NOMA / TDMA hybrid communications procedure for clustered ad hoc networks

Abstract

The invention relates to a method for determining the multiple access mode and scheduling of communication links in an ad hoc network comprising several nodes grouped into one or more clusters. It comprises: • a stage of transmitting information about the quality of the communication links to a decision node; • a stage of partitioning the communication links between those using NOMA-type multiple access and those using TDMA-type multiple access, according to a performance criterion; • a third stage of determining a timing schedule for the communication links, respecting the calculated multiple access types; • a fourth stage of transmitting the partitioning information and the timing schedule information to the nodes involved in the communication links. The invention also relates to a decision node that implements the method.

Description

Domaine technique :

[0001] The invention relates to the field of radio communications in so-called clustered ad-hoc networks. More specifically, it concerns a method for selecting a multiple access type for communication links in order to increase network throughput in various situations compared to a conventional TDMA (Traffic Domain Management) function. Time Division Multiple Access, or multiple access via time-sharing). Technique antérieure :

[0002] Ad hoc networks, or MANETs (English acronym for Mobile Ad hoc Network, ou réseau mobile ad hoc ) ,Ad hoc networks are wireless networks that do not rely on an infrastructure with fixed access points, unlike cellular networks. Each node in the network participates in data routing, retransmitting it to other nodes. The choice of nodes involved in a transmission is dynamic, based on network connectivity. Ad hoc networks are therefore self-configuring and dynamic networks, in which nodes are free to move. They are used when it is necessary to rapidly deploy a radio communications network in an area where cellular network infrastructure is insufficient or inaccessible. This can be the case, for example, for civil security forces (firefighters, police, ambulances, etc.) during sporting events or shows, special events or disasters, for airports, or for military personnel in the field of operations.

[0003] Ad hoc networks are expected to be deployed on a massive scale in future telecommunications networks, in order to create highly connected sub-bubbles to link connected objects. This is already the case with fifth-generation (5G) radio communications, where the concept of Flying Ad hoc networks (FANETs), or flying ad hoc networks, for drone control. VANETs (English acronym for Vehicular Ad hoc Network, or vehicular ad hoc network), are used to model road traffic management systems and information sharing between vehicles to improve road safety. SPAN networks (English acronym for SmartPhone Ad hoc Network, (or ad hoc network for smartphone) are ad hoc networks based primarily on Wi-Fi and Bluetooth technologies.

[0004] Within ad hoc networks, clusters are formed, which correspond to groupings of nodes, often based on proximity. Cluster allocations can be done via configuration (to create operational groups) or dynamically based on node proximity, capacity, and needs. Frequency resources (logical communication channels) are allocated to each cluster to minimize interference between clusters. Within a cluster, an elected node acts as the coordinator. This node is responsible for managing the cluster: adding or removing nodes, and allocating resources. Gateways can be created between different clusters to ensure connectivity for nodes across the entire network.

[0005] Within a cluster, resource allocation is generally performed using a TDMA (Transmission-Defined Multiple Access) scheme, where a frame, representing the transmission times of the nodes, is divided into intervals called slots, each assigned exclusively to a particular communication link. TDMA access ensures that the links communicate orthogonally without creating interference. The drawback is that the resulting throughput is suboptimal, as it does not account for the ability of multiple users to transmit simultaneously.

[0006] There are other access control techniques that can also be applied to ad hoc networks, in particular the multiple access techniques known as NOMA (English acronym for Non Orthogonal Multiple Access, or non-orthogonal multiple access). These techniques consist of combining power management at the transmitter and successive suppression of interference (in English, SIC for Successive Interference Cancellation ) at reception. They are used, for example, in LTE Advanced (English acronym for Long Term Evolution - Advanced, a cellular network standard), or in the ATSC 3.0 standard (English acronym for Advanced Television Systems Committee, digital television standard). NOMA-type multiple access systems have also been considered as relevant candidates for 5G applications.

[0007] NOMA-type multiple access techniques do not guarantee the absence of interference between communication links, but they process signals in such a way that the sources can be separated by the receiver. NOMA techniques allow multiple links to transmit simultaneously and are associated with precoding / decoding operations to eliminate interference at the receiver. If the precoder length (in terms of the number of TDMA slots) is less than the number of slots required to enable the same number of links to communicate using TDMA, then the overall throughput is increased. However, depending on the link configuration in the cluster, the NOMA solution may be less efficient than the TDMA solution (in terms of SNR, an acronym for Signal-to-Noise Ratio). Signal to Noise Ratio, or signal-to-noise ratio). Furthermore, it does not guarantee a minimum data rate. Therefore, it is not feasible to implement a communication method based solely on multiple access of the NOMA type without resorting to transmission power management processes for each node of the cluster, which are possible in the case of a cellular network but complex to implement within ad hoc networks.

[0008] One object of the invention is therefore to define a method for improving the overall throughput of an ad hoc network compared to a solution using TDMA network access, while guaranteeing a minimum throughput per link. To this end, the method described in the present invention proposes combining NOMA and TDMA access techniques in such a way as to leverage the best of both in every situation.

[0009] The paper RV Bhat, M. Motani, and TJ Lim, "Hybrid NOMA for an Energy Harvesting MAC With Non-Ideal Batteries and Circuit Power," in IEEE Transactions on Wireless Communications, vol. 18, no. 8, pp. 3961–3973, Aug. 2019, doi: 10.1109 / TWC.2019.2919827, describes a hybrid NOMA / TDMA communication system for a non-ad hoc communication system. In this paper, logical channel allocations for TDMA or NOMA communications are performed to maximize total throughput within power and battery consumption constraints. However, the calculations require knowledge of the instantaneous channel of all radio links, which is not necessarily possible for ad hoc networks due to potential rapid channel fluctuations, transmission latencies, and limited signal exchange capabilities.Furthermore, the solution is achieved using a computationally complex and suboptimal method (considering only a local optimum). The document WEI XINCHEN ET AL: "Resource Allocation Technique for Hybrid TDMA-NOMA System with Opportunistic Time Assignment", 2020 IEEE INTERNATIONAL CONFERENCE ON COMMUNICATIONS WORKSHOPS (ICC WORKSHOPS), IEEE, June 7, 2020 (2020-06-07), pages 1-6, XP033796254, also describes an example from the prior art.

[0010] Another object of the invention is therefore to propose a method for making decisions about the access system to be used and the scheduling of TDMA and NOMA accesses which is simple to implement, and requires little exchange within the network, in particular by not relying on knowledge of the instantaneous propagation channel of the radio links. Résumé de l'invention :

[0011] To this end, the present invention describes a method for determining a multiple access mode and scheduling for a plurality of communication links in an ad hoc network comprising a plurality of nodes grouped into one or more clusters, the communication links being operated on at least one logical channel. The method according to the invention comprises: a first step, implemented by the nodes, of transmitting information relating to the quality of the communication links to a node designated as the decision-making node; a second step, implemented by the decision-making node, of partitioning the communication links between communication links using NOMA-type multiple access and communication links using TDMA-type multiple access, based on a throughput criterion calculated from the information relating to the quality of the communication links transmitted in the first step; a third step, implemented by the decision-making node, of determining a temporal scheduling of the communication links on the common logical channel(s), respecting the multiple access types calculated in the second step; a fourth step, implemented by the decision-making node,of transmitting the partitioning information calculated in the second step and the temporal scheduling information calculated in the third step to the nodes involved in the communication links.

[0012] Depending on the implementation, the information relating to the quality of communication links is, for each communication link: statistical information on a propagation channel of the communication link, statistical information on interfering propagation channels, and a noise power level perceived by the receiving node of the communication link.

[0013] Advantageously, the second step of partitioning the communication links includes the implementation of an iterative algorithm comprising, for each communication link, the calculation of a user throughput using a TDMA-type multiple access mode, the calculation of a user throughput using a NOMA-type multiple access mode taking into account the multiple access modes used by the other communication links, and the selection of the access mode maximizing the user throughput of the communication link.

[0014] According to one embodiment of the process, the second step of partitioning the communication links comprises: a step to calculate a user throughput for each communication link when all communication links are associated with TDMA-type multiple access, a step to calculate a user throughput for each communication link when all communication links are associated with NOMA-type multiple access, a step to determine a set T N communication links associated with NOMA-type multiple access and a set T d of communication links associated with TDMA-type multiple access by comparing the respective user throughput for each communication link, iteratively, until convergence: a step to calculate a user throughput for each communication link in the set T N when only the communication links of said set T N use a NOMA-type multiple access, a step of searching for communication links belonging to the set T N for which the user throughput for a TDMA-type multiple access is greater than or equal to the user throughput for a NOMA-type multiple access, and the transfer of these communication links to the whole T d of communication links using TDMA-type multiple access.

[0015] According to a particular embodiment, the NOMA-type multiple access technique relies on the use of linear encoders / decoders, and the second step of partitioning communication links between communication links using NOMA-type multiple access and communication links using TDMA-type multiple access based on a throughput criterion includes the calculation of a size r linear encoder / decoder and encoding / decoding matrix calculation U and V adapted to the number of communication links using NOMA-type multiple access.

[0016] According to one embodiment, the third step of partitioning communication links includes defining a long time interval, or frame, divided into a plurality L short time intervals, or slots, and distribution of L slots between communication links in order to maximize the overall average throughput of the ad hoc communication network while ensuring a minimum throughput for each communication link.

[0017] According to a particular embodiment, LR 0 u R k φ slots are allocated exclusively to each communication link using TDMA-type multiple access, with R 0 u a minimum bandwidth constraint per link and R k φ a physical data rate associated with the communication link, LR 0 u R ¯ NOMA , min φ slots are allocated to communication links using NOMA-type multiple access, with the remaining slots distributed between communication links using NOMA-type multiple access and the communication link using TDMA-type multiple access with the physical throughput R k φ the highest.

[0018] Advantageously, the third step of communication link partitioning also includes the calculation of a frame length L * optimal considering the results of the second step of partitioning the communication links.

[0019] According to one embodiment, the method of determining a multiple access mode and scheduling according to the invention is implemented jointly on a plurality of clusters, by grouping their logical channels.

[0020] The invention also relates to a decision node in an ad hoc network comprising a plurality of nodes grouped into one or more clusters and implementing a plurality of communication links over at least one logical channel. The decision node includes computing means configured to implement: a first step of receiving information relating to the quality of communication links, a second step of partitioning the communication links between communication links using NOMA type multiple access and communication links using TDMA type multiple access, on a throughput criterion calculated from the information relating to the quality of communication links received in the first step, a third step of determining a temporal scheduling of said communication links on the logical channel(s), respecting the types of multiple access calculated in the second step, a fourth step of transmitting the partitioning information calculated in the second step and the temporal scheduling information calculated in the third step to the nodes involved in said communication links. Brève description des figures :

[0021] The invention will be better understood and other features, details, and advantages will become clearer upon reading the following description, given by way of example, and with the help of the accompanying figures, which are provided by way of example, and among which: there figure 1 represents an ad hoc network in which a method for determining a network access mode and scheduling according to the invention can be implemented; the figure 2 is a synoptic diagram of a method for determining a multiple access mode and scheduling according to an embodiment of the invention; the figure 3 a synoptic diagram describing a possible implementation of partitioning between TDMA-type multiple access and NOMA-type multiple access in a method for determining a multiple access mode and scheduling according to an embodiment of the invention: the figure 4 represents an example of partitioning between communication links using TDMA-type multiple access and communication links using NOMA-type multiple access at the end of the second step of a method for determining a multiple access mode and scheduling according to an embodiment of the invention: the figure 5 schematically represents the problem of optimizing the scheduling of communication links in a given application case as an illustration; the figure 6a is an illustration of the partitioning of communication links operated by the method according to the invention in the case of two clusters, each having its own logical channel, considered separately; the figure 6b is an illustration of the partitioning of communication links operated by the method according to the invention in the case of two clusters, each having its own logical channel, considered jointly; the figure 7a provides theoretical average throughput obtained as a function of the number of communication links in a given application case, as an illustration, in order to observe the contribution of the method for determining a multiple access mode and scheduling according to the invention; the figure 7b provides theoretical minimum throughput per link obtained as a function of the number of communication links in a given application case, as an illustration, in order to observe the contribution of the method for determining a multiple access mode and scheduling according to the invention; the figure 8 is an illustration of the partitioning of communication links operated by the method according to the invention in the case of two clusters jointly possessing a single logical channel; the figure 9a provides theoretical average throughput obtained as a function of the number of communication links in a given application case, as an illustration, in order to observe the contribution of the method for determining a multiple access mode and scheduling according to the invention; the figure 9b provides theoretical minimum throughput per link obtained as a function of the number of communication links in a given application case, as an illustration, in order to observe the contribution of the method for determining a multiple access mode and scheduling according to the invention; the figure 10 is a synoptic diagram of the steps of a process for determining a multiple access mode and scheduling according to the invention implemented by a decision node.

[0022] Identical references may be used in different figures when they refer to identical or comparable elements. Description détaillée :

[0023] There figure 1 represents an ad hoc network in which a method for determining a network access mode and scheduling according to the invention can be implemented.

[0024] It comprises a plurality of nodes 101, 102, 103, 104, etc. These nodes belong to the same subgroup of nodes, or cluster 110. The ad hoc network can comprise one or more clusters. Some nodes belonging to the same cluster implement communication links represented in the figure 1 in solid lines, such as, for example, communication link 121 between node 101 and node 102. In the example of the figure 1 , N Five communication links are established between ten nodes of cluster 110. A link is defined i as being associated with a Tx transmitter-receiver pair i< - Rx i< We call s i the symbol that the transmitter Tx i< wishes to transmit to the receiver Rx i< The links communicate on the same logical channel, which can create interference at the receiver when they transmit simultaneously, as in the case of NOMA multiple access. The interfering signals for the receivers are represented by dashed lines on the diagram. figure 1 For example, signal 122 represents the interference generated at receiver 102 by emissions from transmitter 104.

[0025] The method according to the invention is applicable in a context where network nodes can communicate using a TDMA or NOMA type multiple access mode. The method can be implemented regardless of the communication standard used to implement TDMA or NOMA transmission. Indeed, the operating point, in terms of data rate, may vary depending on the communication standard used, but this does not affect the overall operation of the method for determining a multiple access mode and scheduling according to the invention.

[0026] For illustrative purposes only, the following description relies on a very simple NOMA multiple access technique, which can be implemented at low cost and without increasing complexity in most existing radios. This NOMA technique is based on the use of linear codes and consists of: to the broadcast: to multiply the symbol s i to transmit by precoding coefficients, at reception: to multiply the received precoded symbols by decoding coefficients, before demodulating them by a conventional demodulator.

[0027] The description considers SISO transmissions (English acronym for Single Input Single Output, or single input single output), where the transmitting and receiving nodes have only one antenna each, but the invention also works when the transmitter and / or receiver has multiple antennas and implements antenna processing techniques.

[0028] By applying the NOMA multiple access technique described above in SISO to all network links, and by setting v j ∈ ℝ 1 × r the linear precoder of the transmitter Tx j< and r ∈ ℕ ∗ the length of the encoders, the signal sent by each transmitter Tx j< is v j T s j , and the signal received at Rx i< can be written as: y i = v i T P i h ii s i + ∑ j = 1 j ≠ i N v j T P i h ij + s j + n i Or P i is the power emitted in Tx i< , h ij is a realization of the complex random attenuation propagation channel, which corresponds to both large-scale fading and small-scale fading of the Tx link j< to Rx i< , and where n i ∈ ℂ r × 1 represents the power noise vector P n .

[0029] After application of the linear decoder of the receiver Rx i< , noted u i ∈ ℝ 1 × r The symbol ŝ i estimated in Rx i< can be written as: s ^ i = u i y i which can be reformulated as: s ^ i = u i v i T P i h ii s i + ∑ j = 1 j ≠ i N u i v j T P j h ij s j + u i n i .

[0030] The powers P i emitted are specific to the devices used as nodes in the network, and are known.

[0031] There figure 2 is a synoptic diagram of a method for determining a multiple access mode and scheduling according to an embodiment of the invention.

[0032] It applies to the case of communication links established between nodes of one or more clusters belonging to an ad hoc network. In the examples presented later, the communication links are operated between nodes belonging to the same cluster (intra-cluster communications), but the process applies identically to communications carried out between nodes belonging to distinct clusters (inter-cluster communications), provided that the nodes are configured to communicate on one or more common transmission channels, or logical channels.

[0033] The method for determining a multiple access mode and scheduling according to the invention comprises a first step 201 of transmitting information relating to the quality of the communication links to a node designated as the decision node for the cluster or for a plurality of clusters. This step is implemented by nodes receiving the communication links and can be performed continuously or at each iteration of the method.

[0034] This step implies identifying a node as the decision-making node. For example, when the process is applied to a single cluster, such as on the figure 1 The decision-making node can be the cluster leader node (in English). cluster head ) ,This is typically determined in ad hoc communication networks to distribute resources among the nodes of a cluster. It can also be one of the nodes involved in the communication links, or another node belonging to the cluster, such as node 105.

[0035] When the process is applied to a plurality of clusters, the decision node can be a separate node for each cluster when the process is implemented separately on the different clusters, or be a common decision node for the plurality of clusters when they are considered jointly.

[0036] The decision node can be chosen based on performance or geometric considerations, and / or elected by the nodes of the cluster. The node designated as the decision node may change dynamically over time.

[0037] According to one embodiment of the invention, information relating to the quality of communication links consists of power levels received by the Rx receiving nodes i< communication links, including the power level of the associated transmission node Tx i< but also the power levels of the signals received from other transmitters on the interfering links and the noise power level perceived at the Rx receiving nodes i< .

[0038] Advantageously, in order to reduce the amount of signaling information transmitted in the cluster, the transmitted power levels can be averaged and transmitted periodically or on demand from the decision-making node.

[0039] According to another embodiment of the invention, the information relating to the quality of the communication links is instantaneous estimation, made by the Rx nodes i< receiving communication links, instantaneous propagation channel h ii on the communication link that concerns them, but also on the instantaneous propagation channel on interfering links h ij such as the interfering link 122 for node 102, and the noise power level at the Rx receiving nodes i< These estimates can, for example, be made from known sequences present in the physical layer for the purpose of estimating the propagation channel.

[0040] According to a preferred embodiment of the invention, the information relating to the quality of the communication links is, for each communication link, statistics associated with the propagation channel of interest. h ii and to interfering propagation channels h ij and the perceived noise power level at the Rx receiving node i< .

[0041] Such statistical estimates of the propagation channel are known to those skilled in the art. For example, in the case of a flat Rayleigh channel, it is possible to estimate the statistical parameters of the channel by taking the empirical variance of the estimated samples of h ij and removing the variance from the noise. For the Rice channel, a method for estimating the statistical parameters: An estimation of the Ricean K-factor from noisy propagation channel samples is proposed in the article by X. Leturc, P. Ciblat and CJ Le Martret, "Estimation of the Ricean K-factor from noisy complex channel coefficients" 2016 50th Asilomar Conference on Signals, Systems and Computers, 2016, pp. 1092-1096, and an estimation of the Ricean K-factor from noisy samples under Nakagami-m masking is proposed in X. Leturc et al., "Estimation of the Ricean K Factor in the Presence of Shadowing" in IEEE Communications Letters, vol. 24, no. 1, pp. 108-112, Jan. 2020.

[0042] In the case where the estimation is done from SINR samples (English acronym for Signal over Interference plus Noise Ratio), a method for estimating the channel statistics in a flat Rayleigh channel with an interfering signal is proposed in the article by D. Jia, X. Leturc, M. Assaad and CL Martret, "Rayleigh Channel Statistics Estimation Using SINR Samples Under Single Interference" 2022 IEEE 95th Vehicular Technology Conference: (VTC2022-Spring), 2022, pp. 1-5.

[0043] Compared to other implementations, transmitting information about the quality of communication links in the form of statistics associated with propagation channels has the advantage of limiting the signaling transmitted over the network and of not being affected by isolated events. Furthermore, using the instantaneous channel can be inefficient when the transmission of information is too slow relative to the temporal fluctuation of the propagation channel: the information received by the decision-making node is then no longer representative of the current propagation channel and therefore does not allow for appropriate decision-making.

[0044] The method for determining a multiple access mode and scheduling according to the invention includes a second step 202, implemented by the decision node, of partitioning the communication links between communication links using NOMA-type multiple access and communication links using TDMA-type multiple access. This partitioning is based on a throughput criterion, the throughputs being calculated from information relating to the quality of the communication links transmitted to the decision node during the first step.

[0045] This second step requires calculating the user throughput available based on the chosen multiple access and interference.

[0046] The physical flow rate associated with an Rx receiver i< Using a TDMA-type multiple access mode is linked to the definition of the physical layer. One way to calculate this throughput at the receiver is to consider the Shannon capacity: R i φ : = W b log 2 1 + SNR i Or W b is the signal bandwidth and the SNR in Rx i< is expressed as: SNR i : = P i h ii 2 P n .

[0047] The := operator is used to define a mathematical variable, unlike the = operator which is obtained after a mathematical deduction.

[0048] The average physical flow rate at the Rx receiver is defined. i< as follows: R ¯ i φ : = E R i φ , with mathematical expectation.

[0049] The average physical flow rate R ¯ i φ The TDMA value for communication link i can therefore be calculated from the SNR. The SNR can be calculated for each communication link from the power levels (signal power and noise power for each communication link) of the forward propagation channel values ​​or estimates of the forward propagation channel statistics transmitted by the nodes during step 201.

[0050] Other methods are possible to calculate this average physical flow rate R ¯ i φ in TDMA, such as using formulas specific to the waveform under consideration, or by linking the SNR to a theoretical or measured bit or packet error rate.

[0051] When the multiple access mode is NOMA, the transmitters communicate simultaneously, which induces interference. The physical data rate at the receiver Rx i< can then be written as: R NOMA , i φ U V : = W b log 2 1 + SINR i U V where the SINR at the Rx receiving node i< depends on the NOMA method used, and U : = u 1 ⋮ u N , V : = v 1 ⋮ v N are respectively the matrices containing all the decoders and precoders obtained by considering that all links in the network use a NOMA access technique.

[0052] In the case given here as an illustration, with SISO nodes using a NOMA-type multiple access technique with linear pre-encoders v j ∈ ℝ 1 × r size r ≤ N for the Tx transmitter j< and linear decoders u i ∈ ℝ 1 × r for the Rx receiver i< , SINR in Rx i< is expressed as follows: SINR i U V = P i h ii 2 u i v i T 2 P n + ∑ j = 1 N P i j ≠ i h ij 2 u i v j T 2 .

[0053] This SINR can be calculated from instantaneous estimates or statistical models of the direct and interfering propagation channels transmitted by the nodes during step 201. It can also be calculated using the power levels emitted by the transmitter of interest and the interfering transmitters during step 201, considering that the received power for a link (direct or interfering) is P i | h ii | 2< or P j | h ij | 2< . The definition of SINR is specific to the NOMA scheme considered. For example, in the case of a power NOMA where interference is handled by a SIC algorithm, the SNR formula does not include the vectors u And v.

[0054] The average physical flow rate at the Rx receiver is defined. i< as follows: R ¯ NOMA , i φ U V : = E R NOMA , i φ U V

[0055] The physical throughput for a communication link using a NOMA-type access mode can therefore be calculated from the information received during step 201.

[0056] User throughput is the throughput related to the protocol layer and is equal to the physical throughput multiplied by the proportion of time allocated to the corresponding link during a transmission. To define it, we consider a frame containing L slots, which we will subsequently call a "frame of length L". L The term "slot" is defined as a sub-time interval of the frame of length L and constitutes the smallest unit of time that can be allocated for communications over a given link. Each frame comprises L slots.

[0057] In the case of a TDMA-type multiple access mode, we then define n i such as the number of transmissions for each link i ∈ {1, ..., N} of the network, where the elementary duration of a transmission is one slot. We assume that L ≥ N so that each link can be allocated at least one transmission. In TDMA, the user throughput at the receiver Rx i< on a length L It can therefore be written as follows: R ¯ TDMA , i u : = n i L R ¯ i φ .

[0058] Furthermore, within the framework of a TDMA access mode, we consider a scheme using a round-robin algorithm, the objective of which is to allocate the same number of slots to each link. To achieve this, the transmitters communicate with each slot one after the other, i.e., Tx 1 < , then Tx 2 < , and so on. This method is subsequently referred to as "round-robin TDMA." Other methods could be considered in a similar manner.

[0059] When TDMA round-robin is applied to a long frame, that is, when L is large compared to N,We can approximate that the number of slots allocated is the same for each link, which can be written as: n 1 = , … , = n N = L N .

[0060] Therefore, the average user throughput at the Rx receiver i< Using round-robin TDMA, it can be written as: R ¯ RRTDMA , i u : = R ¯ i φ N .

[0061] In the case of multiple access of type NOMA, we define n NOMA is equal to the number of times a NOMA-type multiple access is applied to a frame of length L. In NOMA, the user throughput at the Rx receiver i< on a length L It can therefore be written as follows: R ¯ NOMA , i u U V : = n NOMA L R ¯ NOMA , i φ U V .

[0062] As with TDMA-type multiple access, the use of NOMA-type multiple access for the N Communication links can use the following approximation for long frames, that is L large compared to r, r being the length of the NOMA linear encoders when the NOMA access mode uses linear codes: n NOMA ≈ L r ,

[0063] This leads to the expression of the user throughput in Rx i< as follows: R ¯ NOMA , i u U V ≈ R ¯ NOMA , i φ U V r .

[0064] This formula is linked to the NOMA scheme under consideration. For example, a NOMA scheme in the power domain corresponds to r = 1.

[0065] The partitioning of the links into two groups, those using NOMA multiple access and those using TDMA multiple access, is then performed iteratively based on a throughput criterion, in order to favor the solution that provides the highest throughput for each communication link. To do this, we define T N such as the set of links having a higher throughput when using NOMA multiple access than when using TDMA multiple access. Then, we define T d such as the set of links having a higher throughput when using TDMA multiple access than when using NOMA multiple access. The sets T N And T d are calculated so that they form a partition of the set of all links {1, ..., N}, that is to say that T N ∪ T d = {1,..., N} And T N ∩ T d = Ø.

[0066] There figure 3 is a synoptic diagram describing a possible implementation of this step 202 of partitioning communication links in sets T N And T d . It comprises three stages: a first step 301 of calculating user throughput obtained by applying a "round-robin" criterion for TDMA access to all communication links, calculating the throughputs R ¯ RRTDMA , i u for all communication links i; a second step 302 of calculating the user throughput obtained by applying a NOMA-type multiple access to all communication links over an elementary duration for a NOMA transmission, corresponding to r slots. These throughputs depend on the NOMA access technique used and the number of links transmitting simultaneously. In the case given as an illustration, they are obtained by also considering the matrices U ( r ), V ( r ) and the length r , by calculating the flow rates R ¯ NOMA , i u U r , V r for all communication links i ; a third step 303 of determining the sets of links T N And T d defined as the sets of nodes assigned respectively to a NOMA and TDMA type multiple access, based on a throughput criterion, with: T N : = i ∈ 1 , … , N R ¯ NOMA , i u > R ¯ RRTDMA , i u T d : = i ∈ 1 , … , N R ¯ NOMA , i u ≤ R ¯ RRTDMA , i u Or R ¯ NOMA , i u is a simplification of the notation R ¯ NOMA , i u U r , V r ; a fourth step 304 of calculating the user throughput obtained by applying NOMA access to the communication links of the whole T N , that is to say, by recalculating R ¯ NOMA , i u U r , V r for all i ∈ T N . The resulting flow rate is then noted R ¯ NOMA , i u , T N ; a fifth step 305 of determining the communication links belonging to the set T N for which R ¯ NOMA , i u , T N ≤ R ¯ RRTDMA , i u , and the transfer of said communication links of the whole T N towards the whole T d .

[0067] The fourth step 304 and the fifth step 305 of the process are iterated until the sets T N And T d convergent. It can be shown that this algorithm converges since the limiting case reduces to the case where the set T N has only one link, and the whole T d owns N - 1. This situation is equivalent to using TDMA-type multiple access on all network links.

[0068] The implementation presented at the figure 3 has the advantage that the rates used to determine the distribution of multiple accesses of communication links are adjusted as closely as possible to the rate accessible in NOMA.

[0069] Advantageously, in the case where the NOMA scheme under consideration is a scheme using linear precoders / decoders, the vectors and sizes of these linear precoders / decoders can be optimized with respect to the number N of communication links and user data rates during the second step 302 and the fourth step 304 of the process. In this case, at each of these steps, the length r of the linear pre-encoders / decoders and the vectors U ( r ) And V ( r ) can be recalculated to obtain optimal values r *, U* And V* before calculating NOMA flow rates R ¯ NOMA , i u U * r * , V * r * used during the third step 303 and the fifth step 305.

[0070] Indeed, in the case of NOMA-type multiple access where the non-orthogonal access technique is based on the use of linear encoders, the size r of the encoders is between 2 and N - 1 slot, (the case r = N (which amounts to doing TDMA).

[0071] The problem of joint optimization of linear encoders and their size can be written using the approximation of R ¯ NOMA , i u U V , described above, as follows: U * , V * , r * = argmax U , V ∈ ℝ N × r , r ∈ 2 , … , N − 1 ∑ i = 1 N R ¯ NOMA , i φ U V , where the argmax() function gives the index of the maximum.

[0072] One possible method to solve this problem is to process it sequentially for a value r fixed, by solving for any value r = 2 , ...,N - 1. The following problem: U * r , V * r = argmax U , V ∈ ℝ N × r ∑ i = 1 N R ¯ NOMA , i φ U V Or U *( r ), V *( r ) are the optimal linear encoders among linear encoders of sizer .

[0073] The total average user throughput of the network is then calculated using optimal encoders. U* And V* for this value r given, which is expressed as: R ¯ NOMA sum r = ∑ i = 1 N R ¯ NOMA , i φ U * r , V * r

[0074] Finally, we choose the value r * which maximizes the total flow rate, in other words: r * = argmax r = 2 , … , N − 1 R ¯ NOMA sum r

[0075] The linear encoders used are those that have been calculated for r = r* , either U *( r *), V *( r *).

[0076] Note that to solve the problem of calculating U *( r ), V *( r For a given r, it is also possible to use non-convex optimization techniques such as alternating optimization, geometric programming, or Riemannian optimization. The term R ¯ NOMA , i φ does not depend on the instantaneous channel and can be calculated, for example, analytically.

[0077] One possible method, when considering a Rayleigh channel, is to use the following approximation: R ¯ NOMA , i φ ≈ log 2 1 + SINR i hard Or SINR i hard is an approximation of SINR i expressing themselves as: SINR i hard = P i γ ii u i v i T 2 P n + ∑ j = 1 j ≠ i N P j γ ij u i v j T 2

[0078] The solution can be achieved by combining an alternating optimization method and gradient descent for a given encoder length. r , such as : U ∗ r , V ∗ r = argmax U , V ∈ ℝ N × r ∑ i = 1 N log 2 1 + SINR i hard U r , V r .

[0079] There figure 4 represents an example of partitioning between communication links using TDMA-type multiple access and communication links using NOMA-type multiple access at the end of the second step (202) of a method for determining a multiple access mode and scheduling according to an embodiment of the invention. It shows that certain communication links, belonging to the set T d , are associated with the TDMA 402 multi-access mode, while the other communication links, belonging to the set T N , are associated with the NOMA 401 multiple access mode.

[0080] The method according to the invention includes a third step 203 of determining a temporal scheduling of the communication links, respecting the multiple access types calculated during the second step 202. This step is implemented by the decision node. It consists of finding the best time slots to allocate to the communication links on the logical channels assigned to them.

[0081] Always considering a frame of length L The goal is to optimize the number of slots allocated to each link, taking into account the length of the L frame, in order to maximize the overall average network throughput while guaranteeing a minimum throughput for each link in the network. This task can be implemented in two ways: considering that the frame has a length L given and fixed; by jointly optimizing the length L of the frame and the overall average network throughput.

[0082] There figure 5 schematically represents the problem of optimizing the scheduling of communication links in the case of a 501 frame of length L = 10 slots, with N = 6 communication links. Communication links 1, 2, and 3 (502) use a NOMA-type multiple access mode, a NOMA implementation here having a duration of r = 2 slots. One or more pairs of slots must then be reserved in the frame for simultaneous transmissions made by these three communication nodes. Communication links 4 (503), 5 (504), and 6 (505) use a TDMA-type multiple access mode. At least one slot must be reserved in the frame for each of these communication links. Therefore, we have T N = {1, 2, 3} and T d = {4, 5, 6}. The problem consists of allocating slots as efficiently as possible based on a minimum throughput per link, in order to optimize the overall network throughput. The frame definitions remain valid until a new iteration of the process modifies the slot allocations.

[0083] In the case of a frame of length L fixed, the settings n k For k ∈ T d And n NOMA needs to be optimized. n k corresponding to the number of transmissions for the communication link k ∈ T d within the framework, and n NOMA corresponds to the number of times a NOMA access is reserved in the frame. Since L corresponds to the total number of slots to allocate, the parameters n k And n NOMA are constrained by the following equality: ∑ k ∈ T d n k + n NOMA r = L where r is the duration of a NOMA realization. Furthermore, the overall average flow rate R ¯ sum hy the network obtained following the second step 202 of implementing the process according to the invention can be written as follows: R ¯ sum hy : = ∑ j ∈ T N R ¯ NOMA , j u , T N + ∑ k ∈ T d R ¯ TDMA , k u

[0084] Since the technical solution aims to maximize the overall network throughput while ensuring a minimum throughput per link, the scheduling optimization problem (P1) can be formulated as follows: n k ∗ k ∈ T d , n NOMA ∗ = argmax n k k ∈ T d , n NOMA ∈ ℕ ∗ R ¯ sum hy subject to the following constraints: R ¯ TDMA , k u ≥ R 0 u , ∀ k ∈ T d R ¯ NOMA , min u , T N ≥ R 0 u ∑ k ∈ T d n k + n NOMA r = L , where R# is the minimum throughput constraint per link, configurable according to user needs and the feasibility of the problem, R ¯ NOMA , min u , T N : = n NOMA L R ¯ NOMA , min φ And R ¯ NOMA , min φ : = min j ∈ T N R ¯ NOMA , j φ .

[0085] This problem can, for example, be solved using an analytical approach that allows: to test the feasibility analytically, that is without using any iterative procedure, to find the optimal solution of (P1) analytically, that is without using any iterative procedure, which is significantly less complex than the heuristics proposed in the state of the art.

[0086] To test the feasibility of the optimization problem, we can demonstrate that (P1) is feasible if and only if the following condition is met: ∑ k ∈ T d n k min + n NOMA min r ≤ L Or n k min : = LR 0 u R k φ , ∀ k ∈ T d , And n NOMA min : = LR 0 u R ¯ NOMA , min φ are respectively the minimum number of transmissions of the link k and links in T N such that (P1) is feasible, the operator ┌ ┐ denoting the upper integer part.

[0087] This result is demonstrated by showing that the minimum number of transmissions for each communication link ( n k min And n NOMA min The amount needed to meet the throughput constraint must not exceed the total number of slots. L Furthermore, it is interesting to note that the feasibility of (P1) can be verified solely through the condition described above, rather than through an iterative procedure.

[0088] To express the optimal solution of (P1), we define the following variables: R ¯ sum , T N φ : = ∑ j ∈ T N R ¯ NOMA , j φ which corresponds to the total physical throughput of the links in the set T N , k max : = argmax k ∈ T d R ¯ k φ which corresponds to the link with the highest physical bandwidth in T d , n k max the number of slots associated with the link k max and L res : = L − ∑ k ∈ T d n k min − n NOMA min r which corresponds to the number of slots remaining after allocating slots to communication links to guarantee the feasibility of (P1), that is, to respect the constraints of (P1).

[0089] The optimal solution of (P1), which is free from the TDMA round-robin rules, can be expressed as follows: if R ¯ sum , T N φ ≤ r R ¯ k max φ The optimal solution for (P1) is: n k ∗ = n k min , ∀ k ∈ T d \ k max n NOMA ∗ = n NOMA min n k max ∗ = n k max min + L res if R ¯ sum , T N φ > r R ¯ k max φ The optimal solution for (P1) is: n k ∗ = n k min , ∀ k ∈ T d \ k max n NOMA ∗ = n NOMA min + L res r n k max ∗ = n k max min + L res − L res r r T d \ { k max } designating the set T d deprived of k max , and the operator └ ┘ denoting the lower integer part.

[0090] This result can be demonstrated by noting that the optimal allocation of transmissions ( n k ) k ∈ T d And n NOMA is initially carried out by allocating the necessary slots to guarantee the feasibility of (P1), that is to say by allocating n k min slots for communication links k E T d And n NOMA min r slots for the communication links of the whole T N . Secondly, the L res the remaining slots are either allocated to the links of the set T d , or to the links of the whole T N , depending on the condition R ¯ sum , T N φ ≶ r R ¯ k max φ , which indicates the group of links ( T N Or T d ) giving the highest throughput on r slots. If R ¯ sum , T N φ ≤ r R ¯ k max φ , the links of T d provide higher throughput than those of T N and the L res the remaining slots are allocated to k max . If R ¯ sum , T N φ > r R ¯ k max φ , the links of T N provide higher throughput than those of T d and the L res remaining slots are allocated for multiple accesses of type NOMA, then if there are any slots remaining (this number is necessarily less than r ), they are allocated to the link k max .

[0091] Another solution to this problem, compatible with the round-robin algorithm, is to: determine the value of n k min maximum among the nodes of the set of nodes belonging to the set T d ( k ∈ T d ) , either n RR min : = max k ∈ T d n k min , then allocate successively n RR min slots at each link of the set T d . to verify the feasibility of the solution, that is to say to verify that there are enough slots to allocate in round-robin while ensuring a minimum throughput, i.e. the following condition: Mn RR min + n NOMA min r ≤ L , where M is the number of links in the set T d If feasibility is assured, allocate the remaining slots to NOMA links, i.e. n NOMA ∗ = n NOMA min + L res r with L res : = L − Mn RR min − n NOMA min r , relax the constraints, or deviate slightly from the round-robin principle by allocating a different and lesser number of slots n RR min to certain links in the set T d .

[0092] Another solution is to simultaneously optimize the ordering of the nodes and the length L of the frame. Indeed, like the frame length LThis parameter influences the overall average network throughput and can be optimized to improve it. Furthermore, minimizing the frame length (L) reduces network latency.

[0093] As before, an analytical approach can be used to determine a feasibility condition for the problem and the optimal solution. The corresponding optimization problem (P2) can be formulated as follows: n k ∗ k ∈ T d , n NOMA ∗ , L * = argmax n k k ∈ T d , n NOMA , L ∈ ℕ * R ¯ sum hy subject to the following constraints: R ¯ TDMA , k u ≥ R 0 u , ∀ k ∈ T d R ¯ NOMA , min u , T N ≥ R 0 u ∑ k ∈ T d n k + n NOMA r = L .

[0094] To test the feasibility of (P2), it is possible to demonstrate that (P2) is feasible if and only if one of the following conditions is met: R 0 u ∑ k ∈ T d 1 R ¯ k φ + r R ¯ NOMA , min φ < 1 R 0 u ∑ k ∈ T d 1 R ¯ k φ + r R ¯ NOMA , min φ = 1 And R ¯ k φ k ∈ T d , R ¯ NOMA , min φ are rational numbers.

[0095] The rationality of average data rates is mostly respected since we are considering digital communications.

[0096] To express the optimal solution of (P2), we define the following operators: the GCD (greatest common divisor) and the LCM (least common multiple). These two operators can be calculated using Euclid's algorithm. Furthermore, in what follows, the operation LCM(( a n ) n ∈ M , b ) corresponds to the LCM of all the terms of a n , n ∈ M and b .

[0097] The optimal solution to (P2) can be obtained using the following procedure: Test the feasibility of (P2) using the feasibility condition defined above. This step involves analyzing whether the stated conditions are achievable to guarantee a minimum throughput per link; that is, whether the number of slots to be allocated in the frame of length L is sufficient for each link to have a user throughput greater than the minimum user throughput. R 0 u imposed. If this is not the case, the minimum flow rate constraint must be reduced, or the transmission power of the devices increased; calculate R ¯ sum , T N φ : = ∑ j ∈ T i R ¯ NOMA , j φ And k max : = argmax k ∈ T d R ¯ k φ then compare R ¯ sum , T N φ And r R ¯ k max φ , if R ¯ sum , T N φ ≤ r R ¯ k max φ , ∘ calculate the values p k q k ∈ ℕ ∗ 2 And p NOMA q NOMA ∈ ℕ ∗ 2 such as: ∀ k ∈ T d \ K max , p k q k = R 0 u R ¯ k φ p NOMA q NOMA = R 0 u R ¯ NOMA , min φ Or K max = k R ¯ k φ = R ¯ k max φ , GCD(p NOMA , q NOMA ) = 1 and ∀k ∈ T d \ , gcd(pk , qk ) = 1 ; to calculate L* = LCM( , q NOMA). if R ¯ sum , T N φ > r R ¯ k max φ , to calculate the values p k , q k ∈ ℕ ∗ 2 And p 0 , q 0 ∈ ℕ ∗ 2 such as: ∀ k ∈ T d , p k q k = R 0 u R ¯ k φ p 0 q 0 = 1 r 1 − ∑ k ∈ T d R 0 u R ¯ k φ where GCD(p 0 , q 0 ) = 1 and Vk ∈ T d , GCD(pk, qk) = 1; calculate L* = LCM(( q k ) k ∈ T d , q 0) ; calculate the parameters n k ∗ k ∈ T d And n NOMA ∗ by solving problem (P1) over a frame length L*.

[0098] Finally, the method of determining a multiple access mode and scheduling according to the invention includes a fourth step (204), carried out by the decision-making node, of transmitting information concerning the multiple access modes to be used for the communication links and their temporal scheduling, at a minimum to the nodes involved in the communication links.

[0099] The method for determining a multiple access mode and scheduling according to the invention is divided into two main phases based on a throughput criterion: the partitioning of communication links between links using a TDMA type multiple access mode and links using a NOMA type multiple access mode, carried out during the second step 202 using an iterative algorithm, and the optimization of the scheduling of communication links, carried out during the third step 203, can be solved optimally and with very little complexity.

[0100] The method according to the invention can be implemented within a cluster in an ad hoc network. All nodes communicate on the same logical channel, and the second, third, and fourth steps of the method according to the invention are implemented by a dynamically elected decision node. Implementing the method within the cluster improves the overall average throughput within the cluster, while guaranteeing a minimum throughput per communication link.

[0101] Within an ad hoc network of Kclusters, each cluster being named C k and containing n Ck links, the process can be implemented on a grouping of p clusters, with 2 ≤ p ≤ K.

[0102] Several application scenarios are possible. Initially, we assume that the spectral resource is sufficient, meaning that the cluster grouping has access to p separate logical channels. In this case, it is possible to allocate a logical channel to each cluster and apply the method of determining a multiple access mode and scheduling according to the invention to each of the clusters independently. For example, for p = 2 named clusters C 1 and C 2, the links of C 1 are assigned the logic channel f 1 and the decision-making node of C 1 applies the method according to the invention. Similarly, the links of C2 communicate on the second logical channel f 2 and the decision-making node of C 2 applies the method according to the invention independently of C 1.

[0103] There figure 6a is an illustration of the partitioning of communication links operated by the method according to the invention in this first case of application on p = 2 clusters, the cluster C 1601 and the cluster C 2602. Each cluster comprises six nodes and three communication links. Following the implementation of the process, the nodes of the cluster C 1. Devices in zone 611 use NOMA multiple access mode, and those in zone 612 use TDMA multiple access mode on the logical channel f 1. Similarly, the cluster nodes C 2 devices in zone 613 use NOMA multiple access mode, and those in zone 614 use TDMA multiple access mode on the logical channelf 2.

[0104] According to another embodiment, the problem is analyzed globally for the grouping of p clusters. As an example, let's consider an application case with p = 2 clusters associated respectively with a logical channel f 1 and f 2. In this case, resources can be grouped between the two clusters, the logical channel f 1 that can be allocated to certain links of the p clusters of the grouping, and the second logical channel f 2 that can be allocated to other links. It is therefore a matter of jointly optimizing the NOMA / TDMA access mode, the allocation of logical channels and the link scheduling.

[0105] To this end, the method according to the invention can be implemented in the following way: A common decision node for the p grouped clusters is elected. Information regarding the quality of direct and interfering communication links, for example, statistics related to propagation channels, is sent back to the decision node by the cluster nodes, either directly or via intermediate nodes. Interfering links include links between distinct cluster nodes. Based on this information, the decision node implements the method for determining a multiple access mode and scheduling according to the invention, extended to the joint management of all logical channels and accesses, namely, in particular: ∘ the implementation of the second step 202 of the method on the links of the two clusters jointly, in order to partition them between a set T d of links operated with a TDMA-type multiple access mode and a set T N of links operated with a NOMA-type multiple access mode. This step is performed assuming that all links communicate on the same logical channel. Data rates can be calculated either by considering the bandwidth of a single logical channel or the bandwidth of all logical channels, or by allocating a portion of the logical channels (for example, the channel f 1) to the links of T N using NOMA-type multiple access, ∘ the allocation of the other part of the logical channels (for example the channel f 2) to the links of T d using TDMA access, the decision-making node sends the calculated parameters to the corresponding nodes in the network.

[0106] Similarly, each cluster can elect a decision-making node for its own cluster, and then the decision-making nodes elect a common decision-making node for the group of clusters. The nodes transmit information about the quality of communication links to their cluster's decision-making node, which then forwards it to the common decision-making node. This solution helps limit inter-cluster transmissions.

[0107] There figure 6b is an illustration of this second application of the process on a group of p = 2 clusters, the cluster C 1601 and the cluster C 2,602, each associated with a logical channel f 1 and f2. Each cluster comprises six nodes and three communication links. Following the implementation of the process, which here considers interference related to emissions from nodes belonging to different clusters, the nodes within area 621 use a NOMA-type multiple access mode on the logical channel f 1, and those in zone 622 use a TDMA-type multiple access mode on the logical channel f 2.

[0108] Compared to the previous embodiment, the joint management solution for NOMA / TDMA access and logical channels offers better overall throughput than a solution where the process is applied to each cluster independently.

[0109] There figure 7a gives the average theoretical throughput obtained in the network as a function of the number of communication links, in order to quantify the contribution of the process according to the invention in an application case where the network comprises p = 2 clusters and two logical channels f1 and f 2. This is a theoretical overall throughput (sum of the throughputs of all links) obtained by considering a logical channel of bandwidth W b equal to 1 MHz. Curve 701 represents the performance obtained by implementing a TDMA-type multiple access technique independently on all communication links of each cluster, using a logical channel specific to the cluster. Curve 702 represents the same application case using a NOMA-type multiple access technique. It can be observed that the use of NOMA allows for better average throughput than TDMA as the number of communication links increases. Curve 703 represents the performance obtained by implementing the method according to the invention independently on each of the clusters. It can be observed that the implementation of the method according to the invention considerably improves throughput compared to solutions based on the use of TDMA or NOMA. Finally, curve 704 represents the performance obtained by implementing the method according to the invention on the grouping of the p clusters.We observe that the average throughput is even better, particularly when the number of communication links increases.

[0110] There figure 7b illustrates the minimum theoretical bandwidth available per link, in the same application case as the figure 7a Curve 711 corresponds to the application case of curve 701, and respectively for curves (712, 702), (713, 703), and (714, 704). It is observed that the minimum available throughput in the case of NOMA multiple access mode collapses as the number of available links increases, and that this minimum throughput is very good when the multiple access mode is TDMA. The proposed solution is less efficient than TDMA in terms of minimum throughput, but guarantees a minimum throughput, unlike the NOMA solution. The performance obtained by implementing the method according to the invention is comparable whether the clusters are grouped or not.

[0111] Another application is where spatial reuse of logical channels is insufficient to guarantee orthogonality between the communication links of different clusters; that is, the number of logical channels is less than the number of clusters. This can be the case, for example, with spatial reuse of transmission channels, which allows the network to operate with fewer logical channels than clusters, provided the network topology allows the same channels to be reused in sufficiently distant clusters. Spatial reuse may prove insufficient when clusters are too close to each other. In this case, one possible solution is to implement TDMA multiplexing between the clusters. However, this solution has the drawback of dividing by p the average flow rate.

[0112] Another solution is to implement the method of determining a multiple access mode and scheduling according to the invention on a grouping of clusters and logical channels, as illustrated previously, even when the number of logical channels is less than the number of clusters.

[0113] There figure 8 is an illustration of this application of the process to a group of p = 2 clusters, the cluster C 1801 and the cluster C 2802, both associated with the same logical channel f 1. Each cluster comprises six nodes and three communication links. Following the implementation of the process, which here considers interference related to emissions from nodes belonging to different clusters, the nodes in area 811 use a NOMA-type multiple access mode and those in area 812 use a TDMA-type multiple access mode, scheduled on the logical channel f 1.

[0114] The advantages of this implementation are that it provides a much better overall theoretical throughput than a solution based on a TDMA type access mode between the nodes of the different clusters, and that it guarantees a minimum throughput, unlike a solution based on a NOMA type access mode where the minimum throughput tends towards zero when the number of communication links increases.

[0115] There figure 9a gives the theoretical average flow rates obtained in order to quantify the contribution of the process according to the invention in an application case where the network includes p = 2 clusters and a single logical channel f1. The graph shows the average theoretical throughput obtained in the network as a function of the number of communication links. Curve 901 represents the performance obtained by implementing a TDMA-type multiple access technique on all communication links of the clusters, distributing the use of the logical channel equally between the two clusters (round-robin). Curve 902 represents the same application case by optimizing the scheduling of resources for the two clusters on the logical channel in order to maximize the overall throughput. Curve 903 represents the same application case using a NOMA-type multiple access technique. It can be observed that the use of NOMA allows for better average throughput than even optimized TDMA, particularly as the number of communication links increases. Curve 904 represents the performance obtained by implementing the method according to the invention on the grouping of the two clusters.It is observed that implementing the method according to the invention significantly improves data rates compared to solutions based on the use of TDMA, whether optimized or not. The performance obtained is comparable to that obtained when all communication links use NOMA-type multiple access.

[0116] There figure 9b illustrates the minimum theoretical bandwidth available per link, in the same application case as the figure 9a Curve 911 corresponds to the application case of curve 901, and respectively for curves (912, 902), (913, 903), and (914, 904). It is observed that the minimum available throughput in the case of NOMA multiple access mode drops sharply as the number of available links increases, whereas it is very good when the multiple access mode is TDMA. The proposed solution is slightly less efficient than the one based on unoptimized TDMA, but it guarantees a minimum throughput, unlike the NOMA-based solution.

[0117] The performances presented at figures 7a, 7b , 9a et 9b are given as illustrations for specific application cases where the number p the number of clusters is equal to two. However, the invention applies in a comparable manner to the grouping of a number of clusters greater than two.

[0118] The invention therefore relates to a method for determining a multiple access and scheduling mode for a plurality of communication links in an ad hoc network, but also to a node in an ad hoc network, comprising computing means such as, for example, a microprocessor, a DSP (Digital Signal Processor). Digital Signal Processor, or digital signal processor), an FPGA (English acronym for Field Programmable Gate Array, or programmable gate network), an ASIC (English acronym for Application-Specific Integrated Circuit, or application-specific integrated circuit), any combination of these means, or any hardware component enabling it to implement the steps of the invention enabling it to play the role of decision-making node responsible for determining the access mode between a NOMA access mode and a TDMA access mode for each of the communication links, and for scheduling these communication links.

[0119] There figure 10 is a synoptic diagram of the steps in a method for determining a multiple access mode and scheduling according to the invention, implemented by a decision node. These steps include a first step (1001) of receiving, from nodes involved in the communication links, information relating to the quality of communication links operated between nodes of the ad hoc network, each communication link being established between nodes belonging to the same cluster, and successive steps 1002, 1003 and 1003 corresponding to the second (202), third (203) and fourth (204) steps of the method according to the invention described in the figure 2 .

Claims

1. Multiple access mode determination and scheduling method for a plurality of communication links in an ad-hoc network comprising a plurality of nodes grouped together into one or more clusters, the communication links being operated on at least one logical channel, the method comprising - a first step (201), implemented by said nodes, of transmitting, to a node designated as decision-making node, information relating to a quality of said communication links, - a second step (202), implemented by said decision-making node, of partitioning said communication links between communication links using NOMA multiple access and communication links using TDMA multiple access, based on a data rate criterion computed on the basis of the information relating to the quality of said communication links transmitted in the first step (201), - a third step (203), implemented by said decision-making node, of determining a temporal scheduling of said communication links on said at least one logical channel, while complying with the types of multiple access computed in the second step, - a fourth step (204), implemented by said decision-making node, of transmitting the partitioning information computed in the second step and the temporal scheduling information computed in the third step to the nodes involved in said communication links.

2. Multiple access mode determination and scheduling method according to Claim 1, wherein the information relating to a quality of the communication links is, for each communication link: - statistical information regarding a propagation channel of said communication link, - statistical information regarding interfering propagation channels, and - a noise power level perceived by the destination node of the communication link.

3. Multiple access mode determination and scheduling method according to either of the preceding claims, wherein the second step (202) of partitioning said communication links comprises implementing an iterative algorithm comprising, for each communication link, computing a user data rate using a TDMA multiple access mode, computing a user data rate using a NOMA multiple access mode taking into account the multiple access modes used by the other communication links, and choosing the access mode that maximizes the user data rate of the communication link.

4. Multiple access mode determination and scheduling method according to one of the preceding claims, wherein the second step (202) of partitioning said communication links comprises: - a step (301) of computing a user data rate for each communication link when all of the communication links are associated with TDMA multiple access, - a step (302) of computing a user data rate for each communication link when all of the communication links are associated with NOMA multiple access, - a step (303) of determining a set TN of communication links associated with NOMA multiple access and a set Td of communication links associated with TDMA multiple access by comparing the respective user data rates for each communication link, - iteratively, until convergence is achieved: ∘ a step (304) of computing a user data rate for each communication link of the set TN when only the communication links of said set TN use NOMA multiple access, ∘ a step (305) of searching for communication links belonging to the set TN for which the user data rate for TDMA multiple access is greater than or equal to the user data rate for NOMA multiple access, and transferring said communication links to the set Td of communication links using TDMA multiple access.

5. Multiple access mode determination and scheduling method according to one of the preceding claims, wherein the NOMA multiple access technique is based on the use of linear encoders / decoders, and in which the second step (202) of partitioning said communication links between communication links using NOMA multiple access and communication links using TDMA multiple access based on a data rate criterion comprises computing a linear encoder / decoder size r and computing encoding / decoding matrices U and V adapted to the number of communication links using NOMA multiple access.

6. Multiple access mode determination and scheduling method according to one of the preceding claims, wherein the third step (203) of partitioning said communication links comprises defining a long time interval, or frame, divided into a plurality L of short time intervals, or slots, and of distributing said L slots between the communication links so as to maximize the average overall data rate of the ad-hoc communication network while at the same time guaranteeing a minimum data rate for each communication link.

7. Multiple access mode determination and scheduling method according to the preceding claim, wherein LR 0 u R k φ slots are assigned exclusively to each communication link using TDMA multiple access, where R 0 u is a minimum data rate constraint per link and R k φ is a physical data rate associated with the communication link, LR 0 u R ¯ NOMA , min φ slots are assigned to the communication links using NOMA multiple access, and in which the remaining slots are distributed between the communication links using NOMA multiple access and the communication link using TDMA multiple access having the highest physical data rate R k φ .

8. Multiple access mode determination and scheduling method according to either of Claims 6 and 7, wherein the third step (203) of partitioning said communication links furthermore comprises computing an optimum frame length L* taking into account the results from the second step (202) of partitioning the communication links.

9. Multiple access mode determination and scheduling method according to one of the preceding claims, implemented jointly on a plurality of clusters.

10. Decision-making node for an ad-hoc network comprising a plurality of nodes grouped together into one or more clusters and implementing a plurality of communication links on at least one logical channel, said decision-making node comprising computing means configured to implement: - a first step (1001) of receiving information relating to a quality of said communication links, - a second step (1002) of partitioning said communication links between communication links using NOMA multiple access and communication links using TDMA multiple access, based on a data rate criterion computed on the basis of the information relating to the quality of said communication links received in the first step (201), - a third step (1003) of determining a temporal scheduling of said communication links on said at least one logical channel, while complying with the types of multiple access computed in the second step, - a fourth step (1004) of transmitting the partitioning information computed in the second step and the temporal scheduling information computed in the third step to the nodes involved in said communication links.

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