Methods, systems, and devices for wireless communication based on ofdma digital modulation schemes

Abstract

A wireless network includes a plurality of access points having at least pairwise overlapping wireless coverage, each of the access points including an OFDMA modulation system and a channel scheduler coupled to the OFDMA modulation system, the channel scheduler configured to establish a number of virtual wireless interfaces for the access point, each virtual wireless interface associated with a dedicated set of subcarriers within an OFDMA frequency spectrum. At least a first one of the virtual wireless interfaces is configured to host all communication links between the access point and local mobile clients of the access point. At least a second one of the virtual wireless interfaces is configured to host a communication link between the access point and one of the neighboring access points.

Description

TECHNICAL FIELD

[0001] The present invention relates to methods, systems and devices for wireless communication based on Orthogonal Frequency Division Multiple Access (OFDMA) digital modulation schemes, in particular for dense wireless communication networks in industrial systems. BACKGROUND

[0002] Next generation wireless networks are expected to provide support for applications requiring low latency, high reliability and high throughput, such as for example indoor wireless systems in aircraft cabins, in particular for urban air traffic, but other application scenarios can be applicable as well. Low latency and high reliability are generally most useful for scenarios with multiple co-located wireless access points, which are often used to increase the potential deployment density and to extend the network coverage.

[0003] Wireless cabin applications aim at providing connectivity to the numerous devices onboard an aircraft without requiring extensive cabling or wiring. In such applications, several access points with overlapping coverage areas can be connected through a wired or wireless backbone.

[0004] In general, modern telecommunication standards, such as 5G or IEEE 802.1 lax, provide high reliability and high throughput, since these standards employ an Orthogonal Frequency Division Multiple Access (OFDMA) digital modulation scheme, enabling multiple users to maintain uplink and downlink communication links simultaneously. However, under the OFDMA traffic control scheme, interference between co-located access points cannot be avoided. Moreover, OFDMA alone cannot separate traffic from different applications from each other.

[0005] Prior solutions in the art involve coordinating traffic through time division means or contention control, neither of which is suitable for low latency systems, which are desirable for time-critical communications in applications such as for example fly-by-wireless applications.

[0006] Document US 8,000,604 B2 discloses an Orthogonal Frequency Division Multiple Access (OFDMA) based passive optical network architecture with dynamic bandwidth allocation.

[0007] Document US 7,936,836 B2 discloses a scheduling scheme for OFDMA parallel network architectures.

[0008] Document EP 2 030 473 B1 discloses a method for scheduling transmissions of multiple cells in a cluster of a wireless communication system by a joint scheduler of multiple base stations.

[0009] Document GB 2 571 005 A discloses a method of wireless communication in a wireless network comprising a physical access point and a plurality of stations partitioned into groups, each group being managed by a virtual access point implemented in the physical access point.

[0010] Document US 2010 / 0061470 A1 discloses a sliceable router having a forwarding engine and a plurality of virtual packet interfaces coupled to the forwarding engine, the virtual packet interfaces sharing an OFDMA-based programmable transceiver for interface virtualization.

[0011] Document US 2017 / 0289963 A1 discloses a method for allocating resource units in a wireless LAN. Document MX2010004611 A discloses a method for locally optimal resource allocation in communication of neighboring access points. SUMMARY

[0012] One of the objectives of the present invention is to improve latency and reliability of wireless communication in an OFDMA-based communication system having a plurality of access points.

[0013] At least some of these objectives are achieved by the subject-matter of the independent claims. Advantageous embodiments are described in the dependent claims related to the independent claims. Some or all of these objectives can also be achieved by other teachings incorporated into the present disclosure.

[0014] According to a first aspect of the present invention, a wireless network comprises a plurality of access points having at least pairwise overlapping wireless coverage, each of the access points comprising an OFDMA modulation system and at least one channel scheduler coupled to the OFDMA modulation system, the at least one channel scheduler being configured for establishing a variable number of virtual wireless interfaces of the access point, each virtual wireless interface being associated with a dedicated set of subcarriers within an OFDMA frequency spectrum. At least one first virtual wireless interface of the virtual wireless interfaces is configured for hosting all communication links between the access point and local mobile clients of the access point. At least one second virtual wireless interface of the virtual wireless interfaces is configured for hosting a communication link between the access point and one of the neighboring access points.

[0015] In some embodiments of the first aspect, each of the dedicated sets of subcarriers can be statically or dynamically configured by the at least one channel scheduler. In some embodiments of the first aspect, the at least one channel scheduler is configured for allocating subcarriers to the dedicated sets of subcarriers based on one of an IEEE 802.1q standard and an IETF DiffServ standard.

[0016] In some embodiments of the first aspect, each of the access points further comprises a queue management device coupled to the at least one channel scheduler, the queue management device comprising a plurality of packet queues, each of the plurality of packet queues being associated with one of the dedicated sets of subcarriers. In some embodiments thereof, the plurality of packet queues can comprise downlink queues and uplink queues.

[0017] In some embodiments of the first aspect, each of the access points is configured for operating in a half-duplex or full-duplex communication mode. In some embodiments of the first aspect, each of the access points is configured for emitting a detection beacon message for discovering neighboring access points and establishing at least one second interface of the virtual wireless interfaces based on responses to the detection beacon message received from neighboring access points.

[0018] According to a second aspect of the present application, a method for establishing a wireless mesh network comprising a plurality of access points having at least pairwise overlapping wireless coverage, the method comprising the steps of: defining a first virtual wireless interface of each of the plurality of access points for communication between the access point and local mobile clients of the access point by an OFDMA digital modulation scheme; defining at least one second virtual wireless interface of each of the plurality of access points for communication between the access point and one of neighboring access points in the wireless mesh network; allocating a first number of subcarriers within an OFDMA frequency spectrum to a first dedicated set of subcarriers; allocating a second number of subcarriers within the OFDMA frequency spectrum to a second dedicated set of subcarriers, wherein none of the second number of subcarriers is contained in the first number of subcarriers; providing a communication link between the access point and local mobile clients of the access point by the at least one first virtual wireless interface using the first dedicated set of subcarriers; and providing a communication link between the access point and one of neighboring access points in the wireless mesh network by the at least one second virtual wireless interface using the second dedicated set of subcarriers.

[0019] According to a third aspect of the present application, a method for establishing a wireless mesh network, the wireless mesh network comprising a plurality of access points having at least partially overlapping wireless coverage, the method comprising the steps of: defining a virtual wireless interface for each of the plurality of access points for communication between the access point and one of the neighboring access points having overlapping wireless coverage by an OFDMA digital modulation scheme; a first access point of the plurality of access points selecting a first number of resource units within an OFDMA frequency spectrum to allocate to a first set of dedicated resource units to provide a communication link to and from the first access point by the virtual wireless interface; the first access point of the plurality of access points sending a resource usage signal to a number of neighboring access points of the plurality of access points having overlapping wireless coverage with the first access point of the plurality of access points; and a second access point of the number of neighboring access points selecting a second number of resource units within the OFDMA frequency spectrum to allocate to a second set of dedicated resource units to provide a communication link to and from the second access point of the number of neighboring access points by the virtual wireless interface, wherein none of the second number of resource units are contained in the first number of resource units.

[0020] In some embodiments of the third aspect, the method further comprises the steps of: the second access point of the number of neighboring access points waiting for any amount of time within a resource allocation protection interval range from receiving the resource usage signal until selecting the resource allocation of the second number of resource units. In some embodiments thereof, the method further comprises the steps of: the second access point of the number of neighboring access points receiving another resource usage signal from a third access point of the plurality of access points during the waiting, the another resource usage signal indicating a third number of resource units; and selecting the second number of resource units such that none of the second number of resource units are contained in the first number of resource units or the third number of resource units. In some embodiments of the third aspect, a minimum protection interval of the resource allocation protection interval range is equal to a time required for an access point to select a resource unit and send the resource usage signal.

[0021] In some embodiments of the third aspect, the resource units can comprise one or more of available symbols within an OFDMA time domain, available subcarriers within the OFDMA frequency spectrum, and available transmit antennas of the access point.

[0022] One of the advantages of the present invention is that wired networks can be economically replaced by wireless networks while ensuring low-latency high-reliable communication. Advantageously, such wireless networks can still support a variety of traffic type sets and can be particularly useful for scenarios with multiple co-located access points with overlapping network coverage. Furthermore, wireless networks enable portability and mobility with respect to wired networks. Beneficial applications of the present invention involve Industry 4.0, control and assistance of autonomous driving vehicles, wireless cabin networks on board of aircraft and spacecraft operations, and distributed manufacturing, all of which require highly reliable communication links for safety-critical control systems.

[0023] The present invention allows implementing a mechanism that can allocate spectrum in frequency, time and space domain such that different access points can not only transmit at the same time but also avoid interference with each other and in communication with individual local clients. This advantageously enables the deployment of low-latency high-reliable wireless systems containing several overlapping access points that can be used to establish wireless mesh networks, each network node being able to provide local access to a large number of local clients.

[0024] Simultaneous transmission is ensured by giving higher priority to spectrum division in frequency and space domain. Time domain is used to ensure connectivity for all communication pairs in the wireless mesh network. By dedicating separate non-overlapping sets of subcarriers to different virtual wireless interfaces, communication can be established in the wireless network such that the wireless access points allow simultaneous communication with any of their neighbors and local clients without interfering with each other. BRIEF DESCRIPTION OF DRAWINGS

[0025] The present invention will be explained in greater detail with reference to the exemplary embodiments depicted in the drawings.

[0026] The accompanying drawings are included to provide a further understanding of the present invention and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the present invention and, together with the description, serve to explain the principles of the present invention. Other embodiments and many of the intended advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings. The elements of the drawings are not necessarily to scale relative to each other. Like reference numerals designate corresponding similar parts.

[0027] Figure 1 schematically illustrating a time-sensitive OFDMA network with multiple access points with overlapping wireless coverage according to some embodiments of the present invention;

[0028] Figure 2 schematically illustrating a block diagram of an exemplary implementation of an OFDMA-based access point according to some embodiments of the present invention;

[0029] Figure 3 a flowchart illustrating a method for establishing an OFDMA-based wireless mesh network according to some embodiments of the present application; and

[0030] Figure 4 a flowchart illustrating a method for resource unit allocation in an OFDMA-based access point according to some embodiments of the present application.

[0031] In the drawings, like reference numerals refer to like or functionally similar items throughout the several views. Any directional terms, such as "top," "bottom," "left," "right," "above," "below," "horizontal," "vertical," "back," "front," and the like are used with reference to the orientation of the embodiments as shown in the drawings and are merely used for purposes of explanation. No inference should be drawn from the use of these directional terms that the embodiments are intended to be in any specific orientation. DETAILED DESCRIPTION

[0032] While particular embodiments have been shown and described herein, it will be appreciated by those skilled in the art that, notwithstanding the specific embodiments that have been shown and described, various modifications and / or equivalent arrangements can be substituted for the specific embodiments shown and described without departing from the scope of the present application. The application is not limited to the embodiments that have been shown and described, but extends in scope to any modifications or alterations within the scope of the embodiments discussed herein.

[0033] A wireless network in the sense of the present disclosure refers to a network system based on the Orthogonal Frequency-Division Multiple Access (OFDMA) digital modulation scheme. OFDMA is an access point (AP)-centric topology that enables 802.11ax-based APs to communicate with multiple devices simultaneously by splitting each radio frequency channel into sub-channels, also referred to as resource units (RUs). OFDMA is a multi-user variant of the OFDM scheme, in which multiple access is achieved by assigning subsets of subcarriers to different users, allowing multiple users to transmit data simultaneously. In OFDMA, RUs are divided in two dimensions according to time and frequency, i.e., into an integer number of OFDM symbols and a certain number of contiguous or non-contiguous subcarriers, respectively. The grouping of subcarriers into RUs is referred to as subchannelization. The subcarriers that form a RU do not need to be physically adjacent. In the downlink, RUs can be allocated to different users. In the uplink, users can be assigned one or more RUs.

[0034] Since each individual RU can be used to serve different clients simultaneously, the AP can decide on its own how to allocate the sub-channels. For example, the AP can allocate the entire channel (i.e., all sub-channels within the channel's bandwidth) to a single user for a given timeframe, or it can divide the channel bandwidth into various sections of bandwidth ranges in order to serve multiple devices simultaneously. OFDMA improves the flexibility of allocating the available throughput to all devices connected to the AP.

[0035] Generally, a wireless network architecture includes more than one AP that are able to communicate with each other. Conventional OFDMA systems provide only a single air interface that is independent of the type of devices being served. In particular, the APs are not able to distinguish between local clients and neighboring APs at the interface level. Thus, the assignment of RUs for allocating bandwidth does not take into account the difference between inter-AP communication (communication between APs) and intra-AP communication (communication between an AP and its locally connected clients).

[0036] To more consistently benefit from the scheduling and allocation capabilities in OFDMA-based modulation systems, it is useful to minimize the use of contention-based traffic control and move towards scheduling-based traffic control. This requires the APs to be able to distinguish between neighboring APs and local clients. Thus, the solution described in this disclosure relies on the concept of virtual interfaces (VIs) that can be assigned different sets of resource units.

[0037] Figure 1 A schematic illustration of a time-sensitive OFDMA network 100 is shown. The time-sensitive OFDMA network 100 includes a plurality of access points A, Al, and A2 that have at least partially overlapping wireless coverage. For example, the wireless coverage perimeter Cl of access point Al overlaps with the wireless coverage perimeter C2 of access point A2. Access point A is located within both the wireless coverage perimeter Cl of access point Al and the wireless coverage perimeter C2 of access point A2, and thus has overlapping wireless coverage with the other two access points. Access points with overlapping wireless coverage perimeters can be referred to as neighboring access points.

[0038] Although, for reasons of clarity and conciseness, Figure 1 Only three access points A, Al, and A2 are explicitly shown in FIG. 1, but it should be clear that more than three access points can be used to create a wireless mesh OFDMA network 100 of more than one dimension. For example, the access points can form a two-dimensional grid with partially overlapping wireless coverage. Such a two-dimensional grid can be regularly arranged, i.e., each access point within the grid has the same number of neighboring access points. In an alternative configuration, the two-dimensional grid can be irregularly shaped, i.e., the number of neighboring access points for each access point varies in an irregular manner along the edges of a graph representing the grid.

[0039] As Figure 2Each access point (AP) A, Al and A2 can comprise an OFDMA modulation system 7 that utilizes resource units (RUs) 9 within the available OFDMA spectrum 8 to enable communication on the physical and data link layers, as schematically shown. The OFDMA modulation system 7 is coupled to a channel scheduler 6 that is configured to establish a variable number of virtual wireless interfaces V, VI, V2, VL, VL1 and VL2 for the AP. Each virtual wireless interface is associated with a dedicated set of subcarriers within the OFDMA spectrum. A single channel scheduler 6 can be used for all virtual wireless interfaces V, VI, V2, VL, VL1 and VL2 of the AP. Alternatively, there can also be different channel schedulers 6 in the AP, each channel scheduler 6 being responsible for at least one virtual wireless interface. For example, a separate channel scheduler 6 can be implemented for each virtual wireless interface. Different types of virtual wireless interfaces can also have a dedicated channel scheduler 6. For example, a first channel scheduler 6 can be implemented for the virtual wireless interfaces that host the communication links between the AP and the local mobile clients L, LI and L2, and a second channel scheduler 6 can be implemented for all virtual wireless interfaces that are used for the communication links between the AP and all different neighboring APs. For the sake of clarity and ease of understanding, Figure 2 Only one channel scheduler 6 is explicitly depicted in Figure 2 Two or more channel schedulers 6 can also be implemented in the system of

[0040] To avoid interference between different communication links of the AP, at least one first interface of the virtual wireless interfaces is configured for all communication links between the hosting AP and the local mobile clients L, LI and L2 of the AP, i.e. so-called intra-AP communication. In contrast, at least one second interface of the virtual wireless interfaces is configured for the communication links between the hosting AP and one or more neighboring APs, i.e. so-called inter-AP communication. The channel scheduler 6 can statically or dynamically configure each dedicated set of subcarriers. For example, the channel scheduler 6 can assign subcarriers to the dedicated set of subcarriers based on one of the IEEE 802.1q standard and the IETF DiffServ standard (Internet Engineering Task Force Differentiated Services).

[0041] For each virtual wireless interface, a separate set of queues can be reserved in the queue management device 5 coupled to the channel scheduler 6. The queue management device 5 comprises a plurality of packet queues. For example, a first packet queue 5a for a first set of dedicated subcarriers can hold data packets for traffic in intra-AP communications. A second packet queue 5b for a second set of dedicated subcarriers can hold data packets for traffic in inter-AP communications. Depending on the needs of the respective communication channel, e.g. depending on whether the AP is in half duplex or full duplex communication mode, the queues 5a, 5b can each comprise a downlink queue and an uplink queue. In some embodiments, only virtual wireless interfaces hosting communication links between the AP and local mobile clients can be configured with a downlink queue and an uplink queue. Virtual wireless interfaces configured for hosting communication links between the AP and one or more neighboring APs can have one set of queues, each queue for a different type of traffic.

[0042] The inter-AP virtual wireless interface can be further distinguished from the intra-AP virtual wireless interface in that the inter-AP virtual wireless interface comprises traffic of all queues having the same destination, while the intra-AP virtual wireless interface can comprise queues having packets destined to or coming from different destinations, i.e. different local mobile clients. Thus, in case of the intra-AP virtual wireless interface, the channel scheduler 6 can also isolate traffic destined to or coming from different local mobile clients by separating such traffic into different queues.

[0043] A separate set of queues can be implemented for each virtual wireless interface. For example, separate sets of queues can be applied for different types of traffic. Each set of queues can then be mapped to a set of subcarriers represented by one resource unit.

[0044] The queue management device 5 can accept local requests from the local request interface 1 and relay them through the congestion admission controller 2 to avoid dropping of incoming data packets. For example, the congestion admission controller 2 can employ single rate admission with burst size control for DiffServ EF and CS5 classes. Whenever a new local client joins the AP, a service level agreement is negotiated between the AP and the local client. Thus, the quality of service level required by each client will be guaranteed as well as the consistency of the client behavior with the established service level agreements in the downlink as well as in the uplink. The relayed local requests can then be queued by the queue management device 5 in a first set of queues.

[0045] Similarly, the queue management device 5 can accept incoming traffic at the traffic interface 3, which can be classified and identified in the traffic classification device 4. The classified and identified data traffic packets can then be queued by the queue management device 5 in a second set of queues different and disjoint from the first set of queues. Thus, depending on the type of traffic, the queue management device 5 can apply different scheduling algorithms for the different sets of queues. For example, the queue management device 5 can apply a weighted round robin algorithm for the first set of queues and a strict priority algorithm for the second set of queues.Figure 2 The wireless mesh network 100 implemented using APs is not contention-based, but rather, is schedule-based.

[0046] To discover neighboring APs, the APs can be provided with the ability to emit a detection beacon message in a bootstrapping procedure. Based on responses to the detection beacon message received from neighboring APs, different virtual wireless interfaces can be established to accommodate necessary isolation and different inter-AP communication links between different APs within the wireless coverage perimeter of the AP emitting the detection beacon message.

[0047] Figure 3 A flowchart of a method M1 for establishing a wireless mesh network, such as the wireless mesh network 100 of Figure 1 is schematically illustrated. The method M1 can be implemented by a plurality of access points having at least pairwise overlapping wireless coverage, such as the access points illustrated and described in connection with Figure 1 and Figure 2 In a first step Ml 1, a first virtual wireless interface of each of the plurality of access points is defined for communication between the access point and a local mobile client L, LI or L2 of the access point by an OFDMA digital modulation scheme. Next, in a second step M12, at least one second virtual wireless interface of each of the plurality of access points is defined for communication between the access point and one of the neighboring access points in the wireless mesh network 100.

[0048] In step M13, a first number of subcarriers within an OFDMA frequency spectrum is allocated for a first set of dedicated subcarriers, while in step M14, a second number of subcarriers within the OFDMA frequency spectrum is allocated for a second set of dedicated subcarriers. The second number of subcarriers is mutually exclusive from the first number of subcarriers, i.e., none of the second number of subcarriers is contained in the first number of subcarriers.

[0049] In step M15, a communication link between the access point and the local mobile client of the access point can be provided using the first set of dedicated subcarriers by the at least one first virtual wireless interface, while in step M16, a communication link between the access point and one of the neighboring access points in the wireless mesh network 100 can be provided using the second set of dedicated subcarriers by the at least one second virtual wireless interface.

[0050] Figure 4 A flowchart of a method M2 for establishing a wireless mesh network is schematically illustrated, the method comprising resource unit (RU) allocation in an OFDMA-based access point. The method M2 can be implemented, for example, in an access point as illustrated and described in connection with Figure 1The wireless mesh network 100 described and illustrated is implemented. The wireless mesh network 100 to which method M2 is applicable includes multiple access points having at least paired overlapping wireless coverage, such as combined... Figure 1 and Figure 2 The access points A, A1, and A2 are described and shown.

[0051] Method M2 first involves step M21: defining a virtual radio interface for each of the multiple access points. The virtual radio interface is implemented in an OFDMA digital modulation scheme for communication between access points (APs). Specifically, the virtual radio interface can be used to establish inter-AP communication between the AP in question and one of its neighboring APs whose radio coverage overlaps with that of the AP in question.

[0052] All access points (APs) in the wireless mesh network 100 can be represented by a graph G = (V, E (V,RC)) describing the wireless connections of the network. V represents an AP, and E represents the edge set of connections to V within a certain distance or perimeter where the signal-to-noise ratio (SNR) of the wireless connections is greater than a predetermined threshold. This threshold can be obtained, for example, by configuring the transmission power of each AP based on the acceptance level. For instance, in an aviation wireless mesh network 100, the transmission power should be higher than a defined value to ensure reliable, permanent connections between network nodes.

[0053] In the second step M22, method M2 involves a first AP among multiple APs selecting a first number of Resource Elements (RUs) within the OFDMA spectrum and allocating them to a first dedicated set of RUs. These RUs in the first dedicated set are intended to provide a communication link to and from the first access point via the virtual radio interface. RUs may be associated with a certain number of available symbols in the OFDMA time domain, a certain number of available subcarriers in the OFDMA spectrum, and / or, in the case of MIMO, the available transmit antennas of the access point. The number of available time slots is equal to 2 for a half-duplex system and 1 for a full-duplex system. The number of available frequency subcarrier sets is equal to the total available spectrum divided by the minimum frequency to be allocated to each AP, minus the final guard band between the subcarrier sets. The number of available transmit antennas depends on the hardware configuration of the respective AP.

[0054] If a regular network of degree N exists, each AP has N*2 + 4 available RUs in a full-duplex system and N + 2 available RUs in a half-duplex system. For irregular graphs, the required number of RUs cannot be reliably based on the network's degree; therefore, a graph coloring method can be used to allocate RUs to each virtual wireless interface between APs (i.e., along the edge) and to each AP (i.e., from the outside to the vertex representing a node in the network). The RUs allocated to vertices are used by the APs for their respective connected local devices (such as…). Figure 1The devices L, L1 or L2 shown in the middle communicate.

[0055] The first AP can be a network gateway that collects the connectivity information of all APs in the wireless mesh network, e.g. based on a given communication protocol. The network gateway can estimate the number of available RUs as the product of the number of available symbols, the number of available subcarriers within the OFDMA spectrum and the number of available transmit antennas. Furthermore, the network gateway can determine from the network connectivity information whether the graph representing the wireless network topology of all APs is regular. To this end, the degree of each AP node is established based on the number of links / edges with a signal-to-noise ratio above a given threshold.

[0056] The network gateway as the first AP then first reserves two (half duplex) or four (full duplex) RUs for the communication of the local client with the first AP. A vector with all selected RUs is created, typically all available RUs are marked as unused. Once the first AP has selected the first number of RUs, it sends a resource usage signal to a number of neighboring APs in step M23. The resource usage signal comprises the vector with all RUs selected by the first AP. The APs with overlapping wireless coverage with the first AP will be able to receive the resource usage signal and mark the first number of RUs selected by the first AP as reserved as indicated. Thus, to avoid potential interference in the communication, one of the second APs of the number of neighboring access points will be able to select a second number of RUs in the OFDMA spectrum assigned to a second set of dedicated RUs. The second number of RUs is disjoint from the first number of RUs, i.e. none of the second number of RUs is contained in the first number of RUs.

[0057] If there is another AP in the vicinity of the first AP that also selects RUs upon receiving the resource usage signal, there can be a problem in selecting the second number of RUs: both receiving APs can unintentionally select a second number of RUs that are not disjoint, resulting in an unexpected interference in the selected common RUs. Thus, the method M2 can involve a step M24: each of the number of neighboring APs waits for an arbitrary amount of time. The arbitrary amount of time can be randomly selected within a resource allocation guard interval range. The resource allocation guard interval range starts at the point in time of receiving the resource usage signal and ends at the point in time of actually selecting the second number of RUs. The resource allocation guard interval range can have a fixed upper limit value and its minimum guard interval can be equal to the time required for the AP to select the RUs and send the resource usage signal.

[0058] Thus, if any second AP of the number of neighboring access points receives another resource usage signal from a third access point of the plurality of access points during the waiting period in step M25, the second AP will be able to take into account any RU additionally reserved by the other second AP when selecting its own number of RUs. The other resource usage signal indicates a third number of RUs, such that the selection of the second number of RUs can be performed under the boundary condition that none of the second number of RUs is contained in the first number of RUs (reserved by the first AP) or the third number of RUs (reserved by the other second AP whose waiting period happens to be shorter than the receiving AP).

[0059] The process of selecting further numbers of RUs for further APs is recursively repeated until all APs in the network have been allocated RUs for their respective virtual wireless interfaces. If the network is fully wireless, i.e. has no wired backbone to which the APs are connected, the RUs still available can be determined in a similar way as for the RUs used for intra-AP communication.

[0060] If the graph representing the wireless mesh network is regular, i.e. if the number of connections of each AP to neighboring APs in the main mesh of the network is equal, the RUs can be distributed in a deterministic algorithm: The graph can be run edge by edge starting with one network gateway as the first AP, stopping at each second node that has not yet been connected to any AP considered for the allocation of RUs. In any visited AP, a number of RUs is selected among the RUs not yet reserved for neighboring APs.

[0061] If the graph representing the wireless mesh network is irregular, i.e. if the number of connections of at least two APs to neighboring APs varies, the network gateway as the first AP creates a vector with all RUs not used for intra-AP communication. Then, the network gateway starts randomly selecting as the first number of RUs as many RUs as needed for the inter-outbound-AP communication link. The selected RUs are marked as used / reserved in the vector broadcasted in the resource usage signal. All neighboring APs in the connection graph will receive the broadcasted resource usage signal, can enter a waiting period of any, random length within the resource allocation guard interval (see above), and select a second number of RUs depending on the resource usage signals received from at least the first AP and eventually from other neighboring APs within the waiting period. The APs select as the second number of RUs as many RUs as needed for the inter-outbound-AP communication link from all available, i.e. unused and not yet reserved, RUs. If possible, the selected RUs should not be adjacent to used RUs, such that interference between different communication links is as small as possible. Then, a new resource usage signal with an updated vector of reserved RUs is broadcasted to the other neighboring APs.

[0062] The process continues until all APs in the wireless mesh network have established intra-AP communication links and inter-AP communication links. When following the above algorithm, all APs with overlapping wireless coverage will communicate with different communication partners (local clients and neighboring APs) over disjoint RUs. This will minimize interference between different communication links and guarantee low latency and high reliability, especially for the communication between APs.

[0063] In the foregoing detailed description, various features are grouped together in one or more examples for the purpose of streamlining the disclosure. This description is intended to be illustrative, and not restrictive. It is intended to cover all alternatives, modifications, and equivalents. Many other examples will suggest themselves to those of ordinary skill in the art having the benefit of the above description.

[0064] Embodiments were chosen and described in order to best explain the principles of the application and its practical application, to thereby enable others skilled in the art to best utilize the application and various embodiments with various modifications as are suited to the particular use contemplated. In the claims, the terms “including” and “in which” are used as the plain English equivalents of the respective terms “comprising” and “wherein.” Also, “a” or “an” are used as the plain English equivalents of “one or more” in this example.

Claims

1. A wireless network (100) comprising: a plurality of access points (A; Al ； A2) having at least pairwise overlapping wireless coverage (Cl; C2), each of said access points comprising: an OFDMA modulation system (7); and at least one channel scheduler (6) coupled to said OFDMA modulation system (7), said at least one channel scheduler (6) being configured for establishing a variable number of virtual wireless interfaces (V; VI; V2; VL; VLl; VL2) of said access points (A; Al; A2), each virtual wireless interface being associated with a dedicated set of subcarriers within an OFDMA spectrum, wherein at least one first interface (VL; VLl; VL2) of said virtual wireless interfaces is configured for hosting all communication links between said access point and local mobile clients (L; LI; L2) of said access point, wherein at least one second interface (V; VI; V2) of said virtual wireless interfaces is configured for hosting communication links between said access point and one of the neighboring access points, wherein a first access point of said plurality of access points (A; Al; A2) is configured for selecting a first number of resource units within the OFDMA spectrum to be allocated to a first dedicated set of resource units for providing communication links to and from said first access point through said at least one second interface (V; VI; V2) and for transmitting a resource usage signal to a certain number of neighboring access points of said plurality of access points having overlapping wireless coverage with said first access point of said plurality of access points, and wherein a second access point of said number of neighboring access points is configured for selecting a second number of resource units within the OFDMA spectrum to be allocated to a second dedicated set of resource units for providing communication links to and from said second access point of said number of neighboring access points through said at least one second interface (V; VI; V2) based on the received resource usage signal, wherein none of said second number of resource units is contained in said first number of resource units.

2. The wireless network (100) of claim 1, wherein Each of said dedicated sets of subcarriers is statically or dynamically configured by said at least one channel scheduler (6).

3. The wireless network (100) of claim 1 or 2, wherein Said at least one channel scheduler (6) is configured for allocating subcarriers to said dedicated sets of subcarriers based on one of the IEEE 802.1q standard and the IETF DiffServ standard.

4. The wireless network (100) of one of claims 1 to 3, wherein Each of said access points (A; Al; A2) further comprises a queue management device (5) coupled to said at least one channel scheduler (6), said queue management device (5) comprising a plurality of packet queues (5a; 5b), each of said plurality of packet queues being associated with one of said dedicated sets of subcarriers.

5. The wireless network (100) of claim 4, wherein Said plurality of packet queues (5a; 5b) comprises downlink queues and uplink queues.

6. The wireless network (100) of one of claims 1 to 5, wherein Each of said access points (A; Al; A2) is configured for operating in a half-duplex or full-duplex communication mode.

7. The wireless network (100) of one of claims 1 to 6, wherein Each of the access points (A; A1; A2) is configured for emitting a detection beacon message in order to discover neighboring access points and to establish at least one second interface (V; V1; V2) of the virtual wireless interface based on responses to the detection beacon message received from neighboring access points.

8. A method (M1) for establishing a wireless mesh network (100) comprising a plurality of access points (A; A1; A2) having at least pairwise overlapping wireless coverage (C1; C2), the method (M1) comprising: defining a first virtual wireless interface of each of the plurality of access points for communication (M11) between the access point and a local mobile client (L; L1; L2) of the access point by an OFDMA digital modulation scheme; defining at least one second virtual wireless interface of each of the plurality of access points for communication (M12) between the access point and one of the neighboring access points in the wireless mesh network (100); allocating a first number of subcarriers within an OFDMA frequency spectrum for a first set of dedicated subcarriers (M13); allocating a second number of subcarriers within the OFDMA frequency spectrum for a second set of dedicated subcarriers (M14), wherein none of the second number of subcarriers is contained in the first number of subcarriers; providing a communication link (M15) between the access point and the local mobile client of the access point using the first set of dedicated subcarriers by the at least one first virtual wireless interface; and providing a communication link (M16) between the access point and one of the neighboring access points in the wireless mesh network (100) using the second set of dedicated subcarriers by the at least one second virtual wireless interface, wherein a first access point of the plurality of access points (A; A1; A2) selects a first number of resource units within an OFDMA frequency spectrum to be allocated to a first set of dedicated resource units for providing a communication link (M22) to and from the first access point by the at least one second interface (V; V1; V2); and transmits a resource usage signal (M23) to a number of neighboring access points of the plurality of access points having overlapping wireless coverage with the first access point of the plurality of access points, and wherein a second access point of the number of neighboring access points selects a second number of resource units within the OFDMA frequency spectrum to be allocated to a second set of dedicated resource units based on the received resource usage signal for providing a communication link (M26) to and from the second access point of the number of neighboring access points by the at least one second interface (V; V1; V2), wherein none of the second number of resource units is contained in the first number of resource units.

9. The method of claim 8, further comprising: the second access point of the number of neighboring access points waiting for an arbitrary amount of time (M24) within a resource allocation protection interval range from receiving the resource usage signal until selecting the second number of resource units.

10. The method of claim 9, further comprising: a second access point of the number of neighboring access points receiving, during the waiting period, a further resource usage signal (M25) from a third access point of the plurality of access points, the further resource usage signal indicating a third number of resource units; and selecting the second number of resource units such that none of the second number of resource units is contained in the first number of resource units or the third number of resource units.

11. The method of claim 9 or 10, wherein, a minimum guard interval of the range of resource allocation guard intervals is equal to a time required for the access point to select a resource unit and transmit the resource usage signal.

12. The method of any one of claims 8 to 11, wherein, the resource units comprise one or more of available symbols within an OFDMA time domain, available subcarriers within the OFDMA frequency spectrum, and available transmit antennas of the access point.

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