DESC:FIELD OF INVENTION
[0001] The present disclosure relates generally to a Wireless Sensor Network (WSN) in long coverage and densely deployed scenarios and specifically to clustering of the WSN using Multi-Sequence Synchronous Frequency Hopping (M-SSFH) in a Radio Frequency (RF) network.

BACKGROUND
[0002] A tactical Wireless Sensor Network (WSN) is a modular information sharing network that provides an intelligence-led solution to effective continuous monitoring of wider landscapes. A deployment of the WSN includes a large-scale wireless distributed network of sensor nodes, which are densely deployed over a wide geographical region to monitor and track various aspects of physical targets. Effectively designing and developing such a large-scale network needs a scalable architectural strategy that provides security and mobility. Further, developing protocols for data radio links for such large-scale networks is very challenging and varies largely according to user requirements.
[0003] Conventional techniques of the WSN deployments in hierarchical sensor networks are usable only in short range and smaller landscapes. For instance, U.S. Patent document 7,890,301 B2, titled "Method of Cluster Head Selection in Networks Accessed by Mobile Devices" relates to a method where the probabilistic characteristics of mobile device interaction with nodes of a sensor network are taken into account. This method does not provide any channel access technique for scalability of a network. Therefore, this WSN cannot be scaled.
[0004] U.S. Patent document 2006/0268745 A1, titled "Clustering Method of Wireless Sensor Network for Minimized Energy Consumption" relates to a clustering method to minimize the energy consumption of battery-operated sensor nodes. This technique also does not account for any channel access parameters regarding wireless sensor networks, and hence, limits the scalability and interference resistance of the WSN.
[0005] U.S. Patent 10,524,308 B2 relates to a method for decentralized clustering in wireless sensor networks that is aimed to determine selection of cluster head based on some parametric score.
[0006] US Patent document 2009/0154395 A1 titled “Wireless Sensor Network having Hierarchical Structure and Routing Method Thereof” results in end-to-end delay considering scalability of a mesh network and the routing method.
[0007] All the above-mentioned disclosures relate to selection criteria of cluster heads rather than any method to access the RF channel cooperatively without any interference. Furthermore, these prior arts limit the scalability and density of deployment, and channel utilization efficiency. Grouping of such member nodes into clusters of a sensor network has been widely proposed over the years in order to achieve the network scalability. Every cluster would have a head and/or gateway to collect and convey the information to or from sensor nodes. A cluster head might be pre-assigned or elected dynamically based on the type of sensor networks. Nonetheless, the cluster head must be richer in resources compared to the sensor nodes. Although many clustering methods have been found in the literature, their objective is mainly to establish clusters in order to make energy efficient nodes with node reach-ability. However, most of the conventional methods are limited by certain requirements without any consideration for network coverage and efficient utilization of the RF spectrum among the clusters. Moreover, no conventional technique addresses the concerns of security of data links in terms of the probability of interception.
[0008] Therefore, there is a need for efficient, secure, and scalable technique for clustering WSN in densely deployed geographical areas without interference within the clusters.

SUMMARY
[0009] This summary is provided to introduce concepts related to clustering of Wireless Sensor Networks (WSNs) using Multi-Sequence Synchronous Frequency Hopping (M-SSFH) in a Radio Frequency (RF) network. This summary is neither intended to identify essential features of the present invention nor is it intended for use in determining or limiting the scope of the present invention.
[0010] In an embodiment of the present invention, a system for orthogonal clustering of Wireless Sensor Networks (WSN) using Multi-Sequence Synchronous Frequency Hopping (M-SSFH) in a Radio Frequency (RF) network is disclosed. This system consists of plurality of mobile or static nodes. The plurality of nodes in the said WSN are hierarchically arranged in a plurality of layered clusters, such that each cluster synchronously hops from one orthogonal frequency to another orthogonal frequency with respect to each other at the beginning of every time slot. Each of the plurality of layered clusters includes one designated cluster head cum gateway node (CHCG) node and the plurality of sensor nodes. The WSN is structured as a whole in an orthogonal form of the plurality of layered clusters to provide them with orthogonal access of a permitted RF spectrum such that any two clusters operating on the same RF at any discrete instant of time can be strictly avoided. In addition, a channel sharing strategy of Dynamic Time Division Multiple Access (TDMA) is formulated and designed independently within each cluster. Therefore, the TDMA approach with M-SSFH prevents RF interference even when the multiples of nodes from other clusters are in close proximity and densely deployed. Ultimately, all the said clusters, under a single command post, provide a collaborative combat experience to share information on tactical superiority.
[0011] In another embodiment of the present invention, a method for orthogonal clustering of a Wireless Sensor Network (WSN) using Multi-Sequence Synchronous Frequency Hopping (M-SSFH) in a Radio Frequency (RF) network is disclosed. This method comprises assigning a unique identification number to each cluster from a plurality of layered clusters that consists of a plurality of sensor nodes and a cluster head cum gateway node (CHCG). In addition, each of the clusters must also have a host application server (HAS) connected to a first radio device RLC (Radio of Lower Cluster) and a second radio device RUC (Radio of Upper Cluster), wherein the RUC and the RLC belong to two different clusters. Further, the WSN is structured as a whole in an orthogonal form of the plurality of layered clusters to provide them with orthogonal access of a permitted RF spectrum such that any two clusters operating on the same RF at any discrete instant of time can be strictly avoided. Further, each cluster of the plurality of layered clusters is synchronously hopping from one orthogonal frequency to another orthogonal frequency at the beginning of every time slot. In addition, a channel sharing strategy of Dynamic Time Division Multiple Access (TDMA) is formulated and designed independently within each cluster. Therefore, the TDMA approach with M-SSFH prevents RF interference even when the multiples of nodes from other clusters are in close proximity and densely deployed.
BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS
[0012] The detailed description is described with reference to the accompanying figures.
[0013] FIG. 1 illustrates a schematic architectural diagram of a Wireless Sensor Network (WSN) in accordance with an embodiment of the present invention.
[0014] FIG. 2 illustrates a schematic block diagram of a Cluster Head Cum Gateway (CHCG) in accordance with an embodiment of the present invention.
[0015] FIG. 3 illustrates a schematic diagram of an Internet Protocol (IP) packet in accordance with an embodiment of the present invention.
[0016] FIG. 4 illustrates
[0017] Multi-Sequence Synchronous Frequency Hopping (M-SSFH) for clusters and sensor nodes in a Wireless Sensor Network (WSN) in accordance with an embodiment of the present invention.
[0018] FIGs. 5-6 illustrate flowcharts of a method of clustering a Wireless Sensor Network (WSN) in accordance with an embodiment of the present invention.
[0019] It should be appreciated by those skilled in the art that any block diagrams herein represent conceptual views of illustrative methods embodying the principles of the present invention. Similarly, it will be appreciated that any flow charts, flow diagrams, and the like represent various processes which may be substantially represented in computer readable medium and so executed by a computer or processor, whether or not such computer or processor is explicitly shown.

DETAILED DESCRIPTION
[0020] The various embodiments of the present invention provide a system for clustering of Wireless Sensor Networks (WSNs) using Multi-Sequence Synchronous Frequency Hopping (M-SSFH) in a Radio Frequency (RF) network and a method for clustering of a WSN using M-SSFH in an RF network.
[0021] In the following description, for purpose of explanation, specific details are set forth in order to provide an understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without these details.
[0022] One skilled in the art will recognize that embodiments of the present invention, some of which are described below, may be incorporated into a number of systems.
[0023] However, the systems and methods are not limited to the specific embodiments described herein. Further, structures and devices shown in the figures are illustrative of exemplary embodiments of the present invention and are meant to avoid obscuring of the present invention.
[0024] It should be noted that the description merely illustrates the principles of the present invention. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described herein, embody the principles of the present invention. Furthermore, all examples recited herein are principally intended expressly to be only for explanatory purposes to help the reader in understanding the principles of the invention and the concepts contributed by the inventor to furthering the art and are to be construed as being without limitation to such specifically recited examples and conditions. Moreover, all statements herein reciting principles, aspects, and embodiments of the invention, as well as specific examples thereof, are intended to encompass equivalents thereof.
[0025] Throughout this description, the term “radio device” is includes any apparatus or mechanism adapted to transmit, receive or transmit and receive data through a wireless radio frequency communication network. A radio device is designed to establish communications among the remotely placed Internet Protocol (IP) devices transparently over radio frequency (RF) wireless network. Consequently, the radio device makes a gateway between wireless RF network and Ethernet IP wired network. In the case of wireless communications, the radio device may comprise an RF transmitter, RF receiver, RF transceiver or any combination thereof. Examples of the Wireless communication include, but are not limited to, RF communication, microwave communication, for example long-range line-of-sight communication via antennas. Applications of the said wireless communication networks include, but are not limited to, point-to-point communication, point-to-multipoint communication networks and other such communication networks.
[0026] The present invention provides a system for clustering of Wireless Sensor Networks (WSNs) using Multi-Sequence Synchronous Frequency Hopping (M-SSFH) in a Radio Frequency (RF) network.
[0027] The present invention provides an RF channel sharing technique to establish a collision free, energy efficient, better quality of service (QoS) and secure radio communication and ensure dynamic and efficient utilization of the RF spectrum within a limited frequency band of operation.
[0028] The WSNs can be used to spot target movements and presence of hazardous materials. Moreover, the WSN may also be helpful to monitoring forest fires and detecting floods and earthquakes. The sensor nodes in such an environment have transducers and processors/microcontrollers for data processing and data fusion. These sensor nodes are connected to a central command and control centre using wireless data link radios. A geographical position of such sensor nodes need not be predetermined. Moreover, relative node mobility and density of nodes, scalability and area coverage of the network, volume and type of payload applications, and dynamism of ad-hoc infrastructure, etc. are very critical parameters that decide waveforms and network topology of the WSN. A WSN deployed in inaccessible and hostile terrains must be self-organising, self-healing and multi-functional using appropriate data link network protocols. Further, in case of distributed WSNs, particularly in tactical scenarios, distances between command-post node and terminal sensor nodes may extend up to hundreds of miles. The sensor nodes are usually required to be deployed randomly in an area of interest by forming a radio network in an ad-hoc manner that also needs optimal usage of electrical power in terms of a better energy efficient system.
[0029] Furthermore, since many sensor nodes may observe the same physical phenomenon, a unique speciality of WSNs must be a collaborative effort of sensor nodes to perform detection, measurement and data fusion to produce a common meaningful picture of detected targets instead of pursuing the redundant data flow to the destination node. The sensor nodes must spontaneously cooperate to convey information by detecting, fusing and forwarding packets from source to a destination. Similarly, the nodes should be capable of forwarding a categorical command from source to destination to take an action against the spotted target.
[0030] In such WSNs, voice support in networking mode is also very essential. The networking capabilities must not prevent point-to-point voice communication, whether interoperable with legacy radios or tactical voice for multicasting among the users. Due to the team-oriented nature of the WSNs, communication in groups using multicasting and broadcasting is very important.
[0031] Therefore, the present invention provides a means for a WSN system to establish a collision free, energy efficient, better quality of service (QoS) and secure communication system to ensure dynamic and efficient utilization of the RF spectrum within a limited frequency band of operation. The present invention provides a means for minimizing RF radiated power and propagation time in order to minimize the probability of interception.
[0032] The proposed system and method in the present invention uses Time Division Multiple Access (TDMA) for channel sharing. Consequently, the present invention also deals with the two major and inherent challenges of TDMA in building such WSNs. Firstly, the cooperative phenomenon of sensor nodes mandates the necessity to agree on a common notion of time for scheduling efficient and collision free RF channel access using TDMA across a distributed super network. Second, to cooperatively maximize bandwidth usage within the permitted RF band across the super network while minimizing the interference and probability of jamming and interception.
[0033] In an embodiment of the invention, a system and method for orthogonal clustering of a wider, dense, and scalable tactical WSN is provided. The system provides simultaneous channel access by different clusters of a super network by implementing M-SSFH. The M-SSFH uses multiple orthogonal patterns of frequency hopping having a common set of frequencies makes TDMA by the members within a cluster independently and exclusively with the members of other clusters.
[0034] The WSN is structured in layered clusters with one designated Cluster Head Cum Gateway (CHCG) for each cluster. Having one designated gateway in each cluster also improves the data processing and fusion capability of the network in order to minimize flow of redundant sensor data within the network. The TDMA based on M-SSFH allows a large community of users to share bandwidth efficiently and reliably.
[0035] The subdivision of the WSN into clusters in a layered manner is done in order to cover a larger geographical area with less required radiated power from Power Amplifiers (PA) of the sensor nodes. The small range of required RF communication within a cluster with fast frequency hopping and lesser PA power minimizes the chances of interception and jamming.
[0036] Synchronous frequency hopping is the fundamental need to incorporate a cluster-based approach. The efficient utilization of the entire permitted radio frequency band is also assured by clustering. The clusters are assigned with unique identifiers, such as a unique cluster identifier (Cluster ID), that are useful in opting for one of the predefined frequency hopping sequences to make them mutually orthogonal to each other in terms of channel frequency.
[0037] Synchronous frequency hopping provides dynamic and fast frequency changeover at the same time by all the nodes in the WSN irrespective of the cluster which they belong to. Therefore, as a whole, the network follows M-SSFH that provides multiple orthogonal channels each covering the entire band of permitted RF spectrum. Since the frequency hopping bandwidth itself is much larger than the required signal bandwidth, each channel achieves the exact same RF spectrum spread over the time but in orthogonal sequences of hopping.
[0038] In the present invention, every cluster includes a CHCG. The CHCG is a designated transit gateway for each cluster is required for establishing communication between inter-clusters. The CHCGs are helpful in making upstream and downstream communication between source and destination nodes that are members of different clusters within the WSN. The CHCGs perform data processing and data fusion capability to minimize flow of redundant data within the network. The CHCG monitors activities of the sensor nodes in the cluster for health monitoring. The CHCG may control the radiated RF power of any sensor node to prolong the battery life of the sensor nodes. The CHCG may also switch off any sensor node remotely in case any emergency arises during operations. Each sensor node in the cluster has a priori information of the CHCG of the cluster.
[0039] Furthermore, channel usage by any node within a cluster is non-static such that the channel allocation is done on-demand basis to avoid un-usability of resources. The protocol used in the present invention facilitates data link communication within the sensor nodes of the cluster using Dynamic TDMA (DTDMA). Herein, channel access with respect to members of other clusters can be understood as frequency division channel access (FDMA) at the same time. Using TDMA based on M-SSFH guarantees orthogonally separated radio frequencies in operation among the clusters at any instant of time, which reduces inter-cluster and intra-cluster interferences.
[0040] The channel sharing strategy of TDMA based on M-SSFH prevents interference while the sensor nodes of the other clusters also perform RF transmission at the same time even if the sensor nodes are geographically very close and densely deployed.
[0041] For efficient utilization of the allocated channel to a cluster, the smallest duration of transmission time in TDMA is defined as a time slot. Hence, the time slot is the legitimate and fundamental period of transmission and reception used by the sensor nodes in a cluster. A single time slot can be defined as a period of time allocated to a single node for transmission purposes during which all other nodes within the same cluster will be in receive mode only.
[0042] The present invention provides real time communications with high quality of service (QoS). To accomplish high QoS real time communication, different types of time slots are used in the WSN.
[0043] Dedicated Access Slots (DAS) are slots assigned to the sensor nodes statically depending on the node identification numbers. Each node has one slot in DAS for sharing of network’s topology information.
[0044] Polling Access Slots (PAS) are slots assigned to provide secure digitized voice channels in tactical communications. Control of voice service is provided by the listen and push-to-talk (PTT) protocol.
[0045] Dedicated Reallocation Slots (DRS) are a fixed number randomly indexed slots assigned that every sensor node uses for high priority data. The DRS are assigned to the available sensor nodes only. The sensor nodes use its DRS for very high priority small messages as well as for TDMA management and signalling.
[0046] Dynamic Contention Slots (DCS) are slots that are fully dynamic in nature. Assignment of the DCS depends on the demand and volume of payload needed to be transmitted by the member nodes. The final decision is made by negotiation of consent requests by prioritization or by fair scheduling. The allocation itself is in line with the node's need or demand while ensuring collision free packet transmission.
[0047] For requesting or releasing dynamic allocation of slots within a cluster, TDMA Management Message (TMM) piggybacked with the cluster ID of the cluster is broadcasted by each sensor node periodically that negotiates traffic slots and resolves conflicts within the cluster.
[0048] Moreover, for addressing real time payload information sharing requirements, each sensor node of a cluster gets at least one opportunity to transmit a high priority information payload within a certain period of time referred to as a frame period. Therefore, the frame period is the time duration of an integer multiple of the slot’s duration. There is also a super frame period, a validity time of TMM, which is defined as an integer multiple of the frame period. Therefore, once traffic negotiation is done with common consensus, it remains valid for a period of a super frame only. Consequently, the negotiation of the slot allocation matrix for DCS is done for a frame period, and thereafter, the same matrix is repeated for a super frame period.
[0049] Referring now to the FIG. 1, a schematic architectural diagram of a system (100) for clustering a Wireless Sensor Network (WSN) is shown in accordance with an embodiment of the present invention. The entire WSN is clustered, and each cluster is assigned a unique cluster identifier (Cluster ID). The system (100) includes a plurality of sensor nodes (104, 124, 126, 134, 148, 150, and 152), a plurality of Cluster Head Cum gateway Nodes (CHCG) (also referred to as “transit gateways”)(106, 114, 120, 130, 138, 142, 154, and 156), RF wireless links, and a command-post node (102).
[0050] The sensor nodes (104, 124, 126, 134, 148, 150, and 152) are arranged and numbered according to corresponding clusters. In an example, the sensor nodes (104, 124, 126, 134, 148, 150, and 152) may have to perform similar kinds of responsibilities. The sensor nodes (104, 124, 126, 134, 148, 150, and 152) are grouped in different levels of hierarchy. The sensor nodes (104, 124, 126, 134, 148, 150, and 152) include transducers, i.e., physical sensor devices with a radio device.
[0051] Each CHCG (106, 114, 120, 130, 138, 142, 154, and 156) has one host application server (HAS) and two RF transceivers (also referred to as “radios”). The command-post node (102) has at least one radio and one master HAS. There are wireless radio frequency links (103, 105, 107, 109, 111, 113, 115, and 117) between member nodes. These radio links (103, 105, 107, 109, 111, 113, 115, and 117) are used to communicate with corresponding radios in the same clusters. In the figure, each cluster is assigned with a random but static cluster identifier, i.e., Cluster ID.
[0052] Referring now to the FIG. 2, a schematic block diagram of a CHCG (200) is shown in accordance with an embodiment of the present invention. Each CHCG (200)includes one Host Application Server (HAS) (202), and two radios (210, 212) where the radios (210, 212) are members of two different clusters. The radios (210, 212) are connected to antennae (208, 206) respectively. The Cluster IDs are N1 and N2 that cannot be the same in any case. Furthermore, there is a scope of connecting more user IP applications devices to the CHCGs using L3 switch (204). In an example, for CHCG (106), the radio (110) is the Radio of the Upper Cluster (RUC), and the radio (108) is the Radio of the Lower Cluster (RLC). The RUC and RLC (110, 108) are co-located, and the RUC and RLC(110, 108) communicate with each other through wired Ethernet IP network only through the HAS (202). The sensor nodes (104, 124, 126, 134, 148, 150, and 152) collect information and detect one or more physical quantities/parameters of a target. The sensor nodes (104, 124, 126, 134, 148, 150, and 152) transmit the information to the respective CHCG (106, 114, 120, 130, 138, 142, 154, and 156).
[0053] In an example, the CHCG (200) collects sensor data from multiple sensor nodes that directly have RF data links with the RLC (210). The RLC (210) provides the sensor data to the L3 switch (204) by using the wired Ethernet IP network. The switch (204) conveys the sensor data indicative of the received sensor data to the HAS (202) by way of the wired Ethernet IP network. The HAS (202) processes the sensor data and performs data fusion on the sensor data to remove redundant data from the sensor’s data. The HAS (202) generates a cleaned data having reconstructed packets devoid of any redundant information. The HAS (202) forwards the cleaned data to the switch (204) though the wired Ethernet IP network. The switch (204) forwards the cleaned data including the reconstructed packets to the RUC (212) though the wired Ethernet IP network.
[0054] The HAS (202) performs transit wired networking to virtually connect RUC (210) and RLC (212). The wireless routing of the network is performed by Radio Embedded Routing within the corresponding cluster. Therefore, an external PC is required only for host applications rather than managing the wireless network.
[0055] In an embodiment, an RF channel multiple access technique is provided by the present invention. In the RF channel multiple access technique of the present invention, each member of a cluster shares the RF channel by using TDMA where channel resource allocation is dynamic and is based on the consensus agreed upon by the members of the cluster. The smallest and fundamental measure of transmission time in TDMA is the time slot. During any timeslot, only one node of a cluster transmits RF power and other modes of the cluster are in reception mode only. The RF channel multiple access technique of the present invention provides real time radio data link communication. Additionally, quality of service (QoS) of the communication is maintained by prioritizing the payload and transmitting the prioritized payload accordingly.
[0056] Referring now to FIG. 3 a framework of time slots, frame period and supper frame period is shown in accordance with an embodiment of the present invention. For addressing real time payload information sharing requirements, a frame period (304) is devised to optimize the network data latency in a way that each node gets a chance to transmit at least once in the period of every frame irrespective of the number of requests by the member nodes of the same cluster. There is also a super frame period (302), a validity time of TMM, which is defined as an integer multiple of the frame period. A tentative format of a packet (308) can be used for transmission during any allotted time slot (306).
[0057] Referring now to FIG. 4, a high-level concept of M-SSFH is shown in accordance with an embodiment of the present invention. The block level illustration in FIG. 4 shows orthogonal RF channel access by different clusters. The entire permitted frequency band is distributed two-dimensionally. The frequency distribution on time axis (404) is defined for a frequency hopping pattern within a channel assigned to a cluster. Therefore, RF channel spreading is done as much as possible to cover the entire permitted band by using frequency hopping used by TDMA (406) within the cluster. On the other side, the same listed frequencies are also distributed on frequency axis (408) but in different orders depending on sequence number (410). Therefore, the distribution of frequency patterns is classified in each row in the figure showing a RF channel. As shown in FIG. 4, each row of the two-dimensional distribution covers the exact same frequency spreading like others. To make an orthogonal assignment of frequencies during a given time slot, all the frequencies in that column must be different and isolated by a step size equal to at least the occupied bandwidth of the transmitted RF signal. As a whole, to provide channel access to N clusters, at least N number of frequencies is required to be filled in a global table. Preferably, the decision of frequencies is done in such a fashion so that listed frequencies spread uniformly throughout the permitted RF spectrum. Now the same global table is assigned to rows as well as to columns but in different orders defined by sequence numbers.
[0058] The WSN as a whole is structured in orthogonal layered clusters (c1-cn) to provide them orthogonal access of the permitted RF spectrum such as to strictly avoid operating of any two clusters at same radio frequency at any discrete instant of time. The RF channel multiple access technique strategy of M-SSFH prevents interference while the sensor nodes (104, 124, 126, 134, 148, 150, 152) of the different layered clusters (c1-cn) are in close proximity in a dense deployment scenario. The M-SSFH assures maximum and exact similar RF spectrum spreading over the time but in orthogonal sequences of hopping by each cluster. The M-SSFH provides guaranteed orthogonal separation of radio frequencies in operation among the layered clusters (c1-cn) always at any instant of time.
[0059] Therefore, operating frequencies of every cluster at any point of time remains orthogonal with respect to other clusters operating with their own Dynamic TDMA (DTDMA) allocations. The TDMA access by any sensor nodes (104, 124, 126, 134, 148, 150, or 152) of the concern cluster on on-demand basis makes the TDMA dynamic in nature and avoids un-usability of channel resources, thereby facilitating DTDMA. In addition, the inclusion of the DTDMA provides assurance of QoS of priority application payloads in terms of guaranteed and priority-based delivery of packets of the priority application.
[0060] For the time synchronization between the layered clusters (c1-cn),a common notion of time for network time referencing is decided by the command-post node (102) either by using universal time reference provided by Global Positioning System (GPS) or another source of stable clock. The M-SSFH improves the scope of network scalability as a whole either by adding more number of the sensor nodes (104, 124, 126, 134, 148, 150, 152) in existing layered clusters (c1-cn) or by adding more number of layered clusters (c1-cn) in the WSN depending on the number of frequencies being used in M-SSFH.
[0061] The system (100) covers a large number of the sensor nodes (104, 124, 126, 134, 148, 150, 152) densely deployed in a larger geographical area to share a permitted RF spectrum very efficiently with lesser required radiated RF power from Power Amplifiers (PA).Moreover, the combination of M-SSFH and the low PA power requirement to transmit effectively combats the potential for interception, spot jamming, and mutual interference.
[0062] Referring now to FIGs. 5-6, flowcharts of a method of clustering the WSN are shown in accordance with an embodiment of the present invention.
[0063] At Step 502, layered clusters (c1-cn) are formed with a designated cluster head (CHCG) in each cluster. Accordingly, the sensor nodes (104, 124, 126, 134, 148, 150, 152) are assigned in those clusters (c1-cn).
[0064] At Step 504, at the beginning of every time slot (306), each cluster of the layered clusters (c1-cn) synchronously hops from one orthogonal frequency to another orthogonal frequency with respect to other clusters in the network.
[0065] At Step 506, the RF transceiver of RLC (210) of the CHCG (200) placed in a cluster receives the sensor data from the sensor nodes which are the member of this cluster through RF data link.
[0066] At Step 508, the L3 Ethernet switch (204) receives the sensor data from the RLC (210) over the wired local Ethernet IP network.
[0067] At Step 510, the switch (204) forwards the sensor data to the HAS (202) over the local Ethernet IP network.
[0068] At Step 602, the HAS (202) removes redundant data followed by processing and conditioning of data, referred as data fusion, received from the multiple sensors which may be located very closely, and which detect and report data of the same target.
[0069] At Step 604, the HAS (202) generates the cleaned information reported by all the member nodes of the cluster in the previous or current frame cycle.
[0070] At Step 606, the HAS (202) forwards the said information to the switch (204) over the Ethernet IP network.
[0071] At Step 608, the switch (204) forwards the said information to another RF transceiver (212), referred as RUC which is the member of another cluster (through RF data link),over the Ethernet IP network.
[0072] In operation, the present invention provides subdividing the WSN into clusters in the layered manner to cover a larger geographical area with lesser required radiated RF power. The WSN includes a large-scale wireless distributed network of a plurality of sensor nodes, which are densely deployed over a wide geographical region to monitor and track various aspects of the physical targets. The sensor nodes have sensing devices and processors or microcontrollers for data processing and data fusion. The sensor nodes are connected to a central command and control centre using wireless data link radios.
[0073] In operation, the present invention provides the RF channel multiple access technique using the DTDMA based on the M-SSFH in such clusters that facilitate data link communication within each cluster using DTDMA whereas operating frequencies of every cluster at any point of time remains orthogonal with respect to other clusters operating with their own DTDMA allocations. As a whole, the system follows M-SSFH that provides multiple orthogonal channels each covering the exact same band spreads of the permitted RF spectrum. The clustering approach of the present invention provides a means for minimizing Power Amplifier (PA) radiated power and RF propagation time that minimizes the probability of interception. In view of the fact that a transit gateway (CHCG) is designated in each cluster that establishes a wired communication over IP between inter-clusters. The CHCGs are also used for improving the data processing and data fusion capability of the system for minimizing flow of redundant data within the network.
[0074] Advantageously, the present invention provides a means for the WSN system to establish a collision free, better QoS, and secure communication to ensure dynamic and efficient utilization of spectrum within a permitted RF spectrum.
[0075] The foregoing description of the invention has been set merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to a person skilled in the art, the invention should be construed to include everything within the scope of the invention.
,CLAIMS:
1. A system (100) for orthogonal clustering of Wireless Sensor Networks (WSN) using Multi-Sequence Synchronous Frequency Hopping (M-SSFH) in a Radio Frequency (RF) network, said system (100) comprising:
a plurality of nodes including mobile nodes or static nodes, wherein the nodes are categorized as a plurality of sensor nodes (104, 124, 126, 134, 148, 150, 152), a plurality of cluster head cum gateway nodes (CHCG) (200), and a command-post node (102);
wherein the plurality of nodes in the said WSN are hierarchically arranged in a plurality of layered clusters (c1-cn) such that each cluster synchronously hops from one orthogonal frequency to another orthogonal frequency with respect to each other at the beginning of every time slot (306);
each of the plurality of layered clusters (c1-cn) includes one designated CHCG node, and the plurality of sensor nodes;
structuring the WSN as a whole in an orthogonal form of the plurality of layered clusters (c1-cn) to provide them orthogonal access of a permitted RF spectrum;
formulating and designing a channel sharing strategy of Time Division Multiple Access (TDMA) independently within each cluster;
preventing RF interference even when the plurality of sensor nodes (104, 124, 126, 134, 148, 150, 152) of other clusters are in close proximity and densely deployed by using TDMA strategy with M-SSFH.

2. The system (100) as claimed in claim 1, wherein a node comprises an onboard radio device which consists of at least one controller, one FPGA, RF transceiver, and Ethernet IP interface module, to transmit/receive the data wirelessly over RF link.

3. The system (100) as claimed in claim 1, wherein the cluster head cum gateway node (CHCG) (200) comprises:
one host application server (HAS) (202) along with two radio devices which includes a first radio device (RLC) (210) and a second radio device (RUC) (212);
a switch (204) in wired communication with the first and second radio devices (210, 212), said switch (204) configured to communicate over local Ethernet IP network, wherein the first and second radio devices (210, 212) are connected to a local HAS over the switch (204);
the first radio device (RLC) (210) placed in RF data link in a first cluster to communicate with one or more sensor nodes in the first cluster;
the second radio device (RUC) (210) placed in RF data link in a second cluster to communicate with a cluster head of the second cluster;

4. The system (100) and method as claimed in claim 1, wherein each sensor node (104, 124, 126, 134, 148, 150, 152) comprises:
a transducer to detect one or more physical quantities that include a target, an object, a phenomenon;
a controller configured to generate the sensor data indicative of the detected physical quantities; and
a radio device to transmit/receive the sensor data wirelessly over an RF link.

5. The system (100) as claimed in claim 1, wherein the command-post node (102) comprising a HAS (202) includes a wired IP connection with the onboard radio devices.

6. The system (100) as claimed in claim 1, wherein each HAS (202) is configured to:
reduce the flow of redundant and correlated data received from the plurality of sensor nodes using data processing and fusion;
generate cleaned data; and
forward the cleaned data to the RUC (210) via the switch (204) over the local Ethernet IP network.

7. The system (100) as claimed in claim 1, wherein the radio frequencies are a part of a plurality of orthogonal frequencies (f1-fN) within a predetermined RF spectrum such that every cluster of the plurality of layered clusters (c1-cn) operates on a unique orthogonal frequency.

8. The system (100) as claimed in claim 1, wherein channel access by any node of layered cluster (c1-cn) is on demand basis only in order to make dynamic slot assignment to avoid un-usability of channel resources within said cluster in a way of Dynamic Time Division Multiple Access (DTDMA). Furthermore, the DTDMA strategy also signifies the quality of service assurance in terms of guaranteed and priority based delivery of packets.

9. The system (100) as claimed in claim 1, wherein no two clusters operate at same frequencies in same time slot, and wherein no two nodes within a cluster transmit in same time slot, thereby providing each cluster of the plurality of layered clusters (c1-cn) with an orthogonal access to full spread of the RF spectrum without interference from a proximate cluster in a dense geographical deployment.

10. A method for orthogonal clustering of a Wireless Sensor Network (WSN) using Multi-Sequence Synchronous Frequency Hopping (M-SSFH) in a Radio Frequency (RF) network, said method comprises:
assigning a unique identification number to each cluster from a plurality of layered clusters (c1-cn) that consists of a plurality of sensor nodes (104, 124, 126, 134, 148, 150, 152) and a cluster head cum gateway node (CHCG) (200) having a HAS (202) connected to a first radio device (RLC) (210) and a second radio device (RUC) (212), wherein the RUC and the RLC belong to two different clusters;
structuring the WSN as a whole in an orthogonal form of the plurality of layered clusters (c1-cn) to provide them orthogonal access of a permitted RF spectrum;
synchronously hopping, by each cluster of the plurality of layered clusters (c1-cn), from one orthogonal frequency to another orthogonal frequency at the beginning of every time slot (306);

11. The method as claimed in claim 10, comprising scaling by adding more number of sensor nodes to one or more clusters of the plurality of layered clusters (c1-cn) and/or by adding more number of clusters in the WSN depending on the number of orthogonal frequencies being used in the M-SSFH.

12. The method as claimed in claim 10, wherein the radio frequencies are a part of a plurality of orthogonal frequencies (f1-fN) within a predetermined RF spectrum such that every cluster of the plurality of layered clusters (c1-cn) operates on a unique orthogonal frequency.

13. The method as claimed in claim 10, comprising:
persuading orthogonality in frequencies by maintaining minimum separation of the radio frequencies in operation among the plurality of layered clusters(c1-cn) at any instant of time;
operating Time Division Multiple Access (TDMA) by each of the plurality of sensor nodes within each cluster of the plurality of layered clusters (c1-cn), wherein the operating frequencies of each cluster at any point of time remains orthogonal with respect to other clusters of the plurality of layered clusters (c1-cn) operating with their own dynamic TDMA allocations.

14. The method as claimed in claim 10, wherein a common notion of time for network time referencing is determined by the command-post node (102) by using universal time reference provided by global positioning system (GPS) or by using any co-operative time synchronization protocol for such a clustered network.

15. The method as claimed in claim 10, wherein one or more time slots is dynamically assigned to each sensor node in each cluster of the plurality of layered clusters (c1-cn) for transmitting data on radio frequencies of given set of orthogonal frequencies using Dynamic Time Division Multiple Access (DTDMA) within said cluster.

16. The method as claimed in claim 10, wherein no two clusters operate at same frequencies in same time slot, and wherein no two sensor nodes within a cluster transmit in same time slot, thereby providing each cluster of the plurality of layered clusters (c1-cn) with an orthogonal access to full spread of the RF spectrum without interference from a proximate cluster in a dense geographical deployment.