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  1. 1. Heena Ahuja, Er. Jyoti Gupta / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 4, July-August 2012, pp.1040-1044 Review of Vector-Based Forwarding Protocol for Underwater Sensor Network Heena Ahuja*, Er. Jyoti Gupta** *Student, Department of ECE, MMU Mullana, Ambala, India ** Assistant Professor, ECE, MMU Mullana, Ambala, IndiaABSTRACT In this paper, we tackle one fundamental latency, node mobility (resulting in high networkproblem in Underwater Sensor Networks (UWSNs): dynamics), high error probability, and three-dimensionalrobust, scalable and energy efficient routing. network topology. These new features bring manyUnderwater Sensor Networks (UWSNs) are challenges to the protocol design of UWSNs. In this paper,significantly different from terrestrial sensor networks we tackle one fundamental problem in UWSNs: robust,in the following aspects: low bandwidth, high latency, scalable, and energy efficient routing. The unique featuresnode mobility, high error probability, and 3- of UWSNs pose great challenges on its routing protocoldimensional space. These new features bring many design and make many existing routing protocols forchallenges to the network protocol design of UWSNs. terrestrial networks unsuitable.In this paper, we propose a novel routing protocol,called vector-based forwarding (VBF), to providerobust, scalable and energy efficient routing. VBF is 1.1 Unique Features of UWSNsessentially a position-based routing approach: nodes UWSNs are significantly different from any terrestrialclose to the “vector" from the source to the destination sensor networks in terms of the following aspects:will forward the message. In this way, only a smallfraction of the nodes are involved in routing. To 1.1.1 Low Bandwidth and High Latency in UWSNs:improve the robustness, packets are forwarded in Acoustic channels (instead of RF channels) are used as theredundant and interleaved paths. Further, a localized communication method since radio does not work well inand distributed self-adaptation algorithm allows the water. The propagation speed of acoustic signals in waternodes to reduce energy consumption by discarding is about 1.5 × 103 m/sec, which is five orders of magnituderedundant packets.VBF performs well in dense lower than the radio propagation speed (3 × 108 m/sec).networks. Moreover, the available bandwidth of underwater acoustic channels is limited and dramatically depends on bothKeywords - Angle of arrival, energy, desirable factor, transmission range and frequency.packets, protocol, self adaptation, vector. 1.1.2 UWSNs Are Highly Dynamic: The underwater1. INTRODUCTION sensor networks we target are highly mobile networks The Earth is a water planet. For decades, there where sensor nodes are not fixed and they will float withhave been significant interests in monitoring aquatic water currents. From empirical observations, underwaterenvironments for scientific exploration, commercial objects may move at the speed of 2-3 knots (or 3–6exploitation and coastline protection. Highly precise, real- kilometers per hour) in a typical underwater condition.time, and temporal spatial continuous aquatic environment This kind of mobility results in a highly dynamic networkmonitoring systems are extremely important for various topology.applications, such as oceanographic data collection,pollution detection, and marine surveillance. However, 1.1.3 UWSNs Are Highly Error-Prone: Underwatertraditional techniques, such as remote telemetry and acoustic communication channels are significantlysequential local sensing, cannot satisfy these high- affected by many factors such as signal attenuation, noise,demanding application requirements. Recently, underwater multipath, Doppler spread, and even water temperature.sensor networks have emerged as a very powerful All these factors cause high bit-error and delay variance.technique for many applications for underwater Thus, communication links in UWSNs are highly error-environment, including monitoring, measurement, prone.surveillance and control [1].Compared with traditionaltechniques in these application scenarios, underwater 1.1.4 UWSNs Are Three-Dimensional: UWSNs aresensor networks enable people to perform underwater usually deployed in a three-dimensional space. This isactivities more accurately and timely in much wider areas. different from the 2-dimensional deployment of most Even though underwater sensor networks terrestrial sensor networks. These characteristics of(UWSNs) share some common properties with terrestrial UWSNs bring up many new challenges and make thesensor networks, such as the large number of nodes and existing routing protocols for terrestrial sensor networksthe limited energy supplies, UWSNs are significantly unsuitable here. For UWSNs, the routing protocols shoulddifferent from terrestrial sensor networks in many aspects: be able to handle the node mobility and the unreliablelow bandwidth, high communication links with high energy efficiency. 1040 | P a g e
  2. 2. Heena Ahuja, Er. Jyoti Gupta / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 4, July-August 2012, pp.1040-10441.2 Routing Challenges in UWSNs relatively stable neighborhood to form the routing path. IfSame as in terrestrial sensor networks, saving energy is a applying these protocols in UWSNs, it would be costly tomajor concern in UWSNs. At the same time, UWSN maintain and recover the frequently broken routing pathrouting should be able to handle node mobility. This due to the node mobility. Geographic routing protocols,requirement makes most existing energy-efficient routing which leverage the position information of each node toprotocols unsuitable for UWSNs. There are many routing determine the forwarding path, have been investigatedprotocols proposed for terrestrial sensor networks, such as extensively for terrestrial wireless networks.Directed Diffusion [2], and TTDD (Two-Tier DataDissemination) [3]. These protocols are mainly designed 2.2 Routing in Underwater Networksfor stationary networks. They usually employ query Much research work has been done in the last few years onflooding as a powerful method to discover data delivery the routing protocols for underwater networks. Thepaths. In UWSNs, however, most sensor nodes are mobile, challenges and state-of-art for the routing protocols inand the “network topology” changes very rapidly even underwater networks have been discussed in detail in [9].with small displacements. The frequent maintenance and A pioneering work is done in on the routing protocol forrecovery of forwarding paths is very expensive in high underwater networks. In this work, a central master nodedynamic networks, and even more expensive in dense 3- is used to probe the network topology and do the routedimensional UWSNs. Thus, to provide scalable and establishment. The authors of [10] propose a centralizedefficient routing in UWSNs, we have to seek for new routing algorithm for delay sensitive application and asolutions. In this paper, we investigate this challenging distributed routing algorithm for delay insensitiverouting problem in UWSNs, with scalability and energy applications in three-dimensional underwater networks. Inefficiency as the design objectives. Moreover, robustness [11], the authors propose a novel method to improve theis also an important concern due to the high node failure efficiency of the flood-based routing protocol inrate and error-prone channels in UWSNs. underwater sensor networks. An adaptive routing protocol for under-water Delay Tolerant Networks (DTN) has been1.2 Contributions proposed in [12], which divides the network into multipleIn this paper, we propose a novel routing protocol, called layers and every node adaptively finds its routes to thevector-based forwarding (VBF), to address the routing upper layer according to its past memory. Different fromproblem in UWSNs. VBF is robust, scalable and energy all the above work, our VBF takes advantages of theefficient. It is essentially a location-based routing location information to form one or multiple routing pipesapproach. No state information is required on the sensor from the source to the destination. Multiple routes mightnodes and only a small fraction of the nodes are involved be used simultaneously in VBF to improve the reliability.in routing. Moreover, in VBF, packets are forwarded along At the same time, the self-adaption algorithm in VBF canredundant and interleaved paths from a source to a greatly improve the energy efficiency. Thus, our VBF candestination, thus VBF is robust against packet loss and achieve a good balance between the reliability and energynode failure. Further, we develop a localized and efficiency. In short, the routing protocols for UWSNs havedistributed self-adaptation algorithm to enhance the to address the node mobility issue at minimum energyperformance of VBF. The self-adaptation algorithm allows expenditure. However, existing routing protocols designednodes to weigh the benefit of for- warding packets and for land-based sensor networks can not satisfy thisthus reduce energy consumption by discarding low benefit requirement. When applied directly in the underwaterpackets. We evaluate the performance of VBF through sensor network environment, these proposals become veryextensive simulations. Our experiment results show that expensive in terms of energy due to node mobility.for networks with small or medium node mobility (1 m/s-3m/s), VBF can effectively achieve the goals of robustness, 3 VECTOR BASED FORWARDINGenergy efficiency, and high success of data delivery. PROTOCOL (VBF)the introduction of the paper should explain the nature of In this section, we present our vector-basedthe problem, previous work, purpose, and the contribution forwarding (VBF) protocol in detail.of the paper. The contents of each section may be providedto understand easily about the paper. 3.1 Overview of VBF In sensor networks, energy constraint is a crucial factor2 RELATED WORK since sensor nodes usually run on battery, and it is In this section, we will review related work in impossible or difficult to recharge them in mostboth terrestrial networks and underwater networks. application scenarios. In underwater sensor networks, in addition to energy saving, the routing algorithms should be2.1 Routing in Terrestrial Wireless Networks able to handle node mobility in an efficient way.Energy efficiency has long been recognized as one of themost important properties for terrestrial wireless networks.Many energy efficient routing protocols such as DirectedDiffusion [4], Two-Tier Data Dissemination [5],GRAdient [6], Rumor routing [7], and SPIN [8], whichaim for high energy efficiency, have been proposed in thelast few years for terrestrial wireless networks. Theseprotocols can achieve high energy efficiency in theterrestrial networks. However, they depend on the 1041 | P a g e
  3. 3. Heena Ahuja, Er. Jyoti Gupta / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 4, July-August 2012, pp.1040-1044 field. The forwarding path is specified by the routing vector from the sender to the target. Each packet also has a RADIUS field, which is a pre-defined threshold used by sensor nodes to determine if they are close enough to the routing vector and eligible for packet forwarding. There are two types of queries. One is location-dependent query. In this case, the sink is interested in some specific area and knows the location of the area. The other type is location independent query, when the sink wants to know some specific type of data regardless of its location. For example, the sink wants to know if there exist abnormal high temperatures in the network. Both of these two types of queries can be routed effectively by VBF. Fig. 1: A high level view of VBF for UWSNs. I) Query Forwarding: For location dependent queries, the sink is interested in some specific area, so it issues an Vector-Based Forwarding (VBF) protocol meets INTEREST query packet, which carries the coordinates ofthese requirements successfully. We assume that each the sink and the target in the sink-based coordinate system,node in VBF knows its position information, which is i.e., it has the information of SP and TP. This query is thenprovided by some location algorithms [13]. If there is no directed to the targeted area following the pipe defined bysuch localization service available, a sensor node can still SP and TP. For a location-independent query, the TP fieldestimate its relative position to the forwarding node by of the INTEREST packet is invalid, and this query will bemeasuring its distance to the forwarder and the angle of flooded to the target nodes. Upon receiving such query,arrival (AOA) and strength of the signal by being armed the intended nodes can compute their locations in the sink-with some hardware device. In this work, we assume that based coordinate system and then direct the subsequentthe position information can be calculated by measuring data packets to the sink.the AOA and strength of the signal. In VBF, each packetcarries the positions of the sender, the target, and the II) Source-Initiated Query: In some applicationforwarder (i.e., the node which transmits this packet). The scenarios, the source can initiate the query process. VBFforwarding path is specified by the routing vector from the also supports such source initiated query. If a sourcesender to the target. Upon receiving a packet, a node senses some events and wants to inform the sink, it firstcomputes its relative position to the forwarder. broadcasts a DATA READY packet. Upon receiving suchRecursively, all the nodes receiving the packet compute packets, each node computes its own position in thetheir positions. If a node determines that it is sufficiently source-based coordinate system, updates the FP field, andclose to the routing vector (e.g., less than a predefined forwards the packet. Once the sink receives this packet, itdistance threshold), it puts its own computed position in calculates its position in the source-based coordinatethe packet and continues forwarding the packet; otherwise, system and transforms the position of the source into itsit simply discards the packet. In this way, all the packet own coordinate system. Then the sink can decide if it isforwarders in the sensor network form a “routing pipe”. interested in such data. If so, it may send out anThe sensor nodes in this pipe are eligible for packet INTEREST packet to the area where the source resides.forwarding, and those which are not close to the routingvector (i.e., the axis of the pipe) do not forward. Fig.1 3.3 Handling Source Mobilityillustrates the basic idea of VBF. In the above figure, node Since the source node keeps moving, its locationS1 is the source, and node S0 is the sink. The routing vector calculated based on the old INTEREST packet might notis specified by S1S0. Data packets are forwarded from S1 to be accurate any more. If no measure is taken to correct theS0. Forwarders along the routing vector form a routing source location, the actual forwarding path might get farpipe with a pre controlled radius (i.e., the distance away from the expected one; that is, the destination of thethreshold, denoted by W in this paper).As we can see, like data forwarding path most probably misses the sink. Weall other source routing protocols, VBF requires no state propose the following sink-assisted approach to solve thisinformation at each node. Therefore, it is scalable to the problem. The source keeps sending packets to the sink,size of the network. Moreover, in VBF, only the nodes and the sink can utilize the source location informationalong the forwarding path (specified by the routing vector) carried in the packets to determine if the source moves outare involved in packet routing, thus saving the energy of of the targeted scope. For example, if the sink calculatesthe network. its position as Pc = (xc, yc, zc) based on the coordinates of the source, Psource = (xsource, ysource, zsource), and its real3.2 The Basic VBF Protocol position is P = (x, y, z), then the sink can calculate the VBF is a source routing protocol. Each packet relative position of the sink to the source as (δx, δy , δz) =carries simple routing information. In a packet, there are (xc -xsource, yc - ysource, zc - zsource).Therefore, the realthree position fields, SP, TP and FP, i.e., the coordinates of position of the source is P’csource = (x - δx, y - δy , z - δz). Bythe sender, the target and the forwarder. In order to handle comparing Psource and P’source, the sink can decide if thenode mobility, each packet contains a RANGE field. source moves out of the scope of the interested area. If so,When a packet reaches the area specified by its TP, this the sink sends the SOURCE DENY packet to the sourcepacket is flooded in an area controlled by the RANGE 1042 | P a g e
  4. 4. Heena Ahuja, Er. Jyoti Gupta / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 4, July-August 2012, pp.1040-1044using P’source. Once the source gets such packets, it stops Fig. 2: Desirableness Factorsending data. At the same time, the sink initia The Algorithm we propose a self-adaptation algorithm3.4 The Self-Adaptation Algorithm based on the concept of desirableness factor. ThisIn the basic VBF protocol, all the nodes close enough to algorithm aims to select the most desirable nodes asthe routing vector are qualified to forward packets. The forwarders. In this algorithm, when a node receives aprotocol is simple and introduces little computation packet, it first determines if it is close enough to theoverhead. However, when sensor nodes are densely routing vector. If yes, the node then holds the packet for adeployed, VBF may involve too many nodes in data time period related to its desirableness factor. In otherforwarding, which in turn increases the energy words, each qualified node delays forwarding the packetconsumption. Thus, it is desirable to adjust the forwarding by a time interval T adaptation, which is calculated aspolicy based on the node density. Due to the mobility of follows:the nodes in the network, it is infeasible to determine the Tadaptation =p × Tdelay + R – d/v0 , (2)global node density. On the other hand, it is inappropriate Where Tdelay is a pre-defined maximum delay, v0 is theto measure the density at the transmission ends (i.e., the propagation speed of acoustic signals in water, i.e.,sender and the target) because of the low propagation 1500m/s, and d is the distance between this node and thespeed of acoustic signals. We propose a self-adaptation forwarder. In the equation, the first term reflects thealgorithm for VBF to allow each node to estimate the waiting time based on the node’s desirableness factor: thedensity in its neighborhood (based on local information) more desirable (i.e., the smaller the desirableness factor),and forward packets adaptively. the less time to wait. The second term represents the additional time needed for all the nodes in the forwarder’s3.4.1 Desirableness Factor: transmission range to receive the acoustic signal from theWe introduce the notion of desirableness factor to measure forwarder. During the delayed time period T adaptation, if athe “suitableness” of a node to forward packets. node receives duplicate packets from n other nodes, thenDefinition 1: Given a routing vector S1S0, where S1 is the this node has to compute its desirableness factors relativesource and S0 is the sink, for forwarder F, the to these nodes, a1, . .. ,an, and the original forwarder, a0. Ifdesirableness factor, a, of a node A, is defined as min (a0, a1, . . . , an) < ac/2n, where c is a pre-defined initiala=p/W + (R−d×cosθ)/R, (1) value of desirableness factor (0< c <3), then this nodewhere p is the projection of A to the routing vector S 1S0, d forwards the packet; otherwise, it discards the packet.is the distance between node A and node F, and is the From Equation 2, we can see that the optimal node doesangle between vector FS0 and vector FA . R is the not defer forwarding packets in the self-adaptationtransmission range and W is the radius of the “routing algorithm. Thus, we have the following lemma.pipe” (i.e., the distance threshold).Fig- 2 depict the various Lemma 1: If there exists an optimal path from the senderparameters used in the definition of desirableness factor. to the target, i.e., each node in the path is the optimal nodeFrom the definition, we see that for any node close enough for its upstream node, then the self-adaptation algorithmto the routing vector, i.e., 0 < p < W, the desirableness selects this path and entails no delay.factor of this node is in the range of [0, 3].For a node, if its desirableness factor is large, it means thateither its projection to the routing vector is large or it is notfar away from the forwarder. In other words, it is notdesirable for this node to continue forwarding the packet.On the other hand, if the desirableness factor of a node is0, then this node is on both the routing vector and the edgeof the transmission range of the forwarder. We call thisnode as the optimal node, and its position as the bestposition. For any forwarder, there is at most one optimalnode and one best position. If the desirableness factor of anode is close to 0, it means this node is close to the bestposition.tes a new INTEREST query and finds a newsource. Fig. 3: VBF with self adaptation An Example we illustrate VBF with self-adaptation in Fig. 3. In this figure, the forwarding path is specified as the routing vector S1S0 from the source S1 to the sink S0. The node F is the current forwarder. There are three nodes namely, A, B and D in its transmission range. Node A has the smallest desirableness factor among these nodes. Therefore, A has the shortest delay time and sends out the packet first. As shown in this figure, node B is most likely to discard the packet because it is in the transmission range of A and it has to re-evaluate the benefit to send the packet. Node D is out of the transmission range of A; therefore, it also forwards the packet. 1043 | P a g e
  5. 5. Heena Ahuja, Er. Jyoti Gupta / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 4, July-August 2012, pp.1040-1044 [3] C. Intanagonwiwat, R.Govindan, and D.Estrin.4. SUMMARY Directed Diffusion: A Scalable and Roust We have described the basic VBF routing Communication Paradigm for Sensor Networks. Inprotocol and the self-adaptation algorithm. We can see that ACM International Conference on Mobile ComputingVBF addresses the mobility of nodes in the network and Networking (MOBICOM’00), Boston,effectively. The positioning of nodes is performed locally Massachusetts, USA, August 2000. [4] C. Intanagonwiwat, R.Govindan, and D. Estrin,and no global synchronization required. VBF has no “Directed diffusion: a scalable and roustrequirement for stable forward path. VBF is an energy communication paradigm for sensor networks,” inefficient and scalable protocol. 1) In VBF, no state Proceedings of the 6th Annual Internationalinformation is required for each node; therefore, it is Conference on Mobile Computing and Networkingscalable to the size of the network; 2) In VBF, only the (MOBICOM ’00), Boston, Mass, USA, August 2000.nodes close to the routing vector are involved in packet [5] F. Ye, H. Luo, J. Cheng, S. Lu, and L. Zhang, “A two-forwarding, and all other nodes are in idle state, thus tier data dissemination model for large-scale wirelesssaving energy. The self-adaptation algorithm helps to sensor networks,” in Proceedings of the 8th Annualfurther reduce energy consumption by selecting more International Conference on Mobile Computing anddesirable nodes.VBF is also robust and less Networking (MOBICOM ’02), Atlanta, Ga, USA,computationally demanding. 1) The success of data September 2002.delivery is not dependent on the stable neighborhood, but [6] F. Ye, G. Zhong, S. Lu, and L. Zhang, “GRAdienton the node density. If there exists at least one path in the broadcast: a robust data delivery protocol for large“routing pipe” specified by the routing vector, then the scale sensor networks,” ACM Wireless Networks, vol.packet can be successfully delivered; 2) The computation 11, no. 3, pp. 285–298, 2005.demand on each node is appropriate for routing on- [7] D. Braginsky and D. Estrin, “Rumor routing algorithmdemand since only simple vector-related calculation is for sensor networks,” in Proceedings of the ACMneeded. International Workshop on Wireless Sensor Networks and Applications(WSNA ’02), pp. 22–31, Atlanta, Ga, USA, September 2002.5. CONCLUSION [8] W. R. Heinzelman, J. Kulik, and H. Balakrishnan, In this paper, we have proposed a vector-based “Adaptive protocols for information dissemination inforwarding (VBF) protocol to address the routing wireless sensor networks,” in Proceedings of the 5thchallenges in UWSNs. VBF is scalable, robust and energy Annual ACM/IEEE International Conferenceefficient: 1) Packets carry routing related information and onMobile Computing and Networking (MOBICOMno state information is required at nodes. Thus, it is ’99), Seattle,Wash, USA, August 1999.scalable in terms of network size; 2) In VBF, only those [9] J. Heidemann, W. Ye, J. Wills, A. Syed, and Y. Li,nodes close to the routing vector are involved in data “Research challenges and applications for underwaterforwarding. Therefore, it is energy efficient. Moreover, sensor networking,” in Proceedongs of the IEEEour self-adaptation algorithm allows a node to estimate its Wireless Communications and Networking Conferenceimportance in its neighbourhood and thus adjust its (WCNC ’06), vol. 1, pp. 228–235, Las Vegas, Nev,forwarding policy to save more energy; 3) VBF utilizes USA, April 2006.path redundancy (controlled by the routing pipe radius) to [10] D. Pompili and T. Melodia, “Three-dimenisional routingprovide robustness against packet loss and node failure. in underwater acoustic sensor networks,” inOur simulation results have demonstrated the promising Proceedings of the 2nd ACM International Workshopperformance of VBF. on Performance Evaluation of Wireless Ad Hoc, Sensor, and Ubiquitous Networks (WASUN ’05), pp. 214–221, Montreal, Calif, USA, October 2005.6. FUTURE WORK [11] A. Goel, A. G. Kannan, I. Katz, and R. Bartos, There are several directions in UWSNs worth “Improving efficiency of a flooding-based routingfuture investigation. 1) In the VBF simulations, we use a protocol for underwater networks,” in Proceedings ofsimple MAC protocol as the underlying link layer the 3rd ACM International Workshop on Underwaterprotocol. This is not a satisfactory choice. Designing an Networks, pp. 91–94, San Francisco, Calif, USA,efficient MAC protocol for underwater sensor networks is September 2008.desirable for the next step. 2) We also plan to study the [12] Z. Guo, G. Colombi, B. Wang, J.-H. Cui, D.reliable data transfer and congestion control problems, Maggiorinit, and G. P. Rossi, “Adaptive routing inwhich are very challenging due to the unique features of underwater delay/disruption tolerant sensor networks,”UWSNs: high end-to-end delay, low bandwidth, and high in Proceedings of the 5th IEEE Annual Conference onerror probability. 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