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IEEE COMMUNICATIONS LETTERS, VOL. 15, NO. 11, NOVEMBER 2011
A Reliable Route Selection Scheme Based on Caution Zone and Nodes’ Arrival Angle D. G. Reina, Student Member, IEEE, S. L. Toral, Senior Member, IEEE, P. Jonhson, Member, IEEE, and F. Barrero, Senior Member, IEEE
Abstract—A route selection scheme based on RSS is proposed to improve the reliability of MANETs in terms of packet delivery ratio and the usage of routing packets. The proposed approach estimates the node’s arrival angle using RSS variations to obtain route’s lifetime and to decide about the convenience of a neighboring node. Obtained results outperform other approaches using RSS, which does not take into consideration nodes’ mobility. Index Terms—Routing protocols, MANETs, RSS, reliability.
I. I NTRODUCTION HE Mobile Ad Hoc Networks (MANETs) are wireless networks which are deployed without the need for an infrastructure. Therefore, their routing protocols are responsible for deciding how the information is going to move through the network. One of the most important elements of these routing protocols is route selection, since nodes are intrinsically mobile and consequently, routes between nodes suffer from changes. Whenever a topological change occurs in the network, the routing protocols should react either repairing the route or finding an alternative to reach the destination. In general, long-life routes are preferred to short-life ones as routing protocols use routing messages to repair the broken communication paths causing overheads in the network and more energy consumption [1]. Routes’ lifetimes depend on the distance among the nodes, which can be estimated using RSS (Received Signal Strength) [2]. When noisy environments are taken into consideration, RSS is also used to calculate the Signal- to Noise Ratio (SNR), and to estimate link quality. In [3] the authors categorized nodes as either good or bad neighbors using the measured SNR value. Although a poor SNR value can lead to a broken link, the △𝑆𝑁 𝑅 provides more relevant information because it is related to the nodes’ movements. More specifically, a △𝑆𝑁 𝑅 > 0 means that, (1) nodes are getting closer, or (2) nodes are moving toward a location with less interference. In contrast, a △𝑆𝑁 𝑅 < 0 means that, (1) nodes are moving away, or (2) nodes are getting into noisier locations. In [4] the RSS value was used to calculate the link available time (LAT) between two mobile nodes. Though the results achieved were satisfactory, they are valid only for certain nodes’ directions (radial movements towards the target node), which do not cover all the movement possibilities within the covered area (i.e. tangential directions). Moreover the assumption of calculating RSS proportional to
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Manuscript received July 14, 2011. The associate editor coordinating the review of this letter and approving it for publication was I.-R. Chen. D. G. Reina, S. L. Toral, and F. Barrero are with Escuela Superior de Ingenieros. Avda. Camino de los Descubrimientos, University of Seville, s/n 41092 Sevilla, Spain (e-mail:
[email protected]). P. Jonhson is with Liverpool John Moores University, England. Digital Object Identifier 10.1109/LCOMM.2011.082911.111539
𝐷𝑖,𝑗 (𝑡)−2 , where 𝐷𝑖,𝑗 is the distance between the nodes i and j, is only valid whenever the free space propagation model is used, which it is not always a suitable assumption for ad hoc networks. In this letter a cross-layer design in which the physical layer collaborates with the routing layer by providing the RSS value is proposed to improve the reliability of route selection and, as a consequence the path duration in ad hoc networks. As a difference to previous works, this letter goes further in the use of RSS by estimating the node’s arrival angle as function of △𝑅𝑆𝑆 and nodes’ speeds. To demonstrate the validity of this approach, it has been implemented over Ad Hoc On Demand Distance Vector (AODV) routing protocol using the network simulator 2 (ns-2). II. P ROPOSED A PPROACH The proposed approach consists of using △𝑅𝑆𝑆 and nodes’ speeds in order to determine the stability of a communication route between two nodes. The △𝑅𝑆𝑆 is calculated as 𝑅𝑆𝑆𝑡2 − 𝑅𝑆𝑆𝑡1 (1) △𝑅𝑆𝑆 = 𝑡2 − 𝑡1 By using △𝑅𝑆𝑆, it is possible to calculate the node’s arrival angle at which a neighboring node enters the coverage area of a target node. A calibration procedure has been carried out to estimate the limiting △𝑅𝑆𝑆 equivalent to the mentioned critical arrival angle for each considered node’s speed. An alternative to RSS would be the use of a Global Positioning System (GPS), calculating the arrival angle by using the node’s coordinates in two consecutive measurements. The node’s arrival angle and the relative speeds between the nodes both determine the lifetime of their communication link. However, a bordering node is more likely to get out of the node’s coverage area and, consequently, more likely to break an established route. For this reason, a border caution zone and an inner stable zone have been defined, as illustrated in Fig. 1. The critical angle 𝜃𝑐 is defined as the arrival angle so that when a neighboring node arrives at this angle, it remains in the caution zone without getting into the stable zone. A metric has been defined in order to determine the quality of the neighboring nodes considering the estimated arrival angle. This metric has been included in the request packet (RREQ). The proposed link metric ranges from 2 to -2 (the meaning of the metric is explained below). In addition, a path metric related to the quality of the whole path is introduced. The path metric is defined as the minimum link metric along the path. The proposed approach solves the problem of short-life routes as follows ∙ Whenever a neighboring node enters the caution zone with an arrival angle 𝜆 lower than the critical angle
c 2011 IEEE 1089-7798/11$25.00 ⃝
REINA et al.: A RELIABLE ROUTE SELECTION SCHEME BASED ON CAUTION ZONE AND NODES’ ARRIVAL ANGLE
Fig. 1.
Possible node’s locations and directions.
Fig. 2.
AODV with caution zone.
Fig. 3.
AODV with caution zone and critical angle.
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𝜃𝑐 , it will be considered as part of a possible route, as illustrated by node B in Fig. 1. The metric of this link is 1. ∙
∙
∙
Whenever a neighboring node enters the caution zone with an angle 𝜆 equal or higher than the critical angle 𝜃𝑐 , it will be considered as a bad neighbor and consequently it will not be considered in the creation of new routes, (see node D in Fig. 1). The metric of this link is set to -1. If a neighboring node leaves the stable zone, it will be considered as a bad neighbor, as happens with node C in Fig. 1. The link’s metric in this case is -2, which is the lowest metric. Finally, if the neighboring node is located in the stable zone the link metric will be 2, which is the best possible metric. It is the case of node E in Fig. 1.
The Fig. 2 and Fig. 3 show the discovery procedures for AODV with a caution zone and the proposed approach, respectively. In the proposed approach, the path metric is updated every time the request packet is forwarded. Moreover, the intended approach generates a new reply packet (RREP) if a better path is found, Fig. 3. In contrast, in AODV only the first RREQ is responded. As a consequence, the probability of finding a good route is much lower in AODV. Furthermore the RREQ packets with a metric lower than 0 are not forwarded. Consequently, the number of useless RREQ is notably reduced, improving as a result the total routing load. III. P ERFORMANCE E VALUATION The proposed routing scheme has been implemented over AODV using ns-2. The waypoint mobility model [5] has been used. In this model, a node moves from its current position to a new position by selecting a random direction and a random speed. Each node will have a different allocated speed from its neighbors. A node will be allocated with a random speed in a range of 1 to 30 m/s. Whenever the node reaches its destination, it stops for the duration of a ‘pause time’ and chooses a new destination point. The ‘pause time’ for mobile
sensors has been fixed to 0 s, which means all nodes are always moving during the entire simulation period. Also, in this simulation the Two-ray propagation model has been used. A simulation area of 1000 x 1000 m and a node’s coverage area of 250 m have been considered. The radius of the stable zone is 𝑟 = 195 m being equivalent to an RSS value of -60 dBm, using the default values of ns-2 related to the power transmission and the Two-ray propagation model. The critical angle 𝜃𝑐 is 80𝑜 . The duration of the simulation is 1000 s with a warm-up period of 100 s. The number of connections among nodes is 30, starting at random times during the warm up period. The used traffic is constant bit rate (CBR) with a packet size of 512 bytes, and a packet rate of 4pck/s. The number of nodes in the network is varied from 30 to 60 nodes in steps of 5, and the nodes’ initial positions are chosen randomly. The proposed approach AODV with critical angle (AODV_CA) has been compared with AODV, AODV with fixed caution zone (AODV_CZ) [3] which considers RSS but without taking into account node’s mobility, and AODV-LAT [4] which guarantees a minimum link lifetime. The caution zone for AODV_CZ is limited by
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IEEE COMMUNICATIONS LETTERS, VOL. 15, NO. 11, NOVEMBER 2011
Fig. 5.
Fig. 4.
Network performance metrics.
𝑟 = 195𝑚, and 𝐿𝐴𝑇 = 20𝑠 for AODV_LAT. The simulation results have been obtained for two groups of metrics, (1) network performance as given in Fig. 4, and (2) path duration as given in Fig. 5. Each point in the following graphs has been calculated by averaging the results of five different simulations, each with different initial nodes’ positions and nodes’ mobility. In addition, an analysis of variance has been done, in which significant differences among means were obtained. The group (1) is composed of packet delivery fraction (PDF) Fig. 4 (a), throughput Fig. 4 (b), and normalized routing load (NRL) Fig. 4 (c). On other hand, path metric group is composed of the number of error packets and time between error packets (TBE). Since the error packets (RRER) are sent whenever a broken link occurs, they can be considered as the key metrics to determine the lifetime of routes in AODV. The simulation results for the network performance show that the use of a
Path duration metrics.
caution zone improves the network performance compared to that of AODV and AODV_LAT. However, the performance of the proposed AODV_CA outperforms that of AODV_CZ, when the number of nodes is higher than 40 Fig. 4 (a) and (b). The reason for this is the probability of finding a better route increases with the proposed approach as the number of nodes gets higher. The proposed approach discards bordering nodes which are getting away and tangential nodes which are useless in order to form new routes with better suited neighbors. Consequently, only good neighbors are selected always, even if they are located in the caution zone. The result is that selected routes are more reliable and cause less breakage of routes. Simulation results also show that the NRL for the proposed approach is reduced compared to the other approaches, Fig. 4 (c). This reduction is explained by three reasons (1) the number of useless RREQ is reduced, (2) the number of RREQ packets used to recover from broken paths are also reduced, and (3) the number of RRER packets is significantly lower, Fig. 5 (a). The reduction of NRL is of vital importance since the routing load is the main cause of overhead in wireless networks. Moreover, this reduction helps to save power consumption which is one of the critical parameters in the design of ad hoc networks. The results of AODV_LAT demonstrate the importance of considering the nodes’ relative angle to estimate LAT properly. For the same reasons, finally the frequency of broken
REINA et al.: A RELIABLE ROUTE SELECTION SCHEME BASED ON CAUTION ZONE AND NODES’ ARRIVAL ANGLE
path has been also reduced in the proposed approach when compared to the rest of the approaches, as shown in Fig. 5 (b). IV. C ONCLUSION A reliable route selection scheme based on RSS and nodes’ arrival angle has been presented in this letter with the objective of reducing the number of broken routes and thus improving the network performance. The simulation results obtained for various scenarios considering a variable number of nodes and changes in the nodes’ mobility have shown that the proposed approach (AODV_CA) outperforms that of the existing protocols by a huge margin. The proposed approach can also be implemented over any other reactive or proactive routing protocols such as Dynamic Source Routing (DSR), or the Destination Sequence Distance Vector (DSDV).
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