LITMIR.BIZ

Скачать книгу

a gateway. PS has a connection to RBS directly or with multiple hops. Communication of two types, intra-WBAN and inter-WBAN occurs in the WBANs. Intra-WBAN is a communication within the sensors of a single WBAN. On the other hand, Inter-WBAN is communication among multiple WBANs. Information collected by the sensors is transmitted to the remote Medical-Server, which is situated in the hospital. Inter-WBAN communication provides dynamic access when patients are doing their normal routine work (during movement in home, office, market or playground). In this case, sensor residing on the human body may or may not be in the range of RBS. So cooperation of multiple WBANs is required for hop-to-hop communion, to reach the RBS. RBS is responsible for further transmission to Medical-Server via the internet. WBANs are capable of protecting human lives by detecting patient’s critical conditions at its early stages. Many human lives are dependent on the performance of the WBAN. Routing strategy is the key to network efficiency. There are different routing mechanisms of inter-BAN and intra-BAN communication. Each WBAN needs to be connected to the external network with the help of a gateway.

This gateway can be a Cellular device, a computer system, or a router which is capable of establishing a connection between inter-WBAN nodes and external internet. The problem arrives when WBAN do not have access to gateway device due to some reason. It is a common experience in a crowded area, like in stadium of international games or any kind of international event, where a huge amount of people access the same network and share their photos and videos. Due to congestion, degradation in the performance of network occurs. Although nowadays cellular networks provide a highly efficient network, it is not enough in some cases, that’s why a separate public safety radio system is used by police, firefighters and emergency medical technicians. It operates in separate portions of the 800 MHz band, which consists of a spectrum at 806–824 MHz paired with spectrum at 851–869 MHz. Another scenario is the battlefield where there is no Access Point available in the vicinity of every soldier as shown in Figure 3.1.

Figure 3.1 Base station is not in access of some WBANs.

      Inter-WBAN communication can be useful in both of the cases. As WBAN consists of low power energy nodes, we required an efficient energy consumption routing technique. Clustering is one of the best solutions for efficient routing, where a cluster head is responsible for the transmission of data of multiple WBANs. Network efficiency is dependent on the cluster’s lifetime. In this paper, we proposed an optimization technique of clusters formation using Evolutionary Algorithms. Each cluster head (CH) is a gateway in between cluster members (PSs) of multiple WBANs and the external network. CHs are selected on the bases of fitness.

3.2 Literature Review

As the patient’s lives are dependent on the data traveling from both inter and intra-BANs network, it needs to be secured. Researchers proposed different techniques, some techniques form clusters among the sensors nodes on a single body, the reason to make these clusters is to efficiently utilize the energy of the nodes in tier 1 transmission. On the other hand, cluster formation in inter-BAN nodes of different WBANs is for efficient hop-to-hop routing for tier 2 transmission. A multi- hop routing protocol is proposed by Sriyanijnana et al., it performs well in the perspective of energy consumption, Packet Delivery Ratio (PDR) and network lifetime [2]. A number of fixed nodes are deployed in the network. A cost function is calculated for or the purpose of selection of Forwarding-node. The defined cost function is based on distance from the coordinator nodes, transmission range, residual energy, and on velocity vector of receiver. With clusters a dual sink approach used by DSCB [3], this clustering mechanism use two sinks. They also used the cost function for the purpose of selection of forwarding nodes. Forwarder node is selected by measuring distance of nodes from sink, its residual energy and transmission power. This clustering mechanism provides better performance in the prospective of network scalability, energy and an end to end delay.

      A Balanced Energy Consumption (BEC) protocol is designed by [4]. In this protocol the relay node is selected with cost function which is based on distance of node form sink. To distribute load uniformly each relay node is selected for a specific round. Nodes nearer to the sink can transmit data immediately to the sink, otherwise data is passed to closest relay node. A threshold value of residual energy is also fixed on meeting the threshold value node only send critical data to sink. A simulation study has shown the better performance in term of network lifetime. Another attempt to achieve better throughput in terms of energy-consumption is achieved in heterogeneous WBAN [5]. It also works on the same principal. Residual energy, data rate and distance from sink, is the basic selection criteria for selection of relay node. Key requirement of any WBAN is minimum delay and energy efficiency. To improve the clustering in WBAN a load balancing and position adaptive technique is proposed by [6]. For the selection of cluster head the author used probability distribution method. A centralized clustering method is proposed by [7] to optimize the consumption of energy in WBAN. The cluster tree based structure is designed for the formation of uniform clusters.

An adaptive routing protocol is deployed by the author in [8]. The channel/link information is used for the purpose of selection of best relay nods for reduction of energy consumption per bit. Sender node only sends the data to sink, by relies on nodes only when the link quality is up to the predefined level of threshold. Otherwise it transmits information to the sink, directly. Omar Smail et al., proposed an energy efficient routing protocol for WBANs [9]. They use residual energy to increase network lifetime. This method used to select energy efficient stable links. In [10] a fuzzy adoptive routing protocol is proposed. It uses clustering mechanism for direct communication with sink node. In decision of forwarding it takes in account the criticality and location. Another routing protocol is proposed by [11] in which routing is managed by mobile-sink, it discovers the shortest route among numerous unequal clusters. This makes sure to avoid the energy hole problem in the network. Results have shown that this clustering technique performed well. A secure cluster base strategy for both inter-WBAN and intra-BAN is purposed by [12]. For intra-WBAN they used to generate a pairwise (PV) key. The best thing about PV is the keys generation on both sending and receiving end is the same. In the result of the highly dynamic nature of the human body, generated PV is time-variant. In inter-BAN communication, clusters are formed on the bases of two parameters (residual energy and distance). The node which has more energy is more likely to form clusters, in the same way, the node that is more closer to the RBS will have a high probability of becoming the cluster head. Some other authors also used genetic algorithms in WBAN [13–16]. A concept of a virtual cluster is given by [17], they form clusters only among intra-BAN nodes. Although nodes in intra-BAN are fairly close to each other, but due to energy limitation in sensors nodes, this technique gave remarkable results.

3.3 Clustering Technique

      By creation of the long-lasting clusters, frequent path search is reduced. We are considering the scenario where multiple WBANs are present. Instead of having a connection of each WBAN with RBS, we considered some of the WBANs are not in the range of RBS. Each WBAN consist of one Personal Server (PS) and multiple sensor nodes. The sensor nodes pass their collected data to the PS and this PS is responsible for further transmission. In our purposed technique PS of different WBANs form clusters. Each cluster contains a cluster head and cluster members (CM) in its vicinity. CH is a selected PS of a WBAN within the WBANs of a cluster. Now all other WBANs will be connected to the CH, multiple CHs of different WBANs can have hop-to-hop communication, and this way data is passed to the nearest AP.

      Our communication can be classified into following hierarchal groups.

       Sensor node to PS

       PS(CM) to CH

       CH to RBS

Figure 3.2

Скачать книгу