DESC:FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See section 10, rule 13)

A METHOD OF DYNAMICALLY ALLOCATING THE TIME SLOTS OF TDMA CHANNEL AMONG THE NODES OF THE MARITIME WIRELESS AD-HOC NETWORK;

BHARAT ELECTRONICS LIMITED
OUTER RING ROAD, NAGAVARA, BANGALORE- 560045,
KARNATAKA, INDIA

THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.

Field of the invention

The present invention mainly relates to a method of allocating a TDMA slots among a node and more particularly to the method of dynamically sharing the time slots of TDMA channel among the nodes of the maritime wireless ad-hoc network based on the knowledge of global network topology.

Background of the invention

Time-division multiple access (TDMA) is well known in the art which is a channel access method for shared-medium networks. It allows several users to share the same frequency channel by dividing the signal into different time slots. The users transmit in rapid succession, one after the other, each using its own time slot. This allows multiple stations to share the same transmission medium (e.g. radio frequency channel) while using only a part of its channel capacity.
Semi mobile ad-hoc network refers to the network in which change in topology occurs once in few seconds only. Maritime ship borne communication, military tank based networks and for home- guard networks are the few examples of tactical semi-mobile ad-hoc networks. Ad- hoc network typically includes number of geographically-distributed, potentially mobile units and nodes can communicate with each other over a wireless media without the support of an infrastructure-based or moderator. One access scheme for ad hoc networks is Time Division Multiple Access (TDMA), in which the transmission resource of a radio frequency is divided into time slots, and a node may transmit in one or several time slots. Sharing of the TDMA slots among the nodes may be fixed or dynamic depending upon the QoS and load of the network. Dynamic slot sharing may be done by the coordinator or without the coordinator. The existing dynamic TDMA slot sharing methods of ad-hoc networking are mainly for urban and may not be successfully used for maritime ad-hoc networking. It is because of the reason that ad-hoc networking at sea involves much larger distance between nodes in contrast to the nodes of the ad-hoc network in urban area or land. Ad-hoc networking at sea is achieved through nodes operating with UHF, VHF, and HF radios. These UHF/VHF/HF radios have pre-defined frequency band usage. This causes interference while other users try to use the pre-defined channel and also has limitation with the available channel capacity.
Another drawback of ad-hoc networking at sea is that the nodes are combined with omni-directional radiation with high power transmission to bridge the long distance, which may lead to reflection from sea surface. This reflection could mislead for channel occupancy states among the neighbour nodes. Hence coordination about the channel usage among the neighbours is essential. The channel conditions experienced by each node in the sea drastically varies among their neighbour nodes as well and hence deciding a reliable radio link with a neighbour node becomes more challenging than urban/land communication. Other drawbacks are the larger propagation delay, uni-directional air interface and bobbling link states with very frequent on/off link state among their direct neighbour nodes.
The prior art discloses the different methods of dynamic slot sharing schemes of a common TDMA channel in wireless ad-hoc network. For example, document US 7082111 titled “Method for dynamically allocating time slots of a common TDMA broadcast channel to a network of transceiver nodes” describes distributed, dynamic TDMA time slot allocation method. It presents a method by which time slots are divided into a plurality of time slot sub-sets, defining for each transceiver node a common function that assigns one time slot sub-set of the plurality of time slot sub-sets to each point in space, where each point in space is identified by a unique set of space coordinates. Common function is a two-dimensional function S (X, Y) that assigns an integer to each point (X, Y) in two-dimensional space. The integer assigned to each point (X, Y) represents one of the time slot sets. A time slot can be uniquely identified by the pair (M, E), where M is the time slots circular sequence number (column number of the two dimensional time slot space ‘S’) and F is the time slots frame sequence number (row number of ‘S’). The sequence number S and the circular sequence number M of a particular time slot are related by modulo function. This method is independent of the instantaneous connectivity between the nodes of the network.
Another, document US20050029347 titled “Slot adaptation in a wireless dynamic TDMA network with reservations” provides slot adaptation method with reservations by measuring the quality of time slots and sharing the slot quality information with neighbours in a wireless dynamic TDMA network. During operation, the system receives a vector from a neighbour node, wherein a respective element in the vector indicates received signal quality for a corresponding time slot in a frame with respect to that neighbour node. Next, the system updates a record which indicates the received signal quality for all the time slots within a frame for the neighbour node based on the received vector. The system then determines a transmission threshold for a time slot with respect to a neighbour node based on the record. The system reserves time slot for future transmissions to the neighbour node if the record indicates that the received signal quality in that time slot is better than the reservation threshold. The goal of the protocol is to give us a statistical basis to make three decisions: should a slot be used for a given neighbour, should a node make a reservation for a slot, and should a node release a reservation for a slot.
Another, document US8942197 titled “Mobile ad-hoc Network with Dynamic slot assignments and related methods” describes the method of sharing the TDMA time slots among the nodes of a mobile ad-hoc network (MANET). The transceiver and the controller nodes of the network is divided into the plurality of first type nodes and second type nodes based on the current topology density in the topologic area relative to a topological density threshold. TDMA epoch includes a beacon interval, an digital voice interval, a contention interval, and a data interval. First type nodes are guaranteed with periodic time slots in each TDMA epoch. Second type nodes communicate in the contention interval of the TDMA epoch. Mobile nodes can be configured dynamically into first or second type nodes depending upon traffic characteristics. First type nodes develop the backbone of the MANET, through which all the information will be routed.
Further, document US 2007/0274320A1 titled “System, methods and apparatus for allocating time slots in an ad-hoc wireless communication network” provides the technique for allocating one or more time slots to transmit a particular data stream along the route based on the QoS requirements to transmit the particular data stream. In this implementation, a Scout Request message (SRM) is sent from the source to the destination to allocate time slots along the route to transmit a particular data stream to the destination. The SRM can include QoS requirements to transmit the particular data stream. Each intermediate node along the route can allocate one or more time slots to transmit the particular data stream based on the QoS requirements needed to transmit the particular data stream along the route.
Further, document US 2013/0089011A1 titled “Cognitive Mobile Time Division Duplex Ad-hoc Network” describes TDD (Time Division Duplexing) and TDMA MAC algorithm that maintains routes to allow delivery of adequate bandwidth for applications by using a routing protocol that has a built in slot reservation algorithm. The routing protocol loosely follows the terminology used in AODV routing proposal. TDMA framing of this disclosure has super frame being divided into two frames time slots, wherein a first frame time slot can operate in a master mode while a second frame time slot can operate in a slave mode. Framing and channelization is added to the AODV routing algorithm. Route request and reply messages have additional fields for frame type and channel information that is used by nodes to allocate TDD frames and to select channels. A node can be master or slave, or be coordinated regarding time slot allocations. A node that is a master coordinates channel access over an area that can be determined based on range of hello messages received or Aloha multiple access protocol.
Furthermore, document US 20004247804A1 titled “Mobile Ad-hoc Network” describes the method for improving the spectral efficiency and scalability of Mobile Ad-Hoc Networking (MANET) system. This MANET nodes are topology aware (checks the active nodes in the network) and cognitive to adjust their behaviour to minimize interference. The whole band is assigned for simultaneous reception and transmission frequencies are determined to use the least possible number of frequencies according to the active population status, transmission requirements and priorities of the nodes. The transceiver scans the frequency usage pattern and chose the RF band accordingly. Relay nodes operate in same frequency and in different time slots. Source and destination nodes can operate in different frequencies which has relay nodes in between them.
Therefore, there is a need in the art with a method of dynamically allocating the time slots of TDMA channel among the nodes of the maritime wireless ad-hoc network and to solve the above mentioned limitations.

Summary of the Invention

An aspect of the present invention is to address at least the above-mentioned problems and/or disadvantages and to provide at least the advantages described below.
According, in one aspect of the present invention relates to a method of dynamically sharing time slots of TDMA channel among nodes of a maritime wireless ad-hoc network, the method comprising: categorizing the time slots of a TDMA channel into a plurality of time slot pools by a slot pooling method, wherein the time slots of the TDMA channel are categorized into static and dynamic slot pools, where the static slot pool is a control pool and the dynamic slot pools are data slot pool, relay pool and high band pool, determining the TDMA slot share of each slot pool based on current active nodes in the network by a ‘x-node configuration’, determining the slot sharing in each slot pool among the nodes of the network by a ‘matrix index method’, selecting a neighbour node among the nodes of the network by an individual node by a ‘fuzzy driven neighbour node selection’ method and selecting a relay neighbour node among the nodes of the network by an individual node by a ‘fuzzy driven relay node selection’ method, where the ‘fuzzy driven relay node selection’ decides relay nodes of the network instantaneously.
Other aspects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses exemplary embodiments of the invention.
Brief description of the drawings

The above and other aspects, features, and advantages of certain exemplary embodiments of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings in which:
Figure 1-A is an illustration of the time slots division of a TDMA super frame with static and dynamic according to one embodiment of the present invention.
Figure 1-B graphically illustrates the slot pool share of the super frame shown in Figure 1-A into 3 slot pools according to one embodiment of the present invention.
Figure 2 illustrates the TDMA indexing for control slot pool of TDMA super frame according to one embodiment of the present invention.
Figure 3-A is a table showing the descriptions of variables used in one exemplary implementation that describes the dynamic time slot allocation process occurring in each node of the network according to one embodiment of the present invention.
Figure 3-B illustrates the data slot matrix for different TDMA configurations of Figure 3-A according to one embodiment of the present invention.
Figure 4-A graphically illustrates the division of data/relay slot portion of Figure 1-B according to one embodiment of the present invention.
Figure 4-B is a table that details the sharing of relay slot of Figure 4-A which is available in each node of the network according to one embodiment of the present invention.
Figure 4-C illustrates the relay slot matrix for different TDMA configurations of Figure 3-A according to one embodiment of the present invention.
Figure 5-A is a table which describes sharing of high band slot of Figure 4-A according to one embodiment of the present invention.
Figure 5-B shows the high band slot matrix for different TDMA configurations of Figure 3-A according to one embodiment of the present invention.
Figure 6 shows a conditions base for optimal neighbour node selection fuzzifier according to one embodiment of the present invention.
Figure 7 shows a conditions base for optimal relay node selection fuzzifier according to one embodiment of the present invention.
Persons skilled in the art will appreciate that elements in the figures are illustrated for simplicity and clarity and may have not been drawn to scale. For example, the dimensions of some of the elements in the figure may be exaggerated relative to other elements to help to improve understanding of various exemplary embodiments of the present disclosure. Throughout the drawings, it should be noted that like reference numbers are used to depict the same or similar elements, features, and structures.
Detailed description of the invention

The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of exemplary embodiments of the invention as defined by the claims and their equivalents. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope and spirit of the invention. In addition, descriptions of well-known functions and constructions are omitted for clarity and conciseness.
The terms and words used in the following description and claims are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the invention. Accordingly, it should be apparent to those skilled in the art that the following description of exemplary embodiments of the present invention are provided for illustration purpose only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.
It is to be understood that the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a component surface” includes reference to one or more of such surfaces.
By the term “substantially” it is meant that the recited characteristic, parameter, or value need not be achieved exactly, but that deviations or variations, including for example, tolerances, measurement error, measurement accuracy limitations and other factors known to those of skill in the art, may occur in amounts that do not preclude the effect the characteristic is intended to provide.
Figs. 1 through 7, discussed below, and the various embodiments used to describe the principles of the present disclosure in this patent document are by way of illustration only and should not be construed in any way that would limit the scope of the disclosure. Those skilled in the art will understand that the principles of the present disclosure may be implemented in any suitably arranged communications system. The terms used to describe various embodiments are exemplary. It should be understood that these are provided to merely aid the understanding of the description, and that their use and definitions, in no way limit the scope of the invention. Terms first, second, and the like are used to differentiate between objects having the same terminology and are in no way intended to represent a chronological order, unless where explicitly stated otherwise. A set is defined as a non-empty set including at least one element.
The present invention relates to a method of dynamically allocating the time slots of TDMA channel among the nodes of the maritime wireless ad-hoc network based on the knowledge of global network topology. Global network topology is derived using optimal relay and neighbour node selection with the metrics applicable for ad-hoc networking at sea. More specifically, the present is related to a method for TDMA slot adaptation with dynamic slot reservations to satisfy the required quality of service (QoS) for information exchange in a semi mobile multi-hop wireless communication network.
The present invention discloses a method of dynamically sharing the TDMA slots based on neighbour strategy of the global network for satisfying the QoS requirements of communication among nodes used for maritime communication. The present invention provides the ‘slot pooling concept’ that divides the TDMA slots into four slot pools: “control pool, data pool, relay pool and high bandwidth pool”. The total TDMA frame duration is divided in the ratio of 10%: 45%: 22.5%: 22.5% respectively for control pool, data pool, relay pool and high bandwidth pool. Every node in the network will get a slot in the control pool. According to the total number of nodes (x-nodes) in the network, slots of the ‘four pools’ will be shared among ‘x’ nodes. Every node that enters the network will get a slot in the control pool. Control pool sharing is determined based on the MAC identity of the nodes. Slots of the ‘data pool’ are designated for the message transmission, voice and emergency transmission. Sharing of slots of data pool is determined by the value of ‘x-node’ configuration. Slots of ‘high bandwidth pool’ are allocated on a priority basis and used for high bandwidth demands such as voice, multimedia and image transmission. Slots of the ‘relay pool’ are shared among the relay nodes. The maximum number of relay nodes which could share the slots of the ‘relay pool’ is decided by the ‘x-node’ configuration.
The present invention relates to a method for dynamic TDMA slot allocation based on global network topology. The TDMA slots are divided into static and dynamic pool, where in slots of the static pool are pre-assigned to authenticated users of the network based on their unique identification numbers. The Static slots are called control slots which enable the collision free node join or leave. The slot pooling mechanism is introduced for dynamic pool that devises the dynamic slots of the TDMA frame into three different slots pools: 1 data pool, 2 relay pool and 3 high band pool. Maximum number of nodes in the current network, topology and the information about how the nodes are connected in the network are obtained by the MANET method. Decision about the network topology and the neighbour node selection is determined through novel fuzzy approach with link metrics exclusive for ad-hoc networking at sea. The novel neighbour selection addresses the concerns of networking at sea by means of accommodating metrics such as propagation delay, bobbling rate, distance, link expiration time, link duration, node position, connectivity to multi-hop nodes, remote node reachability and statistical prediction.
Slots of the ‘data pool’ are shared equally among the active nodes of the network, which is to ensure minimum tactical messaging. Relay slots are shared among relay nodes and used only for relaying the packets. Slot of the ‘high band pool’ are spared for catering the real time high bandwidth communication such as video or multimedia communication among one-hop nodes. There is no need of master or coordinator to decide the slot share and every node is aware its slot-share and also about the slots used by other nodes. Slot share is updated and acknowledged by all nodes in the network, through network control packet exchange method that require only few bytes, which reduces the overheads compared to fully dynamic TDMA. Slots are shared depending upon the QoS and load of the network that has enhanced the bandwidth utilization than conventional TDMA and CSMA.
In one embodiment, the present invention provides the method of sharing the TDMA slots in an ad-hoc manner without the need of any coordinator or master, using the concept of ‘x-node’ configuration and matrix-index method.
According to the ‘x-node’ configuration, wherein the slots of the ‘data pool’ will be shared among ‘x’ nodes of the network that satisfies the equation:

The number of active nodes in the current network topology will be rounded near to ‘x’ such that (n mod x) is zero’ and x= n and ‘x’ can take values such as 2, 4, 6 etc. Slots of the ‘data pool’ will be listed in a matrix format and notated as ‘data slot matrix’. These matrixes will have ‘y’ rows and ‘c1’ columns that satisfy the following equation:
The product of (s, c1) = the total number of slots of data pool
The value of ‘s’ is equal to ‘x’. Each node in the network will pick one row index out of ‘y’ row indexes of the ‘data slot matrix’ based on their MAC address.
Similarly slots of ‘relay pool’ are shared among relay nodes by the following equation:

‘m’ is decided by the topology of the current network.
‘x’ is the value as in ‘x-node configuration’
Slots of the ‘relay pool’ will be listed in a matrix format and notated as ‘relay slot matrix’. These matrixes will have ‘?’ rows and ‘c2’ columns that satisfy the following equation:
product of (?,c2) = total number of slots of relay pool
Value of ‘?’ is equal to ‘r’. Each node that has been assigned as relay node will pick one index out of ‘?’ row indexes of the relay slot map matrix.
According to the concept of matrix index, wherein every node can pick a certain index of this matrix to occupy the TDMA time slots. Picking of slots are defined by the matrix index method.
According to another exemplary embodiment, the present invention provides optimal method for determining the neighbour node and the relay status using fuzzy logic with the link metrics. The link metrics considers the metrics that are applicable for ad-hoc networking at sea. The metrics are: hello packet recognition time, bobbling factor which is defined as the periodicity pattern of loss of ‘hello packet’ of its neighbour, uni-directional link status, link duration which is decided based on the connectivity time between the nodes, link expiration rate and CRC error/packet error rate. Relay node status of the nodes are decided based on the fuzzy logic with the metrics such as: node position, neighbourhood connectivity status and remote node reachability.
According to one embodiment of the invention, new node joining and TDMA slot sharing among the nodes in the wireless maritime Ad-hoc network comprises of five blocks. First block is the TDMA frame synchronization which determines the start and end of the TDMA super frame. Since the nodes involved in maritime communication is having the assurance of obtaining the 1pps clock through GPS systems, TDMA frame boundaries are determined through 1pps signal. TDMA super frame is further sub divided into macro-frames and mini-frames. Duration of the TDMA macro-frame slot and mini-frame (control slot) slot is chosen in a way to accommodate the long propagation time and transmission duration of ad-hoc networking at sea. Number of mini frames is proportional to the maximum number of nodes in the network. In the present invention, these mini frames are the control slots which are 10% of the total TDMA frame. Every node in the network will have a dedicated slot in the control pool, which is picked by their unique identification number which is assigned based on MAC address of the node. Each node will exchange the management packet in their dedicated control slot for joining the network. Second block is to identify its control slot to exchange the management packet MANET method. Third block is to get authenticated and acknowledged by the other nodes in the network. Fourth block recognizes the new node entry in the topology strategy of the current network and obtain its slots for regular and emergency tactical message transmissions. Finally, fifth block is dynamic slot allocation mechanism for high bandwidth applications and node-role based slot allocation using slot pooling concept.

The Present invention has the following advantages: -
1. Slot sharing in an ad-hoc manner without a need of a coordinator
2. Unique and dynamic TDMA slot reservation based on global network topology, size (x-node network) and QoS needs for data exchange without collision.
3. Matrix index based dynamic slot sharing depending upon active nodes in the network through global knowledge in an ad-hoc manner (master- less/coordinator-less slot allocation)
4. Fuzzy driven optimal neighbour node and relay node selection method for obtaining global topology, with the link metrics that are applicable for ad-hoc networking at sea.
5. Fuzzy driven node-role identification to share slots.
6. Slot pooling concept for providing priority based dynamic bandwidth sharing that improves the throughput and bandwidth utilization.
7. Generic slot sharing usable for any semi-static AdHoc networks.
Preferred embodiments of the invention are described below with reference to the corresponding drawings.
Figure 1-A is an illustration of the time slots division of a TDMA super frame with static and dynamic according to one embodiment of the present invention.
The figure shows the slot structure of a super frame of a Time Division Multiple Access (TDMA) channel. It consists of macro slots as shown in [S2] and mini slots as shown in [S1]. Duration of a mini-slot is half of that of a macro slot. Macro slots are used for data packet exchange. Mini-slots are used for control packet/management packet exchange. Management slots are used for new node joining and reserved for network establishment and management packet exchange. Mini-slots are 10% of the total number of slots of the TDMA frame.
Figure 1-B graphically illustrates the slot pool share of the super frame shown in Figure 1-A into 3 slot pools according to one embodiment of the present invention.
The figure shows the slot categorization of the TDMA frame of FIG. 1-A according to the principles of the present invention of ‘slot pooling’. Slots of the TDMA frame are divided into four pools of slots which are control pool, message pool, relay pool and high bandwidth pool. Among the slots of the TDMA frame, 10% is reserved for control pool as shown in [S3], 45% is reserved for data pool as shown in [S4] and the remaining 45% is equally shared for relay as shown in [S5] and high bandwidth pool, as shown in [S6].

In one embodiment of the present invention relates to a method of dynamically sharing time slots of TDMA channel among nodes of a maritime wireless ad-hoc network, the method comprising: categorizing the time slots of a TDMA channel into a plurality of time slot pools by a slot pooling method, wherein the time slots of the TDMA channel are categorized into static and dynamic slot pools, where the static slot pool is a control pool and the dynamic slot pools are data slot pool, relay pool and high band pool, determining the TDMA slot share of each slot pool based on current active nodes in the network by a ‘x-node configuration’, determining the slot sharing in each slot pool among the nodes of the network by a ‘matrix index method’, selecting a neighbour node among the nodes of the network by an individual node by a ‘fuzzy driven neighbour node selection’ method and selecting a relay neighbour node among the nodes of the network by an individual node by a ‘fuzzy driven relay node selection’ method, where the ‘fuzzy driven relay node selection’ decides relay nodes of the network instantaneously.
The time slots of the TDMA channel for the control pool is reserved for management functions, time slots of the TDMA channel for data pool is reserved for message transmission, voice and emergency transmission, time slots of the TDMA channel for ‘high bandwidth pool’ is reserved and allocated on a priority basis and used for high bandwidth demands and the time slots of the TDMA channel for ‘relay pool’ are shared among the relay nodes. The above said slot pool is common for TDMA frame of any duration which will be repeated continuously for sharing the common channel among multiple MANET nodes.
The slot pooling method equally divides the time slot duration of individual pools of TDMA frame, so that slots of same pool will have same time duration. Slots of different pools need not have same time duration. Slots of each pool are numbered numerically in unique manner so as to distinguish their slots of other pools.
The ‘x-node configuration’ method as described above, wherein the said TDMA slot sharing will have ‘x’ configuration means that the slots of the ‘data pool’ will be shared among ‘x’ nodes of the network that satisfies the equation:
n mod x=0,
where ‘n’ is the total number of slots of the ‘data pool’.
The method ‘x-node configuration’ further comprises of the step to determine the number of relay nodes that share the slots of the ‘relay pool’ by the following equation:

‘m’ is decided by the topology of the current network.
‘x’ is the value decided for the ‘x-node configuration’.

The slots of the ‘high band pool’ are used only for multimedia/video/image transmission among one-hop communication. If ‘x-node’ = 2, the slots of the ‘high band pool’ are equally divided among two nodes. If ‘x-node’ > 2, then slots of ‘high band pool’ is shared among nodes, in such a way that each node will get ‘d’ slots, where ‘d’ is the minimum number of slots required for multimedia communication. Nodes that can utilize the slots of the high band pool will be determined based on user defined priority.
The ‘matrix index method’ as disclosed above comprising the following steps: The slot numbers of each pool are arranged in a matrix format. There will be three types of matrixes called as, data slot map, relay slot map and high band slot map which will be formed with slot numbers of data, relay and high band pool respectively.
The ‘data slot matrix’ will be formed with number of rows equivalent to the value of the ‘x’ in ‘x-node configuration’. Each node in the network will pick one row index out of ‘x’ row indexes of the ‘data slot map matrix’ based on their MAC address. The ‘relay slot matrix’ will have ‘r’ rows and Each node that has been assigned as relay node will pick one index out of ‘r’ row indexes of the relay slot matrix.
A ‘fuzzy driven neighbour node selection’ as disclosed above, where a fuzzy method step is executed in every node to decide their reliable neighbour or one- hop node. As illustrated in FIG. 6, Fuzzy conditions sets are made with link metrics applicable for maritime ad-hoc networking such as bobbling rate, uni- directional link status, link expiration rate and packet error rate. Neighbour node status is decided with the following fuzzy conditions:
checking hello packet recognition time is in same TDMA cycle;
checking uni-directional link status should be zero;
checking link expiration rate should be low;
checking packet error rate should be low; and
checking link duration should be high
A ‘fuzzy driven relay node selection’ as disclosed above, where a fuzzy method step is used to determine ‘relay nodes’ of the network according to the current topology. An individual node can decide its relay status based on its number of nodes, in its neighbour, 2 and 3 hop distance. The fuzzy selection method also includes the parameters as applicable for maritime Ad Hoc networking such as criticality of the nodes position in the network and its reachability to remote nodes of the network. The conditions set of the fuzzy method of relay selection is listed in FIG. 7.
Figure 2 illustrates the TDMA indexing for control slot pool of TDMA super frame according to one embodiment of the present invention.
The figure 2 illustrates the TDMA indexing for control slot pool of TDMA super frame. Every node in the network will get one slot dedicated in the control pool as it enters the network. Every node will be assigned with unique identification number which is defined during the authentication process of tactical/naval communication. This unique identification number is mapped with the MAC address of the radio unit that is participating in the TDMA communication to derive the unique TDMA identity for the radio unit. Hence each radio unit will get a unique number. This identity is referred as TDMA_INDEX as shown in [S7]. Depending upon the total number of nodes, TDMA fame 1-A, will be doubled or tripled.
Figure 3-A is a table showing the descriptions of variables used in one exemplary implementation that describes the dynamic time slot allocation process occurring in each node of the network according to one embodiment of the present invention.
The figure 3-A is a table showing the descriptions of variables used in one exemplary implementation that describes the dynamic time slot allocation process occurring in each node of the network. According to the TDMA_INDEX, the node will transmit its control packet in the mini-slot. Number of active nodes in the network is determined through management packet generated by the MANET method and exchanged through the control slots. Depending upon the number of active nodes in the network, ‘x-node’ configuration of the network is decided that satisfies the equation ‘n mod x=0’, as detailed before ‘x-node’ configuration parameter as noted in [S8] decides the value of the variable ‘TDMA CYCLE COUNT’ of [S9]. If the maximum number of nodes in the network is up to 2, ‘x-node’ configuration is two and ‘TDMA CYCLE COUNT’ will be two. Similarly, for different number of nodes of the network, example values of the ‘x-node’ configuration are as shown in illustration of FIG. 3-A. The ‘data pool’ slots will be equally shared among the number of nodes as per the ‘TDMA CYCLE COUNT’ determined through the table as shown in FIG. 3-A.
‘RELAY COUNT’ is used for determining the slot shares among the nodes that are acting as relay in the current network topology. The value of ‘RELAY COUNT’ is determined by the equation: 'r=([x/2]+m)' as detailed before. The example values of ‘RELAY COUNT’ are as shown in FIG. 3-A [S10]. ‘BUSY COUNT’ is decided based on priority that determines the slot shares among the nodes that request high band width communication. The example values of ‘BUSY COUNT’ are as shown in FIG. 3-A [S11].
Figure 3-B illustrates the data slot matrix for different TDMA configurations of Figure 3-A according to one embodiment of the present invention.
The figure 3-B illustrates the data slot matrix for different TDMA configurations of Figure 3-A. Slots of the ‘data pool’ are grouped in a table called ‘data slot matrix’. For every ‘x- node’ configuration value as shown in FIG. 3-A [S9], different ‘data slot matrix’ is generated. Every ‘data slot matrix’ defines the slots sharing among the number of nodes as per the ‘x-node’ configuration. For example, for the ‘x-node’ configuration of 2, the invention has ‘2 node-data slot matrix’ as shown in FIG. 3-B [S12] where the all slots of ‘data pool’ is shared among 2 nodes and the slot numbers will be listed in a matrix format. Every node will pick one row-index from this matrix. Similarly, the ‘x-node’ configuration of 4, the invention has ‘4 node-data slot matrix’ of FIG. 3-B [S13] and slots of ‘data pool’ will be shared among four nodes. Slot numbers will be listed in a matrix of four rows and each node will pick one row index of the matrix. This matrix of the ‘data slot matrix’ is available with every node, which will be pre-loaded in the data base of the authorized nodes of naval/tactical communication. Basically, ‘data slot matrix’ is a matrix with row indexes equivalent to value of ‘x-node’ configuration and column of this matrix will define the slots numbers of each nodes. As the numbers of active nodes are increasing, the slots shared for each node is gradually decreasing. Slot numbers in each row of the ‘data slot matrix’ are chosen in a way that two consecutive slots of the TDMA frame FIG.1-A are not assigned to the same node. Transmission slots for a node are interleaved to avoid continuous on/off communication.
Slots of a row of the ‘data slot matrix’ will be allocated to one node. Each node in the network can pick one ‘row index’ of the ‘data slot matrix’. The index is decided based on the TDMA_INDEX [S7] of the node. TDMA_INDEX of the other active nodes in the network is known to all active nodes in the network through MANET protocol. Every node will sort the values of the TDMA_INDEX of the active nodes in an ascending order. The method picking the index for each node is what is mentioned as ‘matrix-index’ method according to the present invention. Conditions for slot allocation based on the ‘matrix-index’ method is as follows:
1. The node that has the lowest valued [S7] TDMA_INDEX, will pick the first row of the ‘data slot matrix’
2. The node with next highest value will pick the second row of the ‘data slot matrix’.
3. Step 2 is repeated for all the TDMA_INDEX of the active node.
This procedure is common for any “data slot matrix”. As the total number of active nodes in the network is known, size of the “data slot matrix” is also known to every node. Since the data base of slot sharing of the entire “data slot matrix” is available with every node, the “row index” will be automatically calculated by the node itself based on the TDMA_INDEX of the active nodes of the network.
In ad-hoc networking at sea, challenge will be the instability of the link connectivity among the nodes due to the continuous up and down wave motion of the sea water. Novel fuzzy based neighbour node selection method is introduced for this purpose. Every node will execute the fuzzifier for deciding their one-hop neighbours. Following list of information will be acquired at the fuzzifier to select the neighbour node:
1) Hello packet recognition time
2) Uni-directional link status
3) Link expiration rate
4) Packet error rate
5) Link duration (the length of the time that two nodes stay connected before they move out of transmission range)
For a node to be declared as a neighbour node, following conditions to be satisfied:
1) hello packet recognition time is in same TDMA cycle;
2) uni-directional link status should be zero;
3) link expiration rate should be low;
4) packet error rate should be low; and
5) link duration should be high.
Condition base for the neighbour discovery fuzzifier is tabulated in FIG.6.
Figure 4-A graphically illustrates the division of data/relay slot portion of Figure 1-B according to one embodiment of the present invention.
Figure 4-B is a table that details the sharing of relay slot of Figure 4-A which is available in each node of the network according to one embodiment of the present invention.
Figure 4-C illustrates the relay slot matrix for different TDMA configurations of Figure 3-A according to one embodiment of the present invention.
The figure graphically illustrates the division of data/relay slot portion of Figure 1-B. Slots of 5 ‘relay pool’ with respect to the TDMA frame 1-A, are pre-determined and are as shown in FIG. 4-A. Slots listed in the ‘relay pool’ are as shown in FIG. 4- A [S14]. It will be used by the relay nodes of the network, for relaying the messages of other network. For transmitting its own data packets, the relay nodes will use its own data pool slots assigned through ‘data slot matrix’ as discussed with respect to FIG.3-B. The ‘relay slot matrix’ contains the slots numbers that are shared for different relay nodes in the current network scenario. Similar to ‘data slot matrix’ generation, for every ‘x-node’ configuration, different ‘relay slot matrix’ is generated. For example, for the ‘x-node’ configuration of 4, the present invention has ‘2 node-relay slot matrix’ as shown in FIG. 4-C[S17] and for the ‘x-node’ configuration of 6, the present invention has FIG.4- C/S18 ‘4 node-relay slot matrix’ and so on. The rows of the ‘relay slot matrix’ are equivalent to the values of the ‘RELAY COUNT’ as listed in FIG.4-B [S16]. The value of the ‘RELAY COUNT’ is decided depending upon the active nodes in the network.
The data base of all the different sizes of ‘relay slot matrix’ is available with every node. As the number of active nodes in the network is known to all the nodes in the network, every node will also know that which size of ‘relay slot matrix’ to be chosen. Fuzzy based neighbour discovery method is used to decide the relay status of a node in the current network topology. Each node executes this fuzzy method to get its relay status. The nodes that are identified as ‘relay nodes’ by the fuzzy method will be globally accepted among all nodes and known to all nodes. In a given topology, every node will estimate its relay status based on the conditions tabulated in FIG.7. In a certain topology, there may be many relay nodes. The ‘row index’ will be picked based on the TDMA_INDEX. The conditions for picking the relay slots from the ‘relay slot table’ is as to that of ‘data slot matrix’.
Figure 5-A is a table which describes sharing of high band slot of Figure 4-A according to one embodiment of the present invention.
Figure 5-B shows the high band slot matrix for different TDMA configurations of Figure 3-A according to one embodiment of the present invention.
The figure shows a table which describes sharing of high band slot of Figure 4-A. further, the figure 5-B shows the high band slot matrix for different TDMA configurations of Figure 3-A. Slots of the ‘high band pool’ are assigned for the nodes that require image or multimedia transmission. Only few nodes are permitted to avail multimedia communication. The number of nodes that can participate in the multimedia communication is limited depending upon the number of active nodes in the network. Multimedia communication can be initiated between one hop nodes only. As there are only two nodes the slots of ‘high band pool’ will be equally shared among them S21. If there are more than two nodes in the network, slots of ‘high band pool’ are shared among nodes, in such a way that each node will get ‘d’ slots, where ‘d’ is the minimum number of slots required for multimedia communication. An example slot sharing is shown in FIG. 5, for the use case of 36 slots of ‘high band pool’. Node selection for multimedia communication is decided based on the priority. The number of nodes currently participating in multimedia communication and row index of the ‘high band pool’ which is currently allocated to ‘on-going’ multimedia communication will be updated in the management packet as a part of MANET method. The priority is determined based on the node identification number of the node. The priority can be user-defined for the application purpose. This priority information is pre-loaded in the nodes. Since every node in the network is also aware of the priority index of the other nodes, they themselves will be able to decide their reservation rights for using the ‘high band pool’. If same priority level nodes are contenting for the ‘high band pool’, then the node with lowest TDMA_INDEX will get the priority.
Figure 6 shows a condition/rule base for optimal neighbour node selection fuzzifier according to one embodiment of the present invention.
Figure 7 shows a condition base for optimal relay node selection fuzzifier according to one embodiment of the present invention.
The figure shows a condition base for optimal neighbour node selection fuzzifier and a condition base for optimal relay node selection fuzzifier. In order to introduce a fuzzy system for the inputs of neighbour node selection (FIG.6) and relay node selection (FIG. 7), the triangular based function is used. According to the present invention, every node in the network will get a dedicated slot in the control pool, through which management information will be exchanged among the nodes. Every node will send the following information in the management packet:
Total number of nodes reachable by itself upto four hops
Relay status of self
High band slot occupancy information of self
Unique identification number of self
Nodes in one and two hops
The above parameter is exchanged among all nodes and after the duration every three cycles of TDMA duration, the node connectivity in the entire network will be learnt by each node. This determines multi-hop network forming using the slot sharing method of this invention. If there exists two such networks which use the present invention of slot sharing, then net merger among these networks will happen through the edge node of the network that moves closer to adjacent network. Net merging will happen in a serial way as nodes will be merged one by one to the adjacent network.
Although several embodiments of the present invention have been illustrated in the accompanying drawings and described in the forgoing detailed description, it should be understood that the invention is not limited to the embodiments disclosed, but it is capable of numerous rearrangements, modifications and substitutions without departing from the spirit of the invention as set forth.
Those skilled in this technology can make various alterations and modifications without departing from the scope and spirit of the invention. Therefore, the scope of the invention shall be defined and protected by the following claims and their equivalents.
FIGS. 1-7 are merely representational and are not drawn to scale. Certain portions thereof may be exaggerated, while others may be minimized. FIGS. 1-7 illustrate various embodiments of the invention that can be understood and appropriately carried out by those of ordinary skill in the art.
In the foregoing detailed description of embodiments of the invention, various features are grouped together in a single embodiment for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed embodiments of the invention require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter lies in less than all features of a single disclosed embodiment. Thus, the following claims are hereby incorporated into the detailed description of embodiments of the invention, with each claim standing on its own as a separate embodiment.
It is understood that the above description is intended to be illustrative, and not restrictive. It is intended to cover all alternatives, modifications and equivalents as may be included within the spirit and scope of the invention as defined in the appended claims. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. In the appended claims, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein,” respectively.
,CLAIMS:We Claim:

1. A method of dynamically sharing time slots of TDMA channel among nodes of a maritime wireless ad-hoc network, the method comprising:
categorizing the time slots of a TDMA channel into a plurality of time slot pools by a slot pooling method, wherein the time slots of the TDMA channel are categorized into static and dynamic slot pools, where the static slot pool is a control pool and the dynamic slot pools are data slot pool, relay pool and high band pool;
determining the TDMA slot share of each slot pool based on current active nodes in the network by a ‘x-node configuration’;
determining the slot sharing in each slot pool among the nodes of the network by a ‘matrix index method’;
selecting a neighbour node among the nodes of the network by an individual node by a ‘fuzzy driven neighbour node selection’ method; and
selecting a relay neighbour node among the nodes of the network by an individual node by a ‘fuzzy driven relay node selection’ method, where the ‘fuzzy driven relay node selection’ decides relay nodes of the network instantaneously.
2. The method as claimed in claim 1, wherein the time slots of the TDMA channel for the control pool is reserved for management functions, time slots of the TDMA channel for data pool is reserved for message transmission, voice and emergency transmission, time slots of the TDMA channel for ‘high bandwidth pool’ is reserved and allocated on a priority basis and used for high bandwidth demands and the time slots of the TDMA channel for ‘relay pool’ are shared among the relay nodes.
3. The method as claimed in claim 1, wherein every node which enters in to a network, gets a slot in the control pool, where the control pool sharing is determined based on a MAC identity of the nodes.
4. The method as claimed in claim 1, wherein the slot pooling method equally divides the time slot duration of individual pools of TDMA frame, thus slots of same pool have same time duration, further the slots of each pool are numbered uniquely for distinguishing their slots of other pools.
5. The method as claimed in claim 1, wherein the TDMA time slot sharing has ‘x’ node configuration, where the time slots of the ‘data pool’ is shared among ‘x’ nodes of the network that satisfies the equation:
n mod x=0,
where ‘n’ is the total number of slots of the ‘data pool’.
6. The method as claimed in claim 1, wherein the ‘x-node configuration’ further comprises the step to determine the number of relay nodes that share the slots of the ‘relay pool’ by the following equation:

‘m’ is decided by the topology of the current network.
‘x’ is the value decided as in claim 6 for the ‘x-node configuration’.

7. The method as claimed in claim 1, wherein the time slots of the ‘high band pool’ are used for multimedia/video/image transmission among one-hop communication, where if ‘x-node’ = 2, the slots of the ‘high band pool’ are equally divided among two nodes, if ‘x-node’ > 2, then slots of ‘high band pool’ is shared among nodes, in such a way that each node ‘d’ slots, where ‘d’ is the minimum number of slots required for multimedia communication.

8. The method as claimed in claim 1, wherein the ‘matrix index method’ comprising arranging the slot numbers of each pool in a matrix format.

9. The method as claimed in claim 1, wherein the ‘data slot matrix’ is formed with number of rows equivalent to the value of the ‘x’ in ‘x-node configuration’, where each node in the network picks one row index out of ‘x’ row indexes of the ‘data slot map matrix’ based on their MAC address.

10. The method as claimed in claim 1, wherein the ‘relay slot matrix’ has ‘r’ rows and each node that has been assigned as relay node picks one index out of ‘r’ row indexes of the relay slot matrix.

11. The method as claimed in claim 1, wherein selecting a neighbour node among the nodes of the network by an individual node by a ‘fuzzy driven neighbour node selection’ method has following steps:
checking a hello packet recognition time of other nodes in the network, wherein the hello packet recognition time should be same TDMA cycle as that of the individual node; and
checking a uni-directional link status, a link expiration rate, packet error rate and link duration of other nodes in the network.

12. The method as claimed in claim 1, wherein selecting a relay neighbour node by a node among the nodes of the network by a ‘fuzzy driven relay node selection’ has following steps:


deciding a relay status of individual node based on the number of nodes in the neighbour and hop distance.

Dated this 27th day of March, 2018
FOR BHARAT ELECTRONICS LIMITED
(By their Agent)

(D. Manoj Kumar) IN/PA-2110
KRISHNA & SAURASTRI ASSOCIATES LLP