AU2021200324A1 - Underwater self-organizing network layered cooperative routing method and a system achieving the same - Google Patents

Underwater self-organizing network layered cooperative routing method and a system achieving the same Download PDF

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AU2021200324A1
AU2021200324A1 AU2021200324A AU2021200324A AU2021200324A1 AU 2021200324 A1 AU2021200324 A1 AU 2021200324A1 AU 2021200324 A AU2021200324 A AU 2021200324A AU 2021200324 A AU2021200324 A AU 2021200324A AU 2021200324 A1 AU2021200324 A1 AU 2021200324A1
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Jie Chen
Lu Chen
Yifan Hu
Hailin LIU
Bin LV
Yujiao SUN
Junhe Wan
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Institute of Oceanographic Instrumentation Shandong Academy of Sciences
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    • H—ELECTRICITY
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    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W40/00—Communication routing or communication path finding
    • H04W40/02—Communication route or path selection, e.g. power-based or shortest path routing
    • H04W40/12—Communication route or path selection, e.g. power-based or shortest path routing based on transmission quality or channel quality
    • H04W40/16—Communication route or path selection, e.g. power-based or shortest path routing based on transmission quality or channel quality based on interference
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    • G06F18/2321—Non-hierarchical techniques using statistics or function optimisation, e.g. modelling of probability density functions
    • G06F18/23213—Non-hierarchical techniques using statistics or function optimisation, e.g. modelling of probability density functions with fixed number of clusters, e.g. K-means clustering
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W40/00—Communication routing or communication path finding
    • H04W40/02—Communication route or path selection, e.g. power-based or shortest path routing
    • H04W40/22—Communication route or path selection, e.g. power-based or shortest path routing using selective relaying for reaching a BTS [Base Transceiver Station] or an access point
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W40/00—Communication routing or communication path finding
    • H04W40/24—Connectivity information management, e.g. connectivity discovery or connectivity update
    • H04W40/32—Connectivity information management, e.g. connectivity discovery or connectivity update for defining a routing cluster membership
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
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    • Y02D—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
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    • Y02D30/70—Reducing energy consumption in communication networks in wireless communication networks

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Abstract

The present invention provides an underwater self-organizing network layered cooperative routing method and a system, wherein intra-cluster nodes transmit collected data to a corresponding cluster-head node, the cluster-head node transmits the integrated data to another cluster-head node in an upper layer, data is transmitted through cluster-head nodes layer by layer and eventually channeled to a node on a water surface layer by a last cluster-head node; and the node on the surface layer forwards data to a nearest sink node on the water surface; the intra-cluster nodes includes: source node, relay node and destination node; the source node broadcasts to the relay nodes and the destination node in the meanwhile, and a noise threshold is used to determine the quality of transmission signal at the destination node; if the quality of the transmission signal received at the destination node is lower than the noise threshold, the relay nodes are activated for cooperative data transmission. The method could improve the data transmission rate and survivability of the underwater self-organizing sensor network; and therefore a solid foundation is being established for the application of underwater self-organizing sensor network to practical seabed observation network. Drawings: 0------ ----- - . -- - - -- - - - -- - - - -- - - (M ikNoeSno Nod Suc e t natin-edNd Nod Clse Direct), Rea Ae wt S D I ne rt 1~*'~ , 1 0 i" I ~ aR2 El Sorc Node Ray Nod MD DetntinNd C W .

Description

Drawings:
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Underwater Self-Organizing Network Layered Cooperative Routing Method and a System Achieving the Same
Technical Field
The present invention relates to the technical field of underwater self-organizing network, and in particular to an underwater self-organizing network layered cooperative routing method and a system achieving the same.
Background
Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of common general knowledge in the field.
The ocean is vast, which provides abundant resources; today ocean exploration has become a vibrant domain of research. In accordance with one aspect, with the development of technology, self-organizing sensor networks have adapted to underwater environment and formed underwater wireless sensor networks which are typically used in underwater observation, and mainly in deep sea environment. Due to the fact that the absorption of radio waves in water causes that the signal strength is rapidly attenuated, underwater acoustic communication is preferably employed in such self-organizing sensor networks. But beneath the water acoustic signals have a longer end-to-end delay and bandwidth is limited due to attenuation. Therefore how to develop a high-quality underwater routing mechanism is an important issue in the area of research. Especially, in the course of underwater data transmission, data signals probably suffer fading and path loss which further results in failing to reach destination and a high bit error rate.
In the process of implementing the present invention, the inventor found the following technical problems in the prior art:
Underwater routing protocols could be divided into a plurality of types, such as sorted according to a cooperative routing protocol and a universal routing protocol based on whether or not a cooperation mechanism is being incorporated into. With regard to the universal routing protocol, a depth-based DBR (Depth Based Routing) is one of the classic algorithms in which percept node depths are considered as a forwarding basis, which is simple, easy to understand but consumes a lot of energy. On the basis of DBR, S.Gul et al. develops a lightweight depth-based Routing protocol (LDBR) capable of minimizing energy consumption, but neither routing fault tolerance nor recovery algorithm is incorporated into. Taking cross-layer transmission into consideration, J. Liu et al. proposes an energy-saving cross-layer routing protocol (RECRP) in which it is unnecessary to examine node location, this algorithm could save energy but the link transmission quality is ignored. S. H. Ahmed provides an intelligent protocol for directional flooding, which includes angle and threshold adaption to dynamically reflect QoS requirements but increases communication cost. Z.Jianan et al. discloses a routing protocol based on vector and energy, in which priorities are determined in the first according to vector distances and then transmission is performed combining the factor of energy, but this algorithm fails to consider the number of survived nodes and death nodes. With regard to the cooperative routing protocol, relay nodes and master nodes are established to realize data transmission from source to sink. The cooperative routing protocol improves transmission reliability and data integrity but increases network energy consumption. For example, S.Ahmed et al. proposes an adaptive cooperation protocol in which a coordinate transmission is performed by the match of nodes with a unidirectional antenna to reduce network overhead, but end-to-end delay is increased. T.Tayyaba et al. aims at reducing energy consumption of cooperative communication by introducing mobile sink nodes. Since relay selection seriously affects network performance, this algorithm requires to be further improved to overcome its limitation. A. Ahmad et al. provides a collaborative energy-saving routing protocol (Co-EEUWSN), which jointly optimizes the transmission power of the physical layer and the network layer, thereby improving a data arrival rate but introducing noise problems. In summary, in underwater observation networks, there is an urgent need for a more appropriate underwater self-organizing network routing method which could comprehensively consider factors as energy consumption, signal-to-noise ratio transmission rate and the like.
Brief Summary
In order to solve the deficiencies of the prior art, the present invention provides an underwater self-organizing network layered cooperative routing method and an underwater self-organizing network layered cooperative routing system.
In one aspect, the present invention provides an underwater self-organizing network layered cooperative routing method.
The underwater self-organizing network layered cooperative routing method includes:
part of nodes of an underwater self-organizing sensor network are divided into cluster-head nodes and intra-cluster nodes; wherein in one cluster, the intra-cluster nodes communicate with each other in a cooperative manner and transmit collected data to a corresponding cluster-head node; each cluster-head node integrates data and transmits the integrated data to another cluster-head node in an upper layer; data is transmitted through cluster-head nodes layer by layer and eventually channeled to a node on a water surface layer by a last cluster-head node; and the node on the surface layer forwards data to a nearest sink node on the water surface;
wherein the intra-cluster nodes communicate with each other in a cooperative manner and transmit collected data to the corresponding cluster-head node includes: setting the intra-cluster nodes participating in communication respectively as source node, relay node and destination node; each source node broadcasts to the relay nodes and the destination node in the meanwhile, and a noise threshold is used to determine the quality of transmission signal at the destination node; if the quality of the transmission signal received at the destination node is lower than the noise threshold, the relay nodes are activated for cooperative data transmission.
In another aspect, the present invention also provides an underwater self-organizing network layered cooperative routing system.
The underwater self-organizing network layered cooperative routing system includes: cluster-head nodes and intra-cluster nodes; the cluster-head nodes and the intra-cluster nodes are deployed in an underwater self-organizing sensor network; in which a cluster area is selected in each layer and each cluster area contains one cluster-head node and a plurality of intra-cluster nodes; the intra-cluster nodes communicate with each other in cooperation and transmit collected data to the corresponding cluster-head node; the cluster-head node integrates data and transmits the integrated data to a cluster-head node in an upper layer, the integrated data is transmitted through cluster-head nodes layer by layer and eventually channel to a node on a water surface layer by a last cluster-head node, and the node on the surface layer forwards data to a nearest sink node on the water surface.
The intra-cluster nodes communicate with each other in cooperation and transmit the collected data to the corresponding cluster-head node; the intra-cluster nodes comprise a source node, relay nodes and a destination node.
The source node broadcasts to the relay nodes and the destination node in the meanwhile and a predetermination is performed at the destination node to evaluate the transmission signal quality by comparing it with a noise threshold.
If the quality of the signal received at the destination node is lower than the noise threshold, the relay nodes are activated for cooperative data transmission that is for backup and retransmission of data packets.
Compared with the prior art, the beneficial effects of the present invention are:
1. Aiming at improving the stability and reducing energy consumption of the underwater self-organizing sensor network, the present invention proposes a layered cooperative routing method. Cooperative routing is incorporated into to improve the accuracy of data packets received, and the hierarchical routing further could balance energy consumption. 2. The relay cooperation based on cooperative routing is added to the data transmission phase, so that the source node can send the same data through multiple paths, and accordingly the destination node could receive rate data packets with low bit error. Compared with traditional layered protocols, cooperative routing can replace ordinary multi-hop transmission and guarantee the link quality of underwater channels. 3. The average clustering algorithm is used for clustering nodes, and the conditional probability can be referred to as selecting the cluster-head node. In the process of data transmission, the signal is being amplified and backed up in a data packet by the relay nodes so the loss of packet could be avoided, thereby improving the data transmission rate and survivability of the underwater self-organizing sensor network; and a solid foundation is being established for the application of underwater self-organizing sensor network to practical seabed observation network.
Brief Description of the Drawings
The drawings, which are a part of the application, are used to provide a further disclosure of the application. The exemplary embodiments and description of the application are used for further explanation but do not constitute an improper limitation of the application.
Fig. 1 shows an underwater self-organizing network model according to one aspect of the present invention;
Fig. 2 shows an underwater cooperative routing model according to one aspect of the present invention;
Fig. 3 shows an example of intra-cluster cooperation;
Fig.4 shows the selection of relay nodes and the destination node;
Fig. 5 is a flowchart of an underwater self-organizing network layered cooperative routing method according to one aspect of the invention.
Detailed description
It should be pointed out that the following detailed descriptions are all exemplary and are intended to provide further descriptions of this application. Unless otherwise indicated, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present application belongs.
It should be noted that the terms used here are only for describing specific implementations, and are not intended to limit the exemplary implementations according to the present application. In addition, it should also be understood that when the terms "comprising" and/or "including" are used in this specification indicate features, steps, operations, devices, components, and/or combinations thereof.
Embodiment 1: the present embodiment provides an underwater self-organizing sensor network layered cooperative routing method.
The underwater self-organizing sensor network layered cooperative routing method includes following steps: part of nodes of an underwater self-organizing sensor network are divided into cluster-head nodes and intra-cluster nodes, wherein the intra-cluster nodes communicate with each other in a cooperative manner and transmit collected data to a corresponding cluster-head node; each cluster-head node integrates data and transmits the integrated data to another cluster-head node in an upper layer; data is transmitted through cluster-head nodes layer by layer and eventually channeled to a node on a water surface layer by a last cluster-head node; and the node on the surface layer forwards data to a nearest sink node on the water surface.
In the method, the intra-cluster nodes communicate with each other in a cooperative manner and transmit collected data to the corresponding cluster-head node includes: setting the intra-cluster nodes participating in communication respectively as source node, relay node and destination node, wherein each source node broadcasts to relay nodes and a destination node in the meanwhile, and a noise threshold is used to determine the quality of transmission signal at the destination node.
If the quality of the transmission signal received at the destination node is lower than the noise threshold, the relay nodes are activated for cooperative data transmission.
Further, the step that dividing part of nodes of an underwater self-organizing sensor network into cluster-head nodes and intra-cluster nodes comprises:
SI: Deploying sensor nodes underwater to form an underwater self-organizing sensor network;
S2: Dividing the underwater self-organizing sensor network into several layers; wherein a layer closest to the water surface is defined as a water surface layer; nodes in the water surface layer are not clustered; and a cluster area is selected in each non-surface layer; a cluster-head node is elected in each cluster area; each cluster area contains one cluster-head node and a plurality of intra-cluster nodes.
Further, the method further includes: after completing a round of data transmission, each cluster-head node CH determines an average cluster energy according to remaining energy of cluster members; if the average cluster energy determined by one of the cluster-head nodes is less than a network energy threshold, the cluster area of the layer where the cluster-head node in is reconstructed and a new cluster-head node is elected and a routing information is updated.
Further, the Step S1 that deploying sensor nodes underwater to form an underwater self-organizing sensor network comprises sensor nodes are randomly anchored underwater to form a self-organizing sensor network.
Further, each sensor node is provided with a depth sensor configured to detect a depth of the sensor node.
Further, in the Step S2 that the underwater self-organizing sensor network is divided into several layers includes: the underwater self-organizing sensor network is divided into several layers according to a set transmission radius.
Further, in the Step S2 that dividing the underwater self-organizing sensor network into several layers includes:
LN = Darea
wherein LN representing the number of layers, Darea representing a depth range of an area to be monitored and W representing a transmission diameter of a sensor node;
Nnum = mod(LN) (2)
wherein Nnum representing a serial number of the layer where a sensor node in and Ndpt representing the depth of the sensor node.
Further, in the Step S2 that selecting a cluster area in each non-surface layer includes: selecting a cluster area in each non-surface layer by a clustering algorithm.
Further the selection of a cluster area in each non-surface layer by a clustering algorithm comprising:
S201: Selecting a node as an initial cluster center K1 and a node as farther as possible from K1 as a second cluster center K2;
S202: Selecting a node as farther as possible from the initial cluster center K1 and the second cluster center K2 as a third cluster center K3, wherein K3 is a maximum value among min(d(K3, K1), d(K3, K2));
Selecting a node as farther as possible from K1, K2, and K3 as a fourth cluster center K4, wherein K4 is a maximum value among min(d(K4,K1),d(K4,K2),d(K4,K3)); and selecting K cluster centers in a similar fashion.
S203: after obtaining the K clustering centers, sensor nodes in each non-surface layer are clustered by an average clustering algorithm to obtain the cluster area.
Further in the Step S2 that the election of a cluster-head node in each cluster area specifically includes: electing a cluster-head node by using a Bayesian formula.
Further the election of a cluster-head node by using a Bayesian formula includes:
S211: Calculating a Bayesian probability according to remaining energy, energy consumption rate and link quality of every sensor node within the cluster area.
S212: a node greater than or equal to the Bayesian probability is regarded as the cluster-head node.
S213: nodes less than the Bayesian probability are regarded as intra-cluster nodes.
It should be understood that the Bayesian probability is calculated based on a plurality of attribute values including the remaining energy, energy consumption rate and link quality of every sensor nodes in the cluster area, and the Bayesian probability is expressed:
SI(3)
ej= "# +1 Wherein Pi is a posterior probability when the ith node being elected as the cluster-head node, Pi; is a probability of the jth attribute value of the ith node and a represents the number of node attribute values.
Further, the method includes: if the quality of the transmission signal received at the destination node is higher than the noise threshold, a direct transmission is performed.
Further, the quality of the transmission signal received at the destination node is expressed as a ratio of a power of the transmission signal received at the destination node to a noise power.
Further, if the quality of the transmission signal received at the destination node is lower than the noise threshold, the relay nodes are activated for a cooperative data transmission, which is expressed by formulas:
YRD (f)= aYSR (f)RD nRD(f) (4)
YD YSD Wf+YRD(f (5)
wherein a is an amplification factor, a= Eb represents an energy of signal
transmitted; No is the power spectral density of the noise.
Further, the selection criteria of the relay nodes and the destination node are: in the process of data transmission, each node obtains its own depth information and depth information of other nodes and stores a nearest node to a neighbor node set of its own.
The relay nodes and the destination node are selected based on a Signal-Noise-Ratio (SNR) standard.
Further, the selection of the relay nodes and the destination node based on the SNR standard specifically includes:
Presetting a depth reference dth; selecting m sensor nodes with highest remaining energy which are within the boundary specified by the depth reference dth as candidate relay nodes;
Selecting n sensor nodes with the highest remaining energy which are out of the boundary specified by the depth reference dth as candidate destination nodes;
Selecting the destination node from the candidate destination nodes;
After the selection of the destination node, combining a depth difference between the source node and the destination node, the relay nodes are selected from the candidate relay nodes.
In the selection of the destination node from the candidate destination nodes, a selection formula used is:
f(VD) = PD x Er/Di (6)
, in which a VD corresponding to a maximum value of f(vD) is the optimal destination node.
In the process of selecting the relay nodes from the candidate relay nodes by combining the depth difference between the source node and the destination node after the selection of the destination node, a selection formula used is:
f(VR) =PRxEri X YSRi/DSD (7)
, wherein f(vD) is a formula for selecting the destination node,f(vR) is a formula for selecting the relay nodes, PD is a destination node density, namely a ratio of the number of nodes covered by a circular area with the transmission radius r to the number of nodes in the layer, expressing as PD = Nr/Ni; PR is a relay node density, namely a ratio of the
number of nodes covered by a set depth value dth , preferably dth = 4 r , to the number
of nodes within the circular area with the transmission radius r, expressing as PR= Ndth/Nr,wherein a VR corresponding to a maximum value of f(vR) is the optimal relay node.
An underwater network model of the present invention is described as follows.
For an underwater self-organizing sensor network, a main goal of routing protocol design is to reduce network energy consumption and increase throughput. The energy of sensor nodes deployed underwater is constrained because the batteries barely could be replaced. In terms of energy conservation, the feasibility of cluster-based methods has been proven. The present invention firstly establishes an underwater network model in which a hierarchical manner is being adopted to divide the network into layers, shown in Fig. 1. Sensor nodes are randomly anchored in a self-organizing sensor network and the depth information of each node is known, which is collected by depth sensors provided on the sensor nodes. Taking energy balance into consideration, nodes close to the water surface are not clustered which are defined as the water surface layer. The water surface layer is configured to forward data packets received from underwater cluster-head nodes to sink nodes. Other nodes are disposed in the network hierarchically according to a given transmission radium and each cluster area includes a cluster-head node (CH) and a plurality of intra-cluster nodes. Intra-cluster nodes communicate with each other in cooperation and transmit collected data to the corresponding cluster-head node; the cluster-head node integrates data and sends the integrated data out; the integrated data is transmitted through cluster-head nodes layer by layer and eventually channeled to the nearest sink node. For those sink node on the water, acoustic communication could be used as an underwater communication manner and radio communication could be used as a communication manner on or above the water surface. When all of nodes have completed data transmission to the sink node, one cycle ends which is also defined as a round.
An underwater cooperative routing model of the present invention is described in detail as follows:
The working environment for an underwater self-organized network is complicated; typically a direct communication between two nodes is prone to be affected by seawater flow leading in loss of data, or be hindered by plankton. Collaboration is an effective way to solve such problems. Fig. 2 shows an underwater cooperative routing model including a source node, a destination node and relay nodes, wherein the source node broadcasts to the relay nodes and the destination node in the meanwhile and a noise threshold is used to determine the quality of transmission signal at the destination node, to be specific the quality of transmission signal is determined by a SNR noise threshold yo. If the quality of transmission signal received at the destination node is lower than the noise threshold, the relay nodes are activated for cooperative data transmission. In order to save node energy, each relay node merely could retransmit once.
In a first stage of cooperative routing: the source node firstly broadcasts to the relay nodes and the destination node.
YSR (f) = XSSR + nSR (YSD(f) = XsSSD + nSD (8)
Underwater acoustic communication is easily affected by a variety of noise sources, such as seabed turbulence, ship motion, waves, turbulence and the like. Considering these factors, the present invention provides a general underwater noise formula as follows:
n(f) = n(f) + nS(f) + nw(f) + nTh(f) (9)
wherein:
10logn,(f) =17 -30 log(f) 10logns(f)=40+20(s-0.5)+26log(f)-60log(f+0,03) 10logn,(f)=50+7.51+20log(f)-40log(f+0.4) (10) 10log nh(f)= -15+20 log(f)
Table 1: Notation for relevant parameters of underwater collaborative routing
Notation Definition
to a YSR(f) signal strength from the source node relay node signal strength from the source node to the YSD(P0 destination node to the signal strength from a relay node YRD destination node original signal strength sent by the source XS node Rayleigh Fading impact factor of channels, YSR/SD/RD _ _ _ _ _ _ _ _ __ E g (0, cV2
) Noise impact function in the course of signal transmission
Signal strength received at the destination YD node Wind Speed (0-10m/s) f Acoustic Communication Frequency s Ship Motion Impact Factor (0 or 1) # Path Loss Factor (2 -4) Transmission Distance between the source dSD node and the destination node, or direct distance Pt Power of data directly sent by nodes Transmission Power from the source node PsDIPn to the destination node/noise power Initial threshold SNR (ratio between signal Yo power and noise power)
In a second stage of cooperative routing: a preliminary determination on the basis of the threshold yo is performed firstly at the destination node, if the transmission signal
received at the destination node is lower than the threshold, the relay nodes are noticed to perform a cooperative retransmission (the selection of the relay nodes is going to be further explained in the following part); at the relay nodes amplification forwarding is being applied to and at the destination node maximum ratio combination is being carried out. The direct transmission signal received at the destination node is expressed as:
YSD F(Sf= 9SD + SD Wf SD
(11)
Complicated channel fading experienced between nodes could be expressed in a form of complex number:
YSD = ISD IejOSD wherein |SSDI is a fading amplitude conforming to the Rayleigh distribution, g E (0,2), 2 = E[lgsD|2] = 1, wherein BSD is a phase, and the power received at the destination node is:
PSD t dSD
(12)
at this time the signal-to-noise ratio (SNR) threshold determination is performed:
PSD SD YD=Pn 1PtS2 _1 =dflD SD Pn dflD SD P"
(13)
wherein P representing a noise power.
If YSD is lower than the initial threshold yo and then cooperative routing is performed, which is expressed as follows:
YRD W = aySR WfSRD + nRDW (4)
YD =YSD Wf+YRD(f (5)
wherein a is the amplification factor and a is set asa= E N Eb is the energy
of the transmitted signal, and No is the power spectral density of the noise.
The complete process of the underwater layered cooperative routing algorithm will be illustrated as follows.
For an underwater self-organizing sensor network, energy consumption is usually an urgent issue. Due to the corrosive nature of seawater the corroded underwater sensor nodes are barely able to be recycled while those sensor nodes in usage are difficult to replace batteries as required. In this regard, the present invention optimizes network energy consumption by establishing an appropriate underwater energy model, in which the underwater routing protocol is required to solve a communication problem caused by a dynamic network topology, also needed to overcome the effect on communication exerted by seawater flow, and demanded to address unstable point-to-point communication between nodes or packet loss because the link quality may affect the entire network performance. Therefore, the present invention provides a layered routing protocol based on cooperation, cooperative routing could improve the accuracy of arriving data packets and layered routing could balance energy consumption. The protocol includes two phases: a layer dividing phase and a transmission phase, wherein the layer dividing phase is configured for network division and node clustering and the transmission phase is responsible for cooperative routing and data forwarding. The two phases are explained in detail below.
The layer dividing phase:
Considering energy balance, the underwater self-organizing sensor network is divided into levels of a same scale. How many layers are divided is calculated by
LN Darea (1)
Wherein LN representing the number of layers, Darea representing a depth range of an area could be monitored by those sensor nodes and W = 2 x r representing a coverage area defined by the transmission radius r of a sensor node. The first layer is defined as a water surface layer in which nodes are not clustered, and directly transmit information to a nearest sink node. Every sensor node is provided with a depth sensor to detect the depth of the sensor node and further to obtain which layer the sensor node is (expressing as a layer serial number), shown as the following formula:
Nnum = mod(LN) (2)
Wherein Nnum representing a serial number of the layer where a sensor node in and Ndpt representing the depth of the sensor node.
The above calculation is repeatedly performed until the layer serial number of every sensor node is obtained and the layer serial numbers of all sensor nodes are stored in a data packet list. At this point, the layer dividing phase is completed.
Next, a process of the selection of a cluster area by an average clustering algorithm and a process of the election of a cluster-head node (CH) by a Bayesian formula will be described at length.
Assuming that in an ideal environment, there are K initial cluster centers in each layer and the total number of nodes is N, then the total number of nodes in each layer is
N 1= N/LN, wherein i c {2,...,LNj.
Ideally, the optimal number of K is defined as:
K = TW
(14)
Wherein W is the transmission diameter of each sensor node and L x L x L is an area range could be monitored by the network.
Taking into account of an uneven distribution of nodes, it is preferably in the present algorithm to select an initial cluster center according to a density of surrounding nodes p (a ratio of the number of nodes located within a circular area with the transmission radius to the total number of nodes). Firstly selecting a node as an initial cluster center K1, and then selecting a node as farther as possible from K1 as a second cluster center K2, and then selecting a node as farther as possible from K1 and from K2 as a third cluster center K3, wherein K3 is a maximum value among min(d(K3, K1), d(K3, K2)), and selecting K4 in a same manner and K4 is a maximum value among min(d(K4,K1),d (K4,K2),d (K4,K3)) repeat the process until all K cluster centers are selected. It should be noted that a cluster area is being selected in each layer according to the same rule until a cluster area is being selected in every layer.
After obtaining K initial clustering centers, an average clustering algorithm is used to cluster the network, where the variance (the sum of squared errors of the cluster areas) is used as a standard metric function, which can be defined as:
E=ZZ X-X (15) i=1 xeR
Wherein x E Ri means that a sending distance of node is within the communication range, X represents a distance between node and sink node and Xi representing depth information of k cluster areas, wherein i G {1,2,...,k}.
A convergence zone is defined as follows:
|E 1 - E 2 1 < E (16)
wherein E representing a minimum value, E1 representing a current measurement function and E 2 representing a previous round measurement function. The standard metric function serves as a criterion to determine whether a cluster area meets a requirement of the convergence zone: if it is not satisfied, the cluster area is congregated again until the condition is met.
Then the election of a cluster-head node by using a Bayesian formula is performed. Firstly calculating an effective time Ht for each sensor node based on the combination of a cluster-head node election time Ti and remaining energy, Ht is obtained by the following formula:
H, = T, + x (17)
Wherein 6[1,0.5] representing any value capable of avoiding nodes having similar remaining energy causing conflicts, Er representing a remaining energy and Er representing an initial energy; and it could be concluded from the formula above that the higher the remaining energy, the shorter the effective time, the higher the probability of being elected as a cluster-head node. A node could be elected as a cluster-head node within the effective time Ht, otherwise automatically gives up competing for the cluster-head node beyond the effective time Ht.
A Bayesian probability is calculated according to remaining energy, energy consumption rate and link quality of every sensor node within the cluster area.
The calculation could result in two cases: a probability of a node being a cluster-head node P (n;=H) and a probability of a node being a cluster member P (n;=H).
Preferably, the present invention calculates a probability of a node being a cluster-head node in the cluster and the maximum of the probability is based on its attribute values.
It could be obtained that a prior probability of a node being elected as a cluster-head node without knowing node attribute values: P(n;=H), a posterior probability of a node being elected as a cluster-head node knowing node attribute values such as remaining energy, energy consumption rate, link quality and the like: P(n=Hx;), wherein xy is the ith attribute value of the it node. Similarly, it could be obtained P(n;=H) , P(n;=H'|x;;) and a probability of node attribute set P(xij), which correspond to the case of a node being a cluster member.
P(xijlni = H) = (P(ni = Hlxij)* P(xjj))/P(nj = H)
(18)
There are only two cases: being H or H'.
P(ni=Hjxii)+P(ni=H'|xii)=1 so that P(ni=H)+P(ni=H)=1.
Assuming that it is known that a node is not a cluster-head node, the posterior probability that the node has a set of possible attribute values is:
.r=H) P(n, = H'|I xPH )* P(x,,) P(xi'xi2,......x In, |i =- H') -[ ni H ]"(19)
[P(n, =H')]j
For facilitate the description, Xi =(xi, x2,..., xia) is the attribute value set of the node. Further the following two formulas can be obtained:
Il=,[1- P(n,=z-H Ix,)] *P(xij) 1-P(n=H) 1 P(nH xz)*P(x) (20)
P(XII ) = j= P(n, =H) x P()(21)
[P(n, =H)a
The attribute value set X is known from the data packet, and the probability of the node being elected as a cluster-head node is:
|n = H)* P(n, = H) P(n,=H|X)=PX,)= P(X (22) P(Xi
) Due to the fact that the attribute value set X is given, the node could be in a H state or in a H'state:
P(Xi) = P(XIjn = H) * P(n = H) + P(XIjn = H)* P(n1 = H) (23)
Therefore, the probabilities of the two states are equal. Based on the above formulas, the probability of a node being elected as a cluster-head node is as follows:
rI = P(n, H | xj) P(nj = H|) H -i) (24) rl"1P(n, = H |x_+ 1P(n, = H | xv.)]
The above formula could be simplified as follows in which Pi is a posterior probability of a node is elected as a cluster-head node and Pi; is a probability of knowing the attributes of the node.
Pi =ry PP-(25) + [-a_]
A reciprocal analysis is being performed on the formula (25) and ll=-Pi; is being eliminated, and a logarithmic analysis is being performed to obtain:
1 1 1n( - 1) = In(J [ 1]) (26)
According to the logarithm property, it could be obtained:
1 1Q ln( -1) = In[-- 1] (27) 8 P.
Therefore, Pi is:
Pln -- (28) e 1 " +1 same as described in formula (3)
wherein Pi is a posterior probability of a node being elected as the cluster-head node, Pi1 is the probability of the jthattribute value of the ith node, and a is the number of attribute value of the nodes; setting a
n = In -1 j=1
,then Pi = e+
The cluster-head node in each cluster area is elected according to the setting probability Pi until the selection in every layer is completed.
The transmission phase:
Since the propagation rate of underwater acoustic signals is much lower than that of radio waves in a acoustic communication network, the underwater propagation delay is greatly increased and data packets may collide in one time slot. Furthermore, the propagation of sound waves in water may create Doppler Effect causing signal distortion failing to be transmitted to a target range. Underwater acoustic channel characteristics have been considered in the present invention wherein preferably the transmitted data is modulated by QPSK (Quadrature Phase Shift Keying) and OFDM (Orthogonal Frequency-division Multiplexing) is used to reduce inter-symbol interference. The focus of the present invention is to improve the transmission in cluster, which is different from the traditional underwater communication by adding into a cooperative routing capable of performing a backup and re-transmission operation on a basis of cooperative communication consisting of source node and relay nodes.
As shown in Fig.3, in the transmission phase, each node obtains its own depth and broadcasts to obtain the depths of other nodes at first, and then stores a nearest node to a neighbor node set of its own (measured by the depth difference between the two nodes). Then relay nodes and destination node are selected. In the prior art merely depths and remaining energy are considered in the selection of relay nodes, if the link quality is lower than a normal standard how to select relay nodes is unclear. It is believed in the present invention that a SNR standard based on signal-to-noise ratio is more reliable in selecting relay nodes.
To be specific, in the present invention, a depth reference dth is being preset which is preferably set as three-fourths of the transmission radius r of a node, sensor nodes with the highest remaining energy which are within a boundary specified by the depth reference dth as candidate relay nodes and sensor nodes with the highest remaining energy which are out of the boundary specified by the depth reference dth as candidate destination nodes.
Taking into depths of nodes, density of surrounding nodes and SNR standard into consideration, suitable relay nodes and destination node could be selected from the candidate relay nodes and the candidate destination nodes as partner nodes, and the partner nodes further perform cooperative routing, and a partner node selection diagram is shown in Fig. 4.
A destination node is being selected in the first, and then a relay-node selection formula is being given by combining a depth difference between the source node and the destination node DSD:
f(VD) = PD x Er/Di (6)
f(VR) = PRxErXi X YSRi/DSD (7)
wherein f(vD) is a formula for selecting the destination node and f(vR) is a formula for selecting the relay nodes.
PD is a destination node density, which is a ratio of the number of nodes covered by the area specified by the transmission radius r and the number of nodes in the layer, is expressed as PD = Nr/Ni; PR is a relay node density, which is a ratio of the number of
nodes covered by an area specified by the depth reference dth, namely r and the
number of nodes covered by the area specified by the transmission radius r and expressed as PR = Ndth/Nr.
The link quality is judged by a SNR standard expressed as:
P 1IF 2 1 P n SR nSSR, (29) iP SA~
After that the relay nodes are selected successfully, the method is set to verify whether or not a direct transmission quality at the destination node satisfies a threshold at first; if the direct transmission quality does not satisfy the threshold, the relay nodes are activated for backup retransmission operation. The intra-cluster nodes communicate with each other cooperatively and the transmitted data is forwarded layer by layer to a final cluster-head node CH, wherein the integration of data is being performed at the destination node before sending a data packet to the cluster-head nodes, so the workload of cluster-head nodes are reduce to only for forwarding the data to water surface; the data is directly sent by node on the water surface to a sink node. Compared with those non-cooperation protocols, the intra-cluster cooperation disclosed by the present invention could ensure the reliability of data transmission and the preprocessing could reduce the workload of cluster-head nodes and network interruption time. Fig. 5 is a flow chart showing the cooperative routing method disclosed by the present invention.
After that a round of data transmission is completed, the cluster-head node (CH) determines a remaining energy of the cluster area where the cluster-head node belonging to according to the remaining energy of other cluster members. If the remaining energy of the cluster area is lower than a network energy threshold, the cluster area in the layer is reconstructed and a new cluster-head node is elected, so the routing information is also updated.
The present invention provides an underwater self-organizing sensor network layered cooperative routing method, in which a relay cooperative model based on cooperative routing is being incorporated in a data transmission phase, accordingly the source node could send out same data through a plurality of paths and the error rate of the data packet received at the destination node is lowered. Compared with a traditional layered protocol, cooperative routing could replace ordinary multi-hop transmission and guarantee the link quality of underwater channels. The average cluster algorithm is used for clustering nodes and the condition probability is used to select cluster-head node. In the course of transmission, the signal is being amplified and backed up in a data packet by the relay nodes so the loss of packet could be avoided so as to improve the data transmission rate and survivability of the underwater self-organizing sensor network; and therefore a solid foundation is being established for the application of underwater self-organizing sensor network to practical seabed observation network.
Another aspect of the present invention provides an underwater self-organizing sensor network layered cooperative routing system.
The underwater self-organizing sensor network layered cooperative routing system includes: cluster-head nodes and intra-cluster nodes; the cluster-head nodes and the intra-cluster nodes are deployed in an underwater self-organizing sensor network; in which a cluster area is selected in each layer and each cluster area contains one cluster-head node and a plurality of intra-cluster nodes; the intra-cluster nodes communicate with each other in cooperation and transmit collected data to corresponding cluster-head node; the cluster-head node integrates data and transmits the integrated data to a cluster-head node in an upper layer, the integrated data is transmitted through cluster-head nodes layer by layer and eventually channel to a node on a water surface layer by a last cluster-head node, and the node on the surface layer forwards data to a nearest sink node on the water surface.
The intra-cluster nodes communicate with each other in cooperation and transmit the collected data to the corresponding cluster-head node. The intra-cluster nodes comprise a source node, relay nodes and a destination node.
The source node broadcasts to the relay nodes and the destination node in the meanwhile and a predetermination is performed at the destination node to evaluate the transmission signal quality by comparing it with a noise threshold.
If the quality of the signal received at the destination node is lower than the noise threshold, the relay nodes are activated for cooperative data transmission.
The above descriptions are only preferred embodiments of the application, and are not used to limit the application. For those skilled in the art, the application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of this application shall be included in the protection scope of this application.

Claims (10)

Claims:
1. An underwater self-organizing network layered cooperative routing method, wherein the method includes:
part of nodes of an underwater self-organizing sensor network are divided into cluster-head nodes and intra-cluster nodes; wherein in one cluster, the intra-cluster nodes communicate with each other in a cooperative manner and transmit collected data to a corresponding cluster-head node; each cluster-head node integrates data and transmits the integrated data to another cluster-head node in an upper layer; data is transmitted through cluster-head nodes layer by layer and eventually channeled to a node on a water surface layer by a last cluster-head node; and the node on the surface layer forwards data to a nearest sink node on the water surface;
wherein the intra-cluster nodes communicate with each other in a cooperative manner and transmit collected data to the corresponding cluster-head node includes: setting the intra-cluster nodes participating in communication respectively as source node, relay node and destination node; the source node broadcasts to relay nodes and a destination node in the meanwhile, and a noise threshold is used to determine the quality of transmission signal at the destination node; if the quality of the transmission signal received at the destination node is lower than the noise threshold, the relay nodes are activated for cooperative data transmission.
2. The underwater self-organizing network layered cooperative routing method according to claim 1, wherein dividing part of nodes of an underwater self-organizing sensor network into cluster-head nodes and intra-cluster nodes comprises:
SI: deploying sensor nodes underwater to form an underwater self-organizing sensor network;
S2: dividing the underwater self-organizing sensor network into a plurality of layers; wherein a layer closest to the water surface is defined as a water surface layer; nodes in the water surface layer are not clustered; and a cluster area is selected in each non-surface layer; a cluster-head node is elected in each cluster area; each cluster area contains one cluster-head node and a plurality of intra-cluster nodes.
3. The underwater self-organizing network layered cooperative routing method according to claim 1, wherein the method further includes: after completing a round of data transmission, each cluster-head node CH determines an average cluster energy according to remaining energy of cluster members; if the average cluster energy determined by one of the cluster-head nodes is less than a network energy threshold, the cluster area of the layer where the cluster-head node in is reconstructed and a new cluster-head node is elected and a routing information is updated.
4. The underwater self-organizing network layered cooperative routing method according to claim 2, wherein the underwater self-organizing sensor network is divided into several layers includes: the underwater self-organizing sensor network is divided into several layers according to a set transmission radius.
5. The underwater self-organizing network layered cooperative routing method according to claim 2, wherein the selection of a cluster area in each non-surface layer includes: selecting a cluster area in each non-surface layer by a clustering algorithm.
6. The underwater self-organizing network layered cooperative routing method according to claim 2, wherein the election of a cluster-head node in each cluster area includes: electing a cluster-head node by using a Bayesian formula.
7. The underwater self-organizing network layered cooperative routing method according to claim 6, wherein the election of a cluster-head node by using a Bayesian formula includes:
S211: Calculating a Bayesian probability according to remaining energy, energy consumption rate and link quality of every sensor node within the cluster area;
S212: a node greater than or equal to the Bayesian probability is regarded as the cluster-head node;
S213: nodes less than the Bayesian probability are regarded as intra-cluster nodes.
8. The underwater self-organizing network layered cooperative routing method according to claim 1, wherein the selection criteria of the relay nodes and the destination node are: in the process of data transmission, each node obtains its own depth information and depth information of other nodes and stores a nearest node to a neighbor node set of its own; the relay nodes and the destination node are selected based on a Signal-Noise-Ratio standard.
9. The underwater self-organizing network layered cooperative routing method according to claim 8, wherein the selection of the relay nodes and the destination node based on the SNR standard includes: presetting a depth reference dth; selecting m sensor nodes with highest remaining energy which are within the boundary specified by the depth reference dth as candidate relay nodes; selecting n sensor nodes with the highest remaining energy which are out of the boundary specified by the depth reference dth as candidate destination nodes; selecting the destination node from the candidate destination nodes; after the selection of the destination node, combining a depth difference between the source node and the destination node, the relay nodes are selected from the candidate relay nodes.
10. An underwater self-organizing network layered cooperative routing system, wherein includes cluster-head nodes and intra-cluster nodes; the cluster-head nodes and the intra-cluster nodes are deployed in an underwater self-organizing sensor network; in which a cluster area is selected in each layer and each cluster area contains one cluster-head node and a plurality of intra-cluster nodes; the intra-cluster nodes communicate with each other in cooperation and transmit collected data to corresponding cluster-head node; the cluster-head node integrates data and transmits the integrated data to a cluster-head node in an upper layer, the integrated data is transmitted through cluster-head nodes layer by layer and eventually channel to a node on a water surface layer by a last cluster-head node, and the node on the surface layer forwards data to a nearest sink node on the water surface; the intra-cluster nodes communicate with each other in cooperation and transmit the collected data to the corresponding cluster-head node; the intra-cluster nodes comprise a source node, relay nodes and a destination node; the source node broadcasts to relay nodes and a destination node in the meanwhile and a predetermination is performed at the destination node to evaluate the transmission signal quality by comparing it with a noise threshold; if the quality of the signal received at the destination node is lower than the noise threshold, the relay nodes are activated for cooperative data transmission that is for backup and retransmission of data packet.
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