MDRP: An Energy-Efficient Multi-Disjoint Routing protocol in WSNs for Smart Grids

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#### International Journal on Smart Sensing and Intelligent Systems

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VOLUME 13 , ISSUE 1 (Jan 2020) > List of articles

### MDRP: An Energy-Efficient Multi-Disjoint Routing protocol in WSNs for Smart Grids

Citation Information : International Journal on Smart Sensing and Intelligent Systems. Volume 13, Issue 1, Pages 1-15, DOI: https://doi.org/10.21307/ijssis-2020-016

Received Date : 04-March-2020 / Published Online: 18-August-2020

### ARTICLE

#### ABSTRACT

Rapid increase in sensor electronics has expanded the call for sensor networks in IoT-based devices. Smart grid is a part of IoT framework, which can be used to screen and manage traffic congestion, electricity inﬂuxes, extreme weather, and so on. This is done through a network of transmission lines, smart sensors, and smart meters. It is required to distribute and accumulate information remotely on timely basis from different stages of the grid. The periodic data from the smart meters are transferred to MDMS through WSN’s. In WSN’s, depletion of energy due to unequal load on the sensors is a serious issue, which is to be addressed as it affects the operations of the entire network. To assist these traffic requirements and to boost the network lifetime, asynchronous work sleep cycle approach can be used to create node connections. In this article, an energy-efficient adaptive fuzzy-based multi-disjoint routing protocol in WSN’s for smart grids abbreviated as (MDRP) is proposed, where the next hop node is decided through fuzzy logic. Once the subsequent node is decided, a spanning tree is constructed with the sink node as its root, which calculates the optimal path cost, to transmit the collected data. Furthermore, the simulation results show that the proposed MDRP performs better in terms of network lifetime, packet delivery ratio, total energy consumption, etc.

#### Graphical ABSTRACT

A smart grid is a network that incorporates information and communication techniques with an electric power grid structure to improve the robustness and performance of the power distribution system (Ullah et al., 2017). The Advanced Metering Infrastructure (AMI) is an essential element of the smart grid, and smart meters are basic components of the AMI networks. In the conventional electric grid, recurrent transmission failures, congestion, and electricity theft are few elements that make the electricity grid ineffective in terms of electricity management. These pitfalls are due to unidirectional communication from the power generation to the consumer, whereas in the smart grid the communication is bidirectional (Ghosaland and Conti, 2019). WSN’s can be employed in the AMI networks of the smart grid to monitor, examine, and manage the various operations of the grid. The sensor nodes are restrained in-terms of processing functionality, energy, and memory (Yu et al., 2012). Data collection and aggregation from nodes are to be done timely as it is required to activate load shutdown under maximum usage, demand side management, emergency alerts, etc. Most of the data collection protocols assure the key application requirements such as delay reduction and trust along with energy efficiency. Packet dropping is one of the most important concerns in WSN’s due to the deployment of nodes in harsh environment. Apart from this poor link quality, non-availability of queue at intermediate nodes, improper selection of forwarder node for next hop may be major reasons for packet dropping (Mothku and Rout, 2019). For effective data communication, it is required to select a forwarder node which has a good link quality, high queue size, and good amount of residual energy (Mahmood et al., 2015; Lai et al., 2017). Due to the random deployment of sensor nodes, the routing mechanism ends in hot spot issues and also leads to exclusive density of nodes inside the monitoring area (Zaheeruddin et al., 2017). To cope with these issues and to obtain better performance of the network, researchers have proposed a work sleep cycle scheme for sensor nodes (Alfayez et al., 2015). The work sleep scheme results in opportunistic routing (OR), which facilitates to improve the overall performance of the network. OR allows the nodes within the network to overhear the transmission of the adjacent nodes for data forwarding. The primary characteristic of OR is its potential to transmit the data packet and to synchronize among the relaying nodes (Boukerche and Darehshoorzadeh, 2015). The performance of OR depends on the OR metric, algorithm involved in selection of nodes, and the coordination method used in coordinating the nodes (Biswas and Morris, 2005). The sensor data produced via deploying WSN in AMI networks may additionally have attributes like delay tolerance and sensitivity issues. In smart grids, the monitoring data (e.g. too many Ev’s charging) are delay sensitive as the data have to be communicated with the meter management system in speciﬁed time, while the control data (load shut down) may be considered as delay tolerant with the system requirements of smart grids. Designing an energy proﬁcient routing scheme for the deployed WSN’s in AMI networks faces difficulties like data reliability, deﬁnite delay, node fault, packet drop, delay tolerance, sensitivity issues, etc. (Mahmood et al., 2015; Anees et al., 2019). In conventional routing, the time period for hello messages is ﬁxed which leads to high energy consumption when the hello messages are frequently communicated. A probe message forwarding mechanism is also proposed here for communicating the source information. In this work, the data collection can be initiated by the sink whenever required. Inspired by the work of Yang et al. (2018), the probe message transmitting method is adopted here in the routing process. Once the subsequent forwarder node is selected via fuzzy logic and the source information is analyzed from the probe message, the link connectivity between the adjacent nodes is calculated, which results in the identiﬁcation of opportunistic nodes for connection; hence, a spanning tree can be constructed with the sink node as root and optimal paths can be identiﬁed for data transmission. The following are the contributions in this paper:

1. An energy-efficient routing scheme is proposed which can be used in AMI networks of smart grids.

2. Using the probe message and work sleep scheme opportunistic node, connections are obtained.

3. Considering residual energy, link quality, queue size, and closeness of node to sink a routing parameter has been computed.

4. The performance of the proposed scheme is evaluated through simulation and the results are presented.

## System model

The network and energy model used for routing is discussed in this section. It is assumed the sensor nodes in the AMI network are deployed in random fashion. The nodes are independent, and the AMI gateway is the sink for data collection and monitoring. All the sensor nodes utilizes the work sleep approach to sense and communicate with sink. The nodes can communicate with each other throughout the working mode. Multiple sink strategy is also supported by the network for data collection. A speciﬁc id is allocated to each sink node (Sid). With the help of Sid, multiple sink nodes can be differentiated. Figure 1 describes the work sleep scheme of the sensor nodes deployed in the AMI network. ni, nj, nk are the sensor within their radio range rr, and they operate in asynchronous fashion. Wt indicates the working time, and St indicates the sleeping time. The nodes transmit their data to the adjacent nodes during work mode, i.e. [t1, t2] or [t3, t4]. During work mode, the energy of the nodes starts to dissipate and follows the energy slope progressively. At start, the residual energy is high, and it gradually decreases so it is required to ﬁnd the opportunistic nodes for communication at this stage to gain a better connectivity link. To transmit ‘b’ bits from node ni to nj to a distance ‘d’, the energy required is:

$(1)ETr=E+Empd2(ninj)b.$
(1)

##### Figure 1:

Asynchronous work-sleep cycle approach for nodes in the network.

To receive ‘b’ bits by node nj, the energy required is:

$(2)ERe=Eb,$
(2)where E is per bit energy consumption, and Emp is the energy consumed by the transmission ampliﬁer.

## MDRP protocol for WSN’s in AMI networks

In this section, the energy proﬁcient routing approach is presented. In the proposed data collection scheme, the sink node is stationary and can initiate data collection whenever required. The data collection process includes the following ﬁve phases:

1. Initialization phase.

2. Probe message transmission phase.

3. Subsequent node selection phase.

4. Path estimation phase.

5. Routing phase.

### Initialization phase

Data collection process can be initiated by the sink node randomly whenever required by transmitting a tag message. The tag message includes data collection period and the speciﬁc Sid. Upon receiving the tag message the sensor nodes in the radio range calculate their working time based on their work-sleep schedule. For the network graph creation it is considered that the sink node is always in working mode and any sensor falling within the short radio range can establish communication with the sink at any time and the nodes have the ability to collect the information about their adjacent nodes, status transition between working mode and sleep mode. The distance between the sensor nodes and sink node is computed by the relative signal strength. To reduce the energy consumption EOH metric is used. Expected optimal hops (EOH) is the total number of hops required to transmit the probe message to the sensor nodes. EOH can be computed as:

$(3)EOH=Emp/2E.$
(3)

For the network graph creation, it is considered that sink node remains in a working mode all the time and any sensor node in the network falling within the short radio range can establish communication with the sink at any time and the nodes have the ability to collect the information about their adjacent nodes.

### Probe message transmission phase

When the tag message is received by the sensor nodes from the sink node, the sensor nodes transmit their information to their sink node (i.e. its working time, status transition, source ID, work sleep scheme and their adjacent node id). The format of probe message which is transmitted to sink is shown in Table 1. Sid ﬁeld represents the speciﬁc id of the node that communicates with the sink node. The work sleep scheme represents the period of working and sleeping duration of the respective node. STF is the status transitions of the sensor node, adjacent node id is the available adjacent nodes to the source node. If there is no active adjacent node (node in work mode) or no node is available, the ﬁeld remains empty. Sink id is the identiﬁcation of the sink node that send the tag message, Fid is the ids of the nodes that have already transmitted their probe message to sink. EOH stores the expected hop count required to reach the sink. Tag message is received by all nodes within the radio range and all the nodes can generate probe message. Due to different work sleep scheme and STF of sensor node the efficiency of probe message transmission may decrease. So it is necessary to design a mechanism for forwarding the probe message to avoid unnecessary opportunistic connections and to balance the energy consumption. The process is demonstrated in Figure 2, nr, nm, nt are the nodes that are involved in data transmission. When an intermediate sensor node nm receives a probe message from its adjacent node, it will check the Fid ﬁeld in the table to know the status of the transmitter node, nm. Here, if the node nm has not forwarded the probe message, as indicated in Figure 2A, it updates its own id in the Fid ﬁeld. Based on this, it computes the number of forwarders (NOF) by obtaining EOH value. Then, it computes (EOH–NOF) to ﬁnd an adjacent node with the closest EOH value as optimal forwarder. Unlike if the probe message is forwarded by nm as indicated in Figure 2B, it explores the status of adjacent nodes by checking the Fid ﬁeld. For sake of exposition, if the ids in the Fid ﬁelds are speciﬁed as nn, np, …, nm, nr, ns. The node nm explores table to learn about the nodes that have already transmitted the probe message. In this case, the node updates the Fid by deleting the ids of nm, nr and includes its speciﬁc id, followed by the calculation of NOF (EOH–NOF) and ﬁnds the optimal forwarder. Here, the nodes follow asynchronous work sleep scheme, node nt can transmit the probe message to nm only if nt is in work mode as indicated in Figure 2C. If the node is in sleep mode as indicated in Figure 2D, the node stops transmitting. Figure 3 describes the mechanism of probe message transmission.

##### Table 1.

The design of the probe message.

##### Figure 2:

Illustration of probe message transmission.

##### Figure 3:

Probe message transmission.

### Subsequent node selection phase

Fuzzy-based subsequent node selection for routing in AMI networks is discussed in this section. Upon receiving the probe message, the sink node initiates data collection process by constructing a random graph with sink as its root. In this work, the subsequent node for data transmission is chosen by fuzzy logic, to choose the subsequent node for transmission Node’s residual Energy (NRE), Link quality (LQ), Queue size (QS) and Status transition frequency (STF) are considered. Every node in the network must ﬁnd a fuzzy output value to its adjacent node based on the input parameters. Upon calculating the fuzzy output value, the subsequent node for hopping is chosen.

### Fuzzy inputs and fuzziﬁcation

The formation of the network graph depends on the work sleep cycle of the nodes and also on the probe message information obtained during the initialization phase. NRE, LQ, QS, STF are the fuzzy inputs considered here. The I/O variables make the use of the triangular membership function to signify the linguistic terms. The mapping between the input space (universe of discourse) and the membership value is described by the membership function. The nodes energy is computed with the help of Equations (1) and (2). The relationship between the input output variables with the corresponding linguistic terms is shown in Table 2. Fuzzy rules are established using a heuristic approach which is based on the following axiom. The subsequent node for hopping is selected based on high energy, available queue size, high status transition frequency, and good link quality. The default rules and membership function guide to obtain the fuzzy output variable. Figure 4A-D describes the fuzzy inputs and their corresponding input linguistic terms used here and Figure 5 describes the fuzzy output variable.

##### Table 2.

Fuzzy I/O variables and their linguistic terms.

##### Figure 4:

Membership functions for input variables.

##### Figure 5:

Membership function for output variables.

The obtained fuzzy variable as output will be converted to a single crisp value which signiﬁes the chance for becoming next node for hopping. The fuzzy output variable is obtained by the default rules and membership function used. In general, the fuzzy logic system consists of four modules fuzzifer, rule set, inference engine, and defuzziﬁer. In the fuzziﬁer, the crisp input parameters µ(NRE, LQ, QS, STF) and their linguistic levels are determined. Table 2 describes mapping between I/O variables and their corresponding linguistic variables.

The rule set comprises a set of if-then rules that are generated through the Mamdani approach. The set of rules are presented in Table 3. Inference engine infers the output with the help of if-then rules. Defuzziﬁer converts the fuzziﬁed value into a crisp output value which signiﬁes the chance of become next node for hopping. The centroid technique is used in the defuzziﬁcation process. The default rules and membership function guides to obtain the fuzzy output variable. The process of subsequent node selection is described with help of Figure 6.

##### Table 3.

Fuzzy decision rules.

##### Figure 6:

Subsequent hop node selection.

### Optimal path estimation

In the proposed algorithm, the subsequent node for routing is chosen using fuzzy logic. Once the subsequent node is known, data collection process is initiated by construction of spanning tree. With help of this, the optimal multi-disjoint paths under traffic considerations toward the sink can be computed. To create the tree structure, it is presumed that the sink node is always active and the sensor nodes located within the radio range rs can establish communication with the sink. The tree is created based on a data set which comprises of source node (SN), its adjacent nodes (AN), work sleep cycle routine (W/S), status transition frequency (STF), nodes remaining energy (NE) and its queue size (QS) and chosen subsequent node (SBN). With the help of the dataset D(SN, AN, W/S, STF, NE, QS, SBN) communication can be established with the gateway (sink node) by the sensor nodes. Once the next node for communication is decided by the fuzzy logic, the optimal paths is to be calculated between sensor nodes and the sink node. Path connectivity (PC) depends on the link connection between the adjacent nodes which is calculated from the following equation 4:

$(4)PCpath(ni,ni+k,k)=∏j=0k−1Pni+jni(j+1)$
(4)where ni represents the source node, ni+k represents the node that is in distance of k hops from node ni on this path. While constructing the spanning tree to calculate the optimal paths of intermediate and distant nodes, the adjacent nodes to the sink can be utilized as their paths are already created. The sink node computes the path connectivity with the sensor nodes as:
$(5)Path(nsink,ni,*)={nnsink,ni,ifnsinkislinkeddirectlytonϕ,otherwise.$
(5)

The updated path connectivity values from intermediate and distant nodes is obtained by the sink node. In each round of communication, the sink node compares the new PC values with the earlier PC values to choose the maximum PC value. The process is repeated until the sink receives the information from all nodes:

$(6)PCupdatenj=max[PCnsinknj,PCnsinkniX∏j=0k−1Pni+jni(j+1)].$
(6)

If PC is updated then:

$(7)Pathnsink,nj,*=Path(nsink,ni,*)+nj.$
(7)

Once the spanning tree is formed the sink broadcasts to the nodes that lie in the long radio range (rl) during each round of communication. If any node is not part of this spanning tree, it waits for the next tag message from the sink. It waits for the next tag message from the sink. On receiving the tag message, the node re-sends its probe message, and the sink node will choose new hop nodes, reconstruct the spanning tree and will recalculate the optimal path.

### Multi-disjoint path for routing

Once the spanning tree is formed, the routing scheme is to be deﬁned. The optimal path on the spanning tree is the appropriate path to route the sensed data to sink node. The conventional opportunistic routing just incorporates the asynchronous work sleep cycle of the sensor nodes leading to link failure if any forwarder node in the network is in the sleep state. Also, it doesn’t support the different data constraints of the smart grids, so an alternate multidis-joint path opportunistic routing is required to adapt the nodes different operating status for a reliable data transmission. If a node ni wants to transmit the sensed data to the sink and if the node ni is far away from the sink node, then an intermediate node nj receives it. Node nj will try to communicate with its immediate neighbor nk if it is in working mode. If the node nk is in sleep state, then the node nj must choose another node for data forwarding. For each immediate neighbor node ni of nj on the spanning tree, the link connection between the nodes is to be calculated using Equation (7) to ﬁnd the path cost. The process of a data forwarding from source node to its sink is depicted in Figure 7.

##### Figure 7:

Multi disjoint path selection for data communication on the spanning tree.

Whenever the node ni wants to communicate with the sink node, it forwards the data to its immediate neighbor nj and node nj forwards it to node n1 and n7. Both n1 and n7 are in the working state in the spanning tree. So there are two paths available for data communication ni-nj-n7-n8-n9-n10-n11-sink and ni-nj-n1-n2-n3-n4-n5-n6-sink. The node n1 computes the link connectivity Pn1n7 and Pn1n2 from the stored pc values in n1 and compute Pn1n2 × PCpath (n2, nsink,*) and also Pn1n7 × PCpath(n7, nsink,*) to get the PC of the corresponding paths. As the PC of Pn1n2 × PCpath(n2,nsink,*) is greater than the other, this path is chosen for data communication.

## Results and discussion

### Simulation environment

In general, the AMI networks are deployed as static multi-hop networks. The sensor nodes are assumed to be autonomous and alike with communication range of 20 m. The various simulation attributes are described in Table 4. The performance of the MDRP protocol is evaluated with help of Matlab and compared with few other routing protocols like POFA (Chang et al., 2012), DCBONC (Yang et al., 2018), and EXOR (Biswas and Morris, 2005).

##### Table 4.

Simulation attributes.

### Energy consumption

It is the total energy consumed by nodes to the total number of sensor nodes deployed in the network ratio. The energy level of the network is proportional to the network life span, so this parameter is important. The network life span prolongs with a lesser energy consumption ratio.

From Figure 8, it is obvious that as the number of nodes increases the energy consumed by the nodes in the network also increases. Figure 9 illustrates with increase in radio range the number of hops also increases. It is obvious the number of hops in POFA is large compared to other protocols. In the proposed MDRP protocol with the expansion of the radio range, the network density remains unchanged whereas if the distance between the source and sink increases it may affect the success rate of data transmission. It can also be noted that MDRP performs better than DCBONC as the subsequent node for data communication is calculated through fuzzy logic which helps the nodes to save their energy as the radio range increases. The nodes consume slightly more energy in the proposed MDRP protocol when compared with EXOR and much lesser when compared to POFA. In POFA with increase in network density, the energy consumed by the nodes also increases. This is due to the fact, as network density increases, it selects multiple data forwarders which, in turn, increases the number of hops resulting in more energy consumption. It consumes lightly higher energy when compared to EXOR because MDRP uses asynchronous work sleep strategy for data communication. When the adjacent node is in the sleep state, the node involves in various process like path calculation and selection, fuzziﬁcation, etc., which results in energy consumption. It performs better than DCBONC because in MDRP the process of subsequent node selection is not done separately which helps in Energy saving.

##### Figure 8:

Energy consumed by nodes in the network.

##### Figure 9:

Hop count variation with increase in radio range.

Figure 10 illustrates that energy consumed by the nodes increases with time. Energy consumption is the energy consumed by the nodes during data transmission regardless of the status of data delivery. EXOR consumes 95% more energy, POFA consumes 260% more energy, whereas DCBONC consumes 55% more energy when compared with the proposed MDRP protocol. The maximum energy consumption in MDRP protocol is during the probe message forwarding and data transfer. The EOH metric, subsequent nodes selection and the path cost calculation by the sink helps in decreasing the energy consumption in the network.

##### Figure 10:

Energy consumed vs network simulation time.

### Packet delivery ratio

It is the ratio of packets received by the sink node to number of packets transmitted by the sensor nodes. When the data packet is forwarded to the adjacent nodes during working state, it is considered as successful packet transmission and it is unsuccessful (packet drop) when a particular node doesn’t ﬁnd or have any active adjacent nodes (i.e. the node may be in sleeping mode or at transition mode). PDR is evaluated with respect to the radio range in this case. Figure 11 illustrates that PDR in POFA increases with radio range, whereas in other protocols like DCBONC, EXOR, and MDRP the PDR decreases with radio range. In POFA, as the radio range increases, more nodes are involved in data collection increasing the number of hops for data communication which reduces the efficiency in data delivery, whereas in the proposed MDRP protocol, EXOR and DCBONC PDR decrease with increase in radio range. Figure 11 shows that the proposed MDRP protocol performs better in terms of PDR. The proposed MDRP protocol achieves 135%, 60.26%, and 30% over POFA, EXOR, and DCBONC.

##### Figure 11:

Packet delivery ratio.

It is one of the most signiﬁcant criteria to assess the network performance. By measuring the number of dead nodes, network lifetime can be estimated. The network lifetime can be computed from the energy drained by 25% of nodes in the network. From Figure 12, it can be observed that with increase in time the nodes death rate also increases. In this simulation, the data collection period is 600 seconds and the data collection process can be initiated randomly within the network. The nodes die faster in the case of POFA when compared to DCBONC EXOR and MDRP. It can be observed from Figure 12 that MDRP performs better than all schemes. This is due to the selection of proper node as next hop node through fuzzy logic and the calculation of optimal paths for the subsequent forwarders in the network. It can also be observed that MDRP performs better than DCBONC. This is due to the proper selection of next hop node. DCBONC uses time frequency parameter to estimate the optimal paths for communication, whereas MDRP uses buffer size link quality and nodes residual energy to attain better network performance.

### Average end to end delay

One of the important parameters to evaluate the performance of energy efficiency in QoS routing protocols is average end to end delay. In this simulation, the average packet delay is considered. Figure 13 illustrates the average packet delay with respect to the packet receiving rate for various protocols discussed in this paper. Here, the change in delay is measured against the rate of packet arrival. MDRP performs better than other protocols due to the queuing model usage in the AMI environment of smart grids. DCBONC don’t differentiate between the traffic types which results in a slightly lower average packet delay. MDRP performs better as it calculates the link and path connectivity for data transmission.

##### Figure 13:

Avg end to end delay.

## Conclusion and future work

An energy Efficient adaptive fuzzy-based multi-disjoint routing protocol is proposed for WSN’s which can be employed in the AMI networks of SG. In the proposed MDRP protocol, the sink node can initiate a data collection randomly whenever required by broadcasting a tag message. Upon receiving the tag message, the sensor nodes formulate their work sleep schedule and the probe message is transmitted to the sink as an acknowledgment. The probe message has information about the source node, work sleep agenda, status transition frequency of the nodes and subsequent node for data transmission. When the probe message is received, the sink node constructs a spanning tree with sink as root. Then, it calculates the path connectivity cost (PC) to ﬁnd the optimal path for each sensor node. Based on these factors, a routing protocol is proposed that adapts with the operating status of the node.

The possible future work could be integrating this scheme to cognitive radio sensor networks for handling predictive channel assignments. Also, the scheme can be implemented with model predictive controllers for predicting the changes in the demand side management, real-time traffic issues like faults, blackouts, power surges, etc., in smart grids.

### FIGURES & TABLES

Figure 1:

Asynchronous work-sleep cycle approach for nodes in the network.

Figure 2:

Illustration of probe message transmission.

Figure 3:

Probe message transmission.

Figure 4:

Membership functions for input variables.

Figure 5:

Membership function for output variables.

Figure 6:

Subsequent hop node selection.

Figure 7:

Multi disjoint path selection for data communication on the spanning tree.

Figure 8:

Energy consumed by nodes in the network.

Figure 9:

Hop count variation with increase in radio range.

Figure 10:

Energy consumed vs network simulation time.

Figure 11:

Packet delivery ratio.

Figure 12: