traffic demands by means of the access requests and their individual traffic characteristics by means of the access parameters using the contention-based radio access.

According to the traffic demands, the access point 100 dynamically assigns the time slots to those nodes 200 that have traffic demands. The assignment information is broadcasted to all the nodes 200 in the vicinity by the access point 100 in the step 304. The broadcast information in the broadcast message also serves to implicitly time-synchronize the radio access network.

Optionally, the assignment of the time slot to the nodes 200 for the schedule-based data exchange takes traffic priority into account. For example, the access point 100 determines the time slots based on the overall traffic characteristics of all nodes 200. The access point 100 adapts the assignment of radio resources according to the instantaneous traffic demands expressed by the access requests and the traffic QoS requirements specified by the access parameters of individual nodes as well as the overall traffic characteristics at a given time.

During the contention-based radio access, the access point 100 allows one or more nodes 200 (that are not yet associated with the access point 100) to join the radio access network and indicate their traffic demand according to the steps 302 and 402. The access point 100 accommodates a variable number of nodes 200 at a given instant of time and dynamically assigns the radio resources. Associating further nodes 200 in this way is useful for a wide range of MTC applications, e.g., including node mobility. Optionally, some nodes 200 (e.g., battery-powered devices) are put to a dormant state to conserve power. Such nodes 200, upon becoming active, listen to the broadcast message to rejoin the network.

In an embodiment, the first phase for contention-based radio access according to the steps 302 and 402 is sub-divided into contention intervals. Only a certain group (i.e., a subset) of the nodes 200 contend with one another at a given time by indicating their instantaneous traffic demands to the access point 100 by means of the access requests. This group contention can ensure a high degree of access reliability, if the radio access network is densely deployed with nodes 200.

In a variant compatible with any aspect and embodiment described above, the time and/or frequency radio resources are dynamically allocated for the contention-based radio access of the first phase (optionally including the group contention) in the steps 302 and 402. Alternatively or in addition, the time and/or frequency radio resources are dynamically assigned for the schedule-based data exchange of the third phase in the steps 306 and 406, e.g., in order to achieve efficient resource utilization and satisfy traffic QoS demands.

Fig. 5 schematically illustrates phases of an exemplarily radio access protocol or medium access procedure 500. The medium access procedure 500 is divided into the three distinct phases defining a cycle 510. Fig. 5 shows a simplistic case for illustrating the phases, while the radio resources are on a single frequency channel.

The first phase 502 includes the access requests according to the steps 302 and 402. The first phase 502 is also referred to as a contention phase. The second phase 504 includes a broadcast transmission according to the steps 304 and 404. The broadcast message may also be referred to as a beacon or a beacon frame. The beacon frame defines the beginning of the cycle 510. In the example illustrated in Fig. 5, three nodes 200 transmit traffic indication frames using the contention-based access after receiving the beacon frame. The third phase 506 includes the schedule-based data exchange.

In another implementation of the medium access procedure 500, the contention phase 502 follows the schedule-based access phase 506 in the cycle 510. In this case, a cycle order constitutes beacon transmission in the second phase 504, schedule-based access in the third phase 506 and the contention phase 502.

In one implementation, the three phases are distinguished exclusively by time. E.g., the data exchange in the third phase 506 may use the same radio frequency resources (e.g., the same carrier frequency and/or the same subcarriers) used for the access requests in the first phase 502. In another implementation, at least two of the three phases are distinguished by means of at least one of code division, radio frequency resources and spatial streams (e.g., using a multiple input multiple output, MIMO, channel).

Alternatively or in addition, the beacon transmission (in the steps 304 and 404), the traffic indication frame transmission (in the steps 302 and 402) and the data exchange (in the steps 306 and 406) are performed using different (e.g., dynamically assigned) time and/or frequency resources. For example, the beacon frame transmission and the transmission of traffic indication frames may be performed on a single dedicated control channel, while the schedule-based access is carried out at multiple time and/or frequency resources, e.g., in a dynamic fashion in each cycle 510.

The three phases are collectively referred to as the cycle 510. The cycle may be periodic. Alternatively or in addition, a duration of the cycle 510 is not fixed. The cycle duration varies depending on the traffic characteristics, e.g., the currently outstanding access requests and/or their access parameters. Alternatively or in addition, the cycle duration depends on a network setup. The network setup may include at least one of network size, network topology and network configuration at the access point 100. The access point 100 carries out the beacon transmission 304 in a broadcast manner. Each of the nodes 200 in the vicinity of the access point 100 receives the beacon frame according to the step 404.

The beacon frame transmission 304 and its reception 404 mark the start of the cycle 510. The cycle 510 includes the beacon transmission itself in the phase 504, the contention phase 502 and the schedule-based radio access phase 506 for data exchange.

The beacon frame contains information specifying the assignment of the time slots for the schedule-based access to be exercised in the subsequent cycle. The time slot assignment is carried out in a dynamic fashion based on the indication of individual traffic characteristics by the nodes 200 in the contention phase 502 by means of the access requests. The access requests may also be referred to as traffic indication frames.

In the schedule-based access phase 506, each of the nodes 200 strictly follows the assigned one or more time slots for data exchange. The assignment of the time slot is not fixed. E.g., the time slot assignment varies from cycle to cycle. All the nodes 200 are required to receive the beacon frame containing a schedule for the time slot assignment in the subsequent cycle.

The beacon frame transmission also enables the nodes 200 to implicitly time synchronize with the access point 100. This allows using more accurate clock crystals only for the access point 100, while less accurate crystal oscillators may be used at the nodes 200. As a result, the nodes 200 can be manufactured less expensively, can be more compact and/or can consume less power.

Any jitter accumulated over time at the nodes 200 can be compensated based on the beacon frame transmission 304. Since the elapsed time between consecutive beacon frames is short compared to a stability of the clock at the node 200, a timing drift developed over the cycle duration at the node remains insignificant for the data exchange 406 in the third phase 506.

Each of the nodes 200 has the possibility of switching to a power-down mode during foreign time slots (i.e., time slots assigned to other nodes 200 and/or time slots within which the nodes is neither transmitter nor receiver), which reduces power consumption. Reducing power consumption is fairly important for battery-operated nodes 200, e.g., in the context of many MTC applications. Alternatively or in addition, the nodes 200 may stay in the power-down mode in the contention phase, e.g., if they do not have any access request for data exchange.

The beacon transmission 304 in the second phase 504 also allows unassociated nodes 200 to receive the timing information according to the step 404 in the cycle 510 for the subsequent cycle 510. Based on the timing for the subsequent cycle 510, the unassociated node 200 contends to indicate its traffic characteristics according to the step 402 in the first phase 502 of the subsequent cycle 510 and, thereby, associate with the access point 100.

If the number of nodes 200, e.g., the number of requesting nodes 200 and/or the number of associated nodes 200, increases beyond a certain configurable threshold, the access point 100 broadcasts, e.g., in the second phase 504, a contention schedule defining the group contention in the first phase 502. In a variant, the contention phase 502 may be subdivided into multiple frequency resources for the group contention.

The contention phase 502 allows individual nodes 200 to indicate their traffic characteristics to the access point 100. The contention-based access may also be referred to as a random access. The step 402 may be implemented according to existing contention-based (e.g., random) access schemes.

In one implementation, the nodes 200 control the step 402 according to carrier sense multiple access with collision avoidance (CSMA/CA), which may also be referred to as listen-before-talk (LBT) control, to send the traffic indication frame according to the step 402. Upon receiving the traffic indication frame in the step 302, the access point 100 accordingly assigns time slots to the nodes. The time slot assignment information is embedded in the subsequent beacon frame according to the step 304.

Only nodes 200 that need to exchange (e.g., transmit) data carry out the traffic indication frame transmission from the node 200 to the access point 100 according to the step 402.

The traffic indication frame is relatively short (i.e., requires a short air-time), e.g., compared to the corresponding data exchange, which leads to an efficient radio access using the contention-based radio access. Thus, the technique can overcome the problem of a purely contention-based radio access network that becomes inefficient when the data traffic loads increase. In other words, the technique can be implemented to combine advantages of contention-based radio access requests with schedule-based data exchange, and to offset disadvantages of the two approaches as such.

Fig. 6 schematically illustrates different phases in time and frequency for

implementing the technique using more than one frequency channel. The assignment refers to a radio resource, i.e., a combination of time slot and frequency channel. Using more than one frequency channel allows satisfy further traffic QoS

requirements.

The medium access procedure is divided into the three distinct phases namely, beacon transmission phase 504, contention phase 502 and schedule-based access phase 506. These three phases are collectively referred to as a cycle 510. A temporal length of the cycle 510 is not fixed and varies, e.g., depending on the received access parameters, traffic characteristics and/or network setup.

While radio communication for beacon transmission in the second phase 504 and radio communication for contention in the first phase 502 use a common frequency channel 512 (also referred to as a primary channel or control channel), the schedule- based access in the third phase 506 is carried out across multiple available frequency channels, optionally including the primary channel 512. An example for an additional channel used in the third phase 506 is shown at reference sign 514 in Fig. 6.

In many practical MTC applications, especially for wireless industrial automation (WIA), reliability can be assured through advanced physical layer schemes involving multiple antennas at the access point 100, while the dominating device-to-device (D2D) communication performed by the nodes 200 does often not benefit from advanced antenna systems, e.g., due to deployment and cost constraints. Using multiple frequency channels 512 and 514 for D2D communication in the third phase 506, a medium access control algorithm according to the methods 300 and 400 can achieve communication reliability.

In some applications, the deployment constraint comes from the fact that sensors and actuators are often small in size and dimension. The spatial extent of such nodes is thus too limited to benefit from spatial diversity or antenna diversity. Since the radio wavelength determines the "smallness", the deployment constraint becomes less pronounced as the frequencies of the channels increase. On the other hand, undesired propagation properties (strong shadowing, blocking, etc.) limit the frequencies, e.g., in factory automation applications. For example, a sub 6 GHz-band is in commercial usage, wherein a multi-antenna system may be implemented for the linear dimension of the node being at least 10 cm.

By assigning a varying number of one radio resource 606 or more radio resources 608 in the third phase 506 to a requesting node 200, optionally including information on the multiple-radio resource assignment in the broadcast message 604 to particular nodes, the reliability of the data exchange is dynamically adjusted. A radio resource in a first time slot assigned to a particular node 200 and optional additional radio resources in respective later time slots assigned to the same node 200 are generically indicated by reference signs 606 and 608, respectively. The radio resource in the first time slot for the th node 200 is indicated by 606- The one or more radio resources in the later time slots for the th node 200 are indicated by 608-y:

By assigning multiple frequency channels 512 and 514 to a requesting node 200, latency bounds for time-critical traffic can be satisfied. By way of example, the number of time slots 606, 608 and/or the number of frequency channels 512, 514 over which the time slots are spread depend on the number of available channels, individual traffic characteristics and/or overall traffic characteristics. The individual traffic characteristics may be indicated by the access parameters for the data to be exchanged, e.g., including priority levels, addressing information (such as a source and/or one or more destinations for unicast, multicast and broadcast traffic) and a number of transmitting nodes. The overall traffic characteristics (such as traffic load) may be derived by combining the received access parameters and/or a network status.

The transmission according to the step 304 is carried out by an access point 100 in the broadcast manner. A broadcast message 604 (e.g., a beacon frame) is received by all the nodes 200 in the vicinity of the access point 100. The beacon transmission 304 is always carried out in the primary channel 512 of the multiple frequency channels.

The broadcast message 604 contains the radio resource assignment information for schedule-based data exchange to be exercised in the subsequent cycle according to the step 306. The radio resource assignment information is indicative of time slot duration and frequency channel, and optionally of the node 200 owning the time slot (e.g., the requesting node 200).

The radio resource assignment is carried out in a dynamic fashion based on the indication of individual traffic characteristics by the nodes 200 in the contention phase 502 of the preceding cycle and the number of available frequency channels.

For example, a set 610-1 of radio resources 606-1 and 608-1 is assigned to a first node 200. Another set of radio resources 606-2 and 608-2 is assigned to a second node 200. A further set 610-3 of radio resources 606-3 and 608-3 is assigned to a third node 200.

In the schedule-based access phase 506 of the step 306, the nodes 200 strictly follow the assigned time slots in combination with the assigned frequency channels for data exchange. Since the radio resource assignment is not fixed (e.g., varying from cycle to cycle), all the nodes 200 are required to receive the beacon frame 604 containing a schedule indicative of the radio resource assignment for each subsequent cycle.

The nodes 200 have the possibility of switching to a power-down mode in foreign time slots (e.g., time slots during which data transmission and/or reception is not needed according to the step 306) and/or idle gaps, leading to power savings at the nodes 200. Power conservation is particularly important for battery-operated devices in the context of MTC applications. For example, nodes 200 without data to be exchanged may stay in the power-down mode except for the broadcast message 604 in the particular (e.g., preconfigured) frequency channel 512 used for the

transmission in the step 304.

Individual nodes 200 indicate their traffic characteristics to the access point 100 in the contention phase or first phase 502 using the contention-based random access scheme according to the step 302. The contention phase 502 is carried out in the same frequency channel 512 used for the broadcast transmission 304 in the second phase 504. Only those nodes 200 that need to transmit data carry out traffic indication frame transmission to the access point 100 according to the step 302. For example, a unicast transmission is carried out to the access point 100 only from nodes 200 having data to transmit. The schedule-based access in the third phase 506 allows nodes 200 to exchange data using the assigned radio resources 606 and, optionally, 608. The schedule- based access is carried out in the step 306 using multiple frequency channels (without being limited to the number of two frequency channels 512 and 514). The schedule-based access phase is flexibly tailored to any number of available frequency channels.

Fig. 6 schematically illustrates an implementation using a fixed length for all time slots 606 and 608 in the third phase 506, which allows contiguous time slots. In practical implementations, an allowance time for a channel switching operation may be taken into account. Typically, a duration of the channel switching operation is small compared to the duration of the time slots (and similar for different channels). Hence, time slots with fixed-length may be implemented in combination with a channel switching time.

Fig. 7 schematically illustrates an implementation using individual time slots 606 and 608 of variable lengths. For example, each of the radio resources 606-2 and 608-2 allocated to Node 2 includes a time slot that is longer than each of the time slots of the radio resources 606-1 and 608-1 allocated to Node 1 and/or each of the time slots of the radio resources 606-3 and 608-3 allocated to Node 3.

During the contention phase 502, the nodes 200 contend using the random access principle to transmit individual traffic indication frames as the access requests 602. Each of the traffic indication frames contains the access parameters indicative of at least one of data size, source, destination, priority level, etc. Based on the information gathered from all the nodes 200, the access point 100 assigns the radio resources to different nodes 200 for data exchange in the subsequent cycle.

Assigning multiple time slots in different frequency channels leads to higher reliability while satisfying strict latency constraint, e.g., for MTC applications. Redundant time slots increase reliability. Distributing the redundant time slots across different channels concurrently (e.g., when possible) allows staying in an allowed latency bracket. If redundant time slots are introduced in the same channel, reliability can be achieved, but the data exchange may last beyond an allowed latency bound. The radio resources are dynamically assigned and can be of variable duration depending upon the traffic characteristics.

Fig. 8 schematically illustrates an example for the cycle-interleaving functional dependency of the phases 504 and 506 on the phase 502. The traffic indication frames 602 sent in the first phase 502 of the r-th cycle 510 lead to the assigning of the time slots 606 in the third phase 506 of the subsequent ( r+l)-th cycle 510, e.g., as broadcasted by the beacon frame 604 in the second phase 504 of the ( r+l)-th cycle 510.

In the example illustrated in Fig. 8, the Nodes 1, 3, 4 and 6 send traffic indication frames in cycle k. Corresponding to the traffic indication frames, the access point 100 assigns time slots (i.e., radio resources distributed in a single channel) to these nodes in cycle k+1. The time slots can be of different durations and the time slot durations are assigned based on the indicated priority levels, optionally in

conjunction with the order in which the traffic indication frames are transmitted. As indicated in Fig. 8, Node 2 has traffic in cycle rand does not have data traffic in cycle k+1.

Each traffic indication frame contains the information that is necessary for assisting the access point 100 in assigning time slots to the nodes 200 requiring data exchange. The traffic indication frame includes, e.g., as the access parameters, information on traffic priority and QoS requirements, size of the data to be exchanged, a source address and one or more destination addresses (i.e., information related to unicast, multicast or broadcast transmission), etc.

Since the contention phase 502 uses contention-based access, it remains efficient for a certain number of contending nodes 200. If the number of contending (or requesting) nodes 200 grows further, e.g., if the number of contending nodes 200 exceeds a certain threshold, traffic indication frames may potentially suffer a higher number of collisions, and the medium access does not remain very efficient. In order to avoid this situation, subsets of nodes 200 are grouped for the group contention.

The contention phase 502 is divided according to the number of groups into the contention intervals. Nodes 200 belonging to one of the groups are allowed to contend by sending their access requests in the step 402 only in the contention interval allocated to their group. In this way, the number of potential contending nodes 200 is reduced at a given point of time. Thus, medium access for the transmission of traffic indication frames in the first phase 502 is efficient. The schedule for groups of nodes in the contention phase is coordinated by the access point 100. The grouping of the nodes 200 (also referred to as contention group assignment) and the allocation of the contention intervals for the contention groups are controlled or performed by the access point 100. Any change in the contention group assignment and/or the contention interval allocation is sent (e.g., as an incremental update) in the broadcast message (e.g., in the beacon frame). An extra contention interval can be reserved in anticipation for unassociated nodes. The contention phase 502 may be flexibly scheduled. An access point 100 may exercise a suitable prediction or learning scheme to assess the traffic demands indicated by the access requests, and adapt the schedule and/or the duration of the contention phase 502 accordingly.

The schedule-based access in the third phase 506 allows the nodes 200 to exchange data in the assigned time slots. The node-specific time slots are assigned dynamically and can be of variable duration.

Fig. 9 illustrates a non-limiting simple radio resource assignment using three frequency channels 512, 514 and 516. The nodes 200 include Nodes 1, 3, 4 and 6 sending traffic indication frames in the cycle raccording to the step 402.

Corresponding to the traffic indication frames, the access point 100 assigns time slots to these nodes in cycle r+1 in different frequency channels according to the step 304. This information is broadcast to the nodes 200 in the beacon frame 604 transmitted in cycle r+1.

The time slots can be of any other duration, e.g., assigned based on the indicated priority levels, source/destination information and data size instead of the order in which the traffic indication frames are transmitted in the step 402. It can be observed from Fig. 9 that, for instance, Node 2, which has traffic in cycle k, does not have data traffic in cycle r+1.

Moreover, the time slots assigned to a particular node (irrespective of whether the particular node is transmitting or receiving) do not overlap in different frequency channels. In order to ensure this constraint, there can be empty periods on a given frequency channel. As an example, the first time slot in the frequency channel 512 for Node 4 causes a gap in the frequency channel 514 until the first time slot is over plus an additional delay for tuning Node 4 to the frequency channel 514.

Fig. 10 schematically illustrates a schedule for the third phase 506. The time slot 704 allocated to Node 2 is longer than the time slot 702 allocated to Node 1. Alternatively or in addition, Node 1 and Node 2 transmit multiple unicast data frames, e.g., to the access point 100 or another node 200. Node 2 is able to send three data frames in its time slot 704 compared to Node 1 that transmits two data frames. The data exchange in the third phase 506 may be bidirectional. The second direction may be used for a response including further data or an acknowledgment signal 706, as illustrated in Fig. 10. Payload data may be transmitted from source to destination in one direction and the acknowledgment signal 706 may be transmitted from destination to source in the opposite direction. In the case of multicast or broadcast transmissions, no acknowledgment signals 706 (e.g., no ACK frames) are

transmitted.

The time slots 702 and 704 are assigned based on the indicated traffic demands in the contention phase 502. Consequently, the time slots 702 and 704 are always occupied. In other words, the hybrid access scheme including contention and scheduling rules out the downside of conventional schedule-based access network with pre-assigned time slots that are wasted, if there is no data to transmit.

The order and the duration of time slots 702 and 704 can be controlled by the access point 100. This allows implementing customized rules for fulfilling the traffic QoS in the radio access network.

The access point 100 has knowledge of individual instantaneous traffic characteristics (e.g., as to QoS, data size, etc.), as indicated in the contention phase 502 by the nodes 200. For a pre-configured granular level (e.g., in terms of time or number of nodes), the access point 100 sums up the traffic requirements (e.g., the data size) for each QoS class. Based on the summation, the access point 100 assigns the time slots.

By way of example, earlier time slots in the cycle 510 may be assigned to those nodes 200 having higher traffic priority, e.g., to minimize latency of the data exchange. Alternatively or in addition, if one or more nodes 200 have low priority traffic with large traffic volumes (e.g., a software update, log dumps, etc.), and one or more other nodes 200 have high priority traffic, the access point 100 determines to compromise nodes with low priority traffic and favor nodes with high priority traffic. In an extreme case, e.g., in anticipation of further high priority traffic, the access point 100 may determine to assign no time slots to nodes with low priority traffic in the next cycle 510 and instead assign them time slots in later cycles 510. Such a strategy can achieve low latency for high priority traffic. Fig. 11 schematically illustrates a data frame structure in the third phase 506 for an implementation using at least two frequency channels 512 and 514. In each time slot, the corresponding node 200 sends multiple data frames. For example, Node 2 sends three data frames in each of its time slot periods on both frequency channels compared to Node 1, which transmits only two data frames per cycle and frequency channel.

In the implementation for the radio access protocol 500 illustrated in Fig. 11, Node 1 and Node 2 transmit multiple unicast data frames in their respective time slots across the frequency channels 512 and 514. While assigning the radio resources, the access point 100 makes sure that each of the nodes can be active as either a transmitter or a receiver at a given time in a given frequency channel.

In any embodiment, the radio resources 606 and, optionally, 608 may be assigned by the access point 100 based on the overall gathered requirements from individual nodes 200 in the contention phase 502 on traffic characteristics (e.g., load, priority, source/destination information, etc.) and the available frequency channels (e.g., the channels 512 and 514). Alternatively or in addition, the access point 100 takes into consideration its own traffic and/or pending requests for radio resource assignment (e.g., from a previous first phase 502). The on-demand radio resource assignment according to the methods 300 and 400 can avoid the downside of conventional schedule-based systems, namely wasting pre-assigned radio resources when there is no data to be exchanged.

The assignment of multiple radio resources to one node 200 (e.g., a radio resource set including multiple time slots) ensures reliability that can be dynamically governed by the access point 100 and flexibly adjusted based on the availability of frequency channels, e.g., so as to achieve a level of reliability and a traffic QoS demanded by the access parameter.

The nodes 200 may request data exchange with different priorities. The radio resources are assigned for mixed-priority traffic across two or more frequency channels 512 and 514.

Fig. 12 schematically illustrates a non-limiting example for a system including Node 1 and Node 2 having higher priority traffic compared to Node 3 and Node 4. For example the data to be exchanged by Nodes 3 and 4 has lower reliability and/or less stringent latency requirements compared to the data exchanged by Nodes 1 and 2. Node 1 and Node 2 are assigned earlier radio resources 606-1 and 606-2 (i.e., earlier time slots), respectively, compared to the radio resources 606-3 and 606-4 assigned to Node 3 and Node 4, respectively.

Alternatively or in addition, additional radio resources 608-1 and 608-2 (i.e., additional time slots) across the two channels 512 and 514 are assigned. The additional radio resources 608 are also referred to as repetitive radio resources (or repetitive time slots). The redundant data exchange using the additional radio resources 608 ensures higher reliability.

Using multiple frequency channels allows spreading the multiple radio resources 606- y ^' and 608-/ for the /th high-priority node, so that the additional time slots of the /th node (such as the Node 2 in Fig. 12) do not block the data exchange of one or more other high-priority nodes (such as the Node 1 in Fig. 12).

Hence, the spreading of multiple time slots over different frequency channels can achieve high reliability with low latency, e.g., for aperiodic traffic. For example, assigning earlier radio resources and frequency-shifted repetitive radio resources 608 can lead to lower latency as compared to the latency sufficient for Node 3 and Node 4, each of which is assigned a radio resource 606 with a single time slots.

Hence, implementing the technique for multiple frequency channels allows exercising priority management in a flexible manner on a dynamic basis.

As a non-limiting example, nodes 200 with high-priority data can be assigned multiple (i.e., repetitive) time slots to ensure a high degree of reliability. While assigning time slots in the same channel induces unwanted latency, the access point 100 assigns multiple time slots in different frequency channels. When assigning the time slots in different channels, the access point 100 makes sure that a time slot for a first radio resource 606 assigned to a node in a particular frequency channel does not overlap in time with a time slot for a second radio resource 608 in another frequency channel assigned to the same node 200. As a result, the node 200 does not have to act as a transmitter or a receiver at the same time in different frequency channels. For example, a transceiver at the node 200 may be configured for a single frequency channel. The transceiver is tuned to the respective frequency channel at the assigned time slots. Fig. 7 illustrates that, in order to avoid overlapping time slots in different frequency channels, Node 2 waits for a short amount of time in frequency channel 514 before carrying out data transmission using the radio resource 608-2. As another example shown in Fig. 9, in the set 610-1 of radio resources allocated to Node 1, the first and second radio resources in the set are temporally contiguous without overlap.

Optionally, the source address and the one or more destination addresses of the data exchange are gathered during the contention phase 502. In this way, D2D communication patterns can be supported which further leads to lower latency as the data communication is not relayed through the access point 100 (e.g., a base station).

As another non-limiting example, nodes 200 having higher-traffic priority may be assigned earlier time slots, in a cycle and/or in earlier cycles, to minimize the latency for the data exchange 306. For instance, with earlier slot assignment, there is lower data communication latency for Node 1 compared to Node 2, as illustrated in Figs. 6 and 7.

Fig. 13 shows a flowchart for an implementation of the method 300. A step 303 of determining the time slot assignment is performed based on the access requests received in the step 302 and prior to the broadcasting step 304, e.g., at the end of the current cycle 510. Optionally, the step 303 is performed prior to the third phase 506. The steps are repeated, as indicated in Fig. 13, which gives rise to the cycles 510, e.g., as illustrated in Figs. 5 to 12.

During the contention phase 502, the access point 100 listens to the traffic indication frames from the nodes 200 according to the step 302. Based on the indicated traffic characteristics, the access point 100 calculates the time slot assignment for the nodes 200 in the step 303. The time slot assignment is also based on the overall traffic characteristics from the nodes 200 and, optionally, the traffic requirements from the access point 100 itself.

After the contention phase 502, the access point 100 can be involved in the data exchange process in the step 306 depending upon the source and the one or more destinations for data traffic. In the step 304, the access point 100 transmits the time slot schedule calculated in step 303, e.g., in the broadcast beacon frame. Fig. 14 shows a flowchart for another implementation of the method 300 from the point of view of an access point 100. The access point 100 is tuned to the primary channel 512 in a substep 301 of the step 302. During the contention phase 502 in the step 302, the access point listens to the traffic indication frames from terminal nodes 200.

Based on the indicated traffic characteristics, source and/or destination information, traffic priority and available frequency channels, the access point 100 calculates the time slot assignment across different frequency channels for the terminal nodes 200 in the step 303. The time slot assignment is based on the overall requirements and constraints from all the nodes in the radio access network, including the access point 100 itself, and any previous access requests that have not yet been granted and/or responded to in the latest beacon frame transmission.

After the contention phase 502, the access point 100 can be involved in the data exchange process depending upon the source and destination(s) for the data traffic in the step 306. Before carrying out the data exchange, the access point 100 switches to the scheduled frequency channel at the beginning of the slot in a substep 305 of the step 306.

Unless beacon transmission time is reached, the access point 100 is involved in data exchange or surveys the data exchange. When the beacon transmission time is reached, the access point switches to the frequency channel for beacon transmission in the step 304 and transmits the beacon frame. The beacon frame contains a schedule for the time slot and frequency channel, as calculated in the step 303.

Fig. 15 shows a flowchart for an implementation of the method 400. Upon listening to the beacon frame in the step 404, the node 200 knows the timing characteristics, e.g., the timing synchronization for the cycle 510 and the time slots potentially assigned to the node 200 in the current cycle 510.

The time slot for downlink traffic (i.e., from the access point 100 to one or more nodes) can be indicated directly in the beacon frame. There is no need for sending a traffic indication frame for downlink traffic (using contention-based access). The downlink traffic can be unicast, multicast or broadcast (e.g., in a similar fashion as the traffic originating from one of the nodes, including uplink traffic to the access point). In order to reduce power consumption, at least some of the nodes 200 switch to a low-power mode in unassigned time slots in a step 906. Since the time slot assignments and the time slot durations (and optionally the cycle duration) can change from cycle to cycle, the nodes 200 are required to enable reception in a step 910 for listening to the beacon frame in every cycle, e.g., upon expiry of the cycle duration determined at branching point 908.

The node 200 listens to the beacon frame in the step 404. The beacon frame contains all the relevant timing information regarding the time slots, contention- based access for the subsequent cycle (and optionally the subsequent beacon transmission, e.g., if the cycle is not periodic).

If there is traffic to be transmitted in a step 902, the node 200 sends out a traffic indication frame in the step 402 using the contention-based access. Based on the time slot information indicated in the previous cycle, the node 200 exchanges data in its assigned one or more time slots in the step 406.

For the rest of the time slots, as determined by the "no" branch of branching point 904, the node 200 switches to the low-power mode in the step 906. During the low- power mode, the node 200 constantly checks if the beacon transmission time is reached and/or if its data exchange time slot is reached in the branching point 908. When the beacon frame is scheduled to be transmitted, the node 200 switches to reception mode in the step 910 and receives the beacon frame in the step 404.

Fig. 16 shows a flowchart for another implementation of the method 400 executed by the terminal nodes 200 using multiple frequency channels. Like reference signs correspond to the steps of the implementation shown in Fig. 15.

A terminal node 200 switches to the frequency channel 512 on which the beacon frame is transmitted in a substep 403 of the step 404 and listens to a beacon frame in the step 404. The beacon frame contains all the relevant timing information, such as the time slots in conjunction with the frequency channel to be used for the data exchange in the corresponding time slot. Optionally, the beacon frame contains timing information for the contention-based access in the subsequent cycle and/or the subsequent beacon transmission.

If there is traffic to be transmitted, the terminal node 200 sends out a traffic indication frame in the step 402 using the contention-based access. The traffic indication frame contains information such as the source and destination addresses, data size, traffic priority, etc. Based on the time slot and frequency channel information indicated in the previous cycle, the node switches to the assigned frequency channel in a substep 405 of the step 406 and exchanges data in the step 406.

Fig. 17 shows a schematic block diagram for a device 1000 for providing access to a radio access network. The device 1000 comprises an interface 1002 for radio communication with nodes. Memory 1006 including the modules 102 to 106. One or more processors 1004 are coupled to the interface 1002 and to the memory 1006 for performing the functions of the modules 102 to 106.

Fig. 18 shows a schematic block diagram for a device 1100 for requesting access to a radio access network. The device 1100 comprises an interface 1102 for radio communication with an access point and, optionally, one or more nodes. Memory 1106 including the modules 202 to 206. One or more processors 1104 are coupled to the interface 1102 and to the memory 1106 for performing the functions of the modules 202 to 206.

The technique may be implemented to support variable traffic with efficient resource utilization. The technique may implement a hybrid approach for the radio access, wherein contention-based radio access and schedule-based data exchange are combined.

Embodiments of the technique may be highly flexible and adaptable to variable traffic demands as represented by the access requests and may effectively address traffic Quality of Service (QoS) parameters as represented by the access parameters. Based on the access requests, a variable number of nodes may be accommodated.

The technique allows, e.g., in a centrally controlled radio access network, managing the QoS traffic requirements at a granular level by means of the access point. The access point may exercise a multitude of traffic and priority management strategies.

At least some of the nodes may implicitly time synchronize with the access point, e.g., without requiring explicit control messages and/or without a highly accurate crystal oscillators at the node. Moreover, any newly appearing nodes, e.g., in the vicinity of the access point, may be accommodate or associate with the radio access network in a fairly easy manner. As has become apparent from above description of exemplary embodiments support variable traffic characteristics with efficient resource utilization. The benefits of schedule-based access and contention-based access schemes may be combined depending upon the instantaneous traffic demands and the number of nodes in a network.

Time slots of variable duration can be assigned to individual nodes based on their on-demand indication for traffic. The variable duration of time slots supports the nodes to cope with different volumes of traffic at a given time, e.g., in a burst traffic pattern. Unlike pre-assigned fixed time slots, on-demand assignment of time slots only to nodes requiring data exchange avoids wastage of time slots (i.e., idle time slots).

The terminal nodes can use explicit and/or minimally sized messages to indicate their traffic demands and traffic characteristics to the access point during the contention phase. Contention-based medium access for small sized messages only by nodes having traffic demands can be very efficient and can have a high degree of reliability.

At least some embodiments allow new nodes to easily associate themselves with a particular access point and, with low delays caused by control signaling, send and/or receive data.

An access point can directly manage traffic QoS requirements (e.g., priority levels) at a granular level. The access point may be able to assign time slots of durations corresponding to individual QoS demands of nodes. The order in which different time slots are assigned can be controlled. The time slot duration and slot assignment order may be governed by an access point based on the individual and overall traffic characteristics, optionally including the amount of traffic and priority levels, and the number of nodes.

The access point can assign time slots of durations and/or time slot repetitions corresponding to individual QoS demands of nodes. Assigning repetitive time slots achieves high reliability. While assigning repetitive time slots in the same channel could induce undesired delays, the access point can assign multiple time slots to the nodes in different channels. The time slot duration across different available frequency channels and the time slot assignment order can be governed by an access point, e.g., based on the individual and overall traffic characteristics. The radio resource assignment may be adapted to the number of frequency resources or channels available at a given time, e.g., considering the traffic requirements of the nodes and the access point itself.

The reliability of communicating the access requests and the broadcast message can be further increased by implementing multiple antennas at the access point to exploit space diversity gains to ensure high reliability for the communication from and/or to terminal nodes.

A large number of nodes can be associated with an access point efficiently. Subsets of nodes may be grouped for contention-based access, e.g., so that the number of contenders can be minimized at any given time, which in turn results in a potentially lower number of collisions and better radio resource utilization.

The broadcast message sent by an access point and containing time slot assignment information may be used for implicit time synchronization at terminal nodes, which can improve an effective data rate by reducing control signaling.

Many advantages of the present invention will be fully understood from the foregoing description, and it will be apparent that various changes may be made in the form, construction and arrangement of the equipments, modules, units and devices without departing from the scope of the invention and/or without sacrificing all of its advantages. Since the invention can be varied in many ways, it will be recognized that the invention should be limited only by the scope of the following claims.