Dead-Zone Avoidance Algorithm for Location Based ...

Dead-Zone Avoidance Algorithm for Location Based Routing Protocols Said Ghoniemy

Amal Elnahas

Omar Karam

Ihab El Kabary

Faculty of Computer & Information Sciences, Ain Shams University

Faculty of Media Engineering & Technology, German University in Cairo

Faculty of Computer & Information Sciences, Ain Shams University

Faculty of Computer & Information Sciences, Ain Shams University

[email protected]

[email protected]

[email protected]

[email protected]

Abstract: An ad hoc network is a network with a continuously changing topology where nodes may be connected or disconnected based on their transmission range and that of their neighbors. In this paper we propose an algorithm that gives each node a warning prior moving into a Dead-Zone or a clearance if it's moving toward a Zone reachable by other nodes in the ad hoc network. We achieve this by creating a Dead-Zone Avoidance Compass (DZAC) for each node based upon the position of it's neighboring nodes using positional information obtained from Global Positioning Systems (GPS) receivers [1,2,3]. Our performance evaluation showed that the Location-Aided Routing protocol aided with the Dead-Zone avoidance algorithm (DZA-LAR) performed better than Dynamic Source Routing (DSR) and Location-Aided Routing (LAR) protocols in terms of data packet delivery ratio but with an increase in network overhead. Keywords: Mobile Communications, Ad hoc Networks, Routing Protocols, Location Based Routing, Location-Aided Routing Protocol

1 Introduction An ad hoc network is a collection of wireless mobile nodes forming a temporary network without the aid of any established infrastructure or centralized administration. Due to limited transmission range of each node, every node in the ad hoc network isn't aware of the complete topology of the whole network, multiple hops maybe needed for one to exchange data with another node not in its direct transmission range. But a node may move into a place where no other node is in its direct transmission range. It will not be able to communicate with any other node in the ad hoc network until it moves back into direct transmission range of one or more of the nodes in the ad hoc network. The use of Ad hoc networks becomes a necessity when we need to achieve communication in an area where no fixed communication infrastructure is available or where this fixed communication infrastructure will be very expensive to establish in terms of time or money constraints like in battlefield applications or in emergency relief operations. Various routing protocols have been developed to facilitate the communication between nodes in an ad hoc network taking into account the dynamic behavior of these nodes. These routing protocols are built assuming that each node acts as both router and host simultaneously. In other words if a source node S needs to send information to a destination node D it can do so directly if D is in direct transmission * range of S or through intermediate nodes between S & D that can act as routers of these information.

Fig.1. Source Node S is sending information to destination Node D, which is not in its direct transmission range, through intermediate nodes A & B

Fig.2. Source Node S is trying to send information to Destination Node D in vain since Source Node D is in a Dead-Zone

Consider the case were a node in the ad hoc network moves to a position where there isn't another node in its direct transmission range. This implies that this node is no longer a member of the ad hoc network since it is unreachable by any other node and it can't send information to any node. In other words we say that this node has entered a Dead-Zone. It's worth mentioning that node D can move into a Dead-Zone without receiving any warning prior to that movement simply because it lacks the positional information of its neighboring nodes.

*

We define transmission range as the threshold distance to where a received signal has a 10 dB signal to noise ratio.

In this paper we develop an Algorithm that uses positional information from the GPS receivers attached to each node in the ad hoc network to create a Dead-Zone Avoidance Compass (DZAC). This DZAC provides each moving mobile node with the directions in which it can move freely within the ad hoc network and warns it of directions possibly leading into a Dead-Zone. The DZAC can also be used to help the node backtrack and move into areas covered by the ad hoc network in case the node already moved into a Dead-Zone using the latest data the DZAC obtained just before it moved into a DeadZone. The rest of this paper is organized as follows. In the next section, we present a detailed explanation on how the proposed algorithm operates, followed by a demonstration of the applicability of the algorithm with Location-Based Routing protocols then we outline the design considerations we took into account when designing the algorithm. Section 3 evaluates the performance of the DZA-LAR in comparison with DSR and LAR protocols in various network conditions. We summarize our contributions and observations in Section 4.

2 The Dead-Zone Avoidance Algorithm In order to guide a mobile node that is always on the move and assist it to avoid entering a Dead-Zone, we need to have up-to-date positional information from the neighboring nodes. This positional information is in the form of X, Y coordinates obtained by a GPS receivers attached to each node. Current GPS receivers provides accurate three-dimensional position (latitude, longitude, and altitude), velocity, and precise time traceable to Coordinated Universal Time(UTC). In our implementation of the algorithm, we will neglect the effect of the Earths curvature assuming that the transmission range of the nodes in the network must be greater than the maximum line-of-sight distance d LOS which is equal to 2

2hR + h 2 where h is the height of both transmitter above sea water and R is the earth's radius.

Transmission Range >

d LOS

d LOS = 2 2hR + h ≈ 2 2Rh 2

Fig.3. The maximum distance at which they can see each other d LOS occurs when the sighting line just grazes the earth's surface.

R (earth's radius) = 6.38× 106 m

We developed an adjustable scheme to obtain this positional information of the neighboring nodes based on the distance of these nodes from the considered node, this distance starting from nodes within a single hop away (i.e. within direct transmission range) from the considered node, ranging to nodes two, three or more multiples of the transmission range away. Consider a snapshot of an ad hoc network consisting of 21 nodes shown in figure 4. Assume we want node (a) to get some guidance assisting it to avoid moving into Dead-Zones and giving it clearance to move into zones covered by the ad hoc network. To achieve this, we create a DZAC that explores the neighboring topology and issues guidance.

Fig.4. An ad hoc network consisting of 21 nodes.

Fig.5. Node (a) with the DZAC formulated with its 4 indicators.

Looking at figure 5 we will see that node (a) has a transmission range TR(a) that covers nodes {b, c, d, e, k, n, o}, so if node (a) sends a Positional Information Request (PI-REQ) packet to the ad hoc network with information that it only needs Positional Information Reply (PI-REP) packets from nodes within direct transmission range from it. It will receive separate (PI-REP) packets from {b, c, d, e, k, n, o} containing X, Y coordinates of each one of these nodes.

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The node (a) then processes these (PI-REP) packets and attempts to create the DZAC by obtaining each (PI-REP) packet and extracting the X, Y coordinates in it and checking to which sector {S(1), S(2), S(3), S(4)} with-in the transmission range circle it belongs. The transmission range circle is the circle with the center being the X, Y coordinates of node (a) and the radius being the transmission range TR (a). The result will be the formation of the DZAC which has 4 indicators showing the number of nodes in each sector of the transmission range circle of node (a) thus orienting node (a) about areas in which it can safely move into, these areas being the sectors with a high number of nodes and areas it should avoid which are areas with low or no nodes present. Looking in figure 5 once more, we see node (a) can safely move into sectors {S(1), S(3), S(4)} but should avoid moving in sector 2.

2.1 Extending the DZAC exploration scope In order to ensure that the DZAC gives trustable indications, we enabled the DZAC to be formulated according to (PI-REP) packets retrieved from nodes within 2 or more transmission ranges instead of receiving (PI-REP) packets from nodes within direct transmission range of the node formulating the DZAC. Let's assume that the DZAC is to be formulated according to (PI-REP) packets retrieved from nodes within 2 transmission ranges (2 x TR (a)) from node (a) as shown in figure 6. Node (a) sends (PIREQ) packets to nodes within its' direct transmission range. These nodes not only reply with (PI-REP) packets but also forward the (PI-REQ) packets to all nodes within their transmission range. In turn, those nodes first check if they are within (2 x TR (a)) distance from node (a) or not. If they are within (2 x TR (a)) distance from node (a), they send a reply with a (PI-REP) packet, and continue forwarding the (PI-REQ) packets to all nodes within their transmission range, else they ignore the (PI-REQ) packets and avoid forwarding any more (PI-REQ) packets.

Fig.6. Node(a) with its DZAC formulated according to (PI-REP) packets retrieved from nodes within 2 transmission ranges from node (a)

Fig.7.

DZAC indicators increased to 8 readings.

2.2 Increased resolution of DZAC indicators Another modification that can be added to the Dead-Zone Avoidance Algorithm to increase the DZAC indicators to 8 instead of just 4 to give each node even more precise indications on which areas to avoid moving to. From looking at figure 7 we can notice that node (a) should avoid moving in Sectors {S(3), S(4) ,S(5)} as they have very low values.

2.3 Testing the DZAC indicators Before performing a thorough performance evaluation on the Dead-Zone Avoidance algorithm, in this section we briefly prove that the DZAC indicators will provide significant help to nodes and prevent them from entering areas where ad hoc network nodes don't cover. Figure 7 shows that the DZAC indicators will warn node (a) from moving in the sectors {S(3), S(4) ,S(5)} as they have a very low value. This information coincides with figure 8 which shows that S{4} contains the most hatched areas that represent Dead-Zones and sectors {S(3), S(5)} both contain only a single node thus have a high risk of becoming a Dead-Zone if this single node moves out of the sector or disconnects from the ad hoc network entirely.

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Fig.8.

Showing Dead-Zones in a specific rectangular area from the Ad hoc network topology

2.4 Indicators as percentages Furthermore, in order to facilitate decisions taken by nodes to avoid moving into specific sectors based on the DZAC indictor readings, DZAC indicators should be presented as relative percentages instead of mere values.

Indicator (i )% = Indicator Indicator(1) Indicator(2) Indicator(3) Indicator(4) Indicator(5) Indicator(6) Indicator(7) Indicator(8)

(100 xIndicator (i )) Indicatormax

Value 3 5 1 0 1 2 2 2

Percentage 60% 100% 20% 0% 20% 40% 40% 40%

Table I Showing Indicators 3, 4 & 5 having the least percentages thus highest risk of entering a Dead-Zone

2.5 Integrating with Location Based Routing Protocols Location based routing protocols use positional information to reduce the search space for a desired route. Limiting the search space results in fewer route discovery messages. The Dead-Zone Avoidance Algorithm can be used with any available Location Based routing protocols like LAR [4, 9], DREAM [5], LOAR [6] and LAKER [7] as they all provide the positional information needed for the algorithm to function properly. In this paper, we implemented our Dead-Zone Avoidance Algorithm with the LAR protocol. A couple of design considerations have been taken into account when we designed the DeadZone Avoidance Algorithm; these considerations tackle the issue of avoiding high control packets overhead.

2.5.1 DZAC Exploration scope As discussed earlier, by extending the DZAC exploration scope, we can obtain more reliable DZAC indicator readings. But this isn't achieved without cost, as by extending the DZAC exploration scope, higher cost is incurred in terms of control packets (PI-REQ & PI-REP packets). So there exists a tradeoff here.

2.5.2 DZAC formulation timings Another design consideration is the timings at which we attempt to formulate the DZAC. One option will be to choose a fixed time interval at which the DZAC will attempt to refresh its values according to the updates in the positional information of the nodes lying within the exploration scope of the node requesting the DZAC. The time interval should be chosen according to the degree of mobility of the nodes in the ad hoc network, with short time intervals given to nodes with high degree of mobility and longer time intervals to nodes with lower degree of mobility. Once again there is a tradeoff here, the smaller the time interval, the more reliable the DZAC indicators, the higher the cost, and vice versa.

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Another option will be to formulate the DZAC upon receiving a manual request done by the node requesting the DZAC. This can lead to a dramatic decrease in the control packets overhead but that will raise the risk that the node will enter a Dead-Zone without getting any prior warnings from the DZAC indicators.

3 Performance Evaluation In order to evaluate our Dead-Zone Avoidance Algorithm, we performed 3 scenario based simulations with the DSR protocol [8], the LAR protocol and the LAR protocol with Dead-Zone avoidance Algorithm integrated with it. We performed our simulations on a discrete event simulator called LBRP Simulator (Location-Based Routing Protocol Simulator) which we developed in our labs in Ain Shams University.

Fig.9 A snapshot of the Network Animator in LBRP Simulator.

3.1 Simulation Environment Regarding the simulation environment, we decided that an ad hoc network of 50 nodes will be installed on a simulation area of 1000,000 squared meters (1000 x 1000m). Initial positions (X and Y coordinates) of the nodes are obtained by using a uniform distribution. Each node makes 900 “moves” during the simulation. During a given move, a node travels a distance d, where d is uniformly distributed with a maximum of 15m. Various wireless transmission ranges are used in different simulation runs, ranging from 200 to 600 meters, with the assumption that all nodes have the same transmission range in each separate simulation run. Data traffic was generated using constant bit rate (CBR) UDP traffic sources, with 20 mobile nodes acting as traffic sources each generating 4 packets/s. Each simulation runs for 900 seconds of simulation time. The mobility model we chose to use is the "Random Waypoint". In this mobility model, each mobile node moves independently during the simulation. The parameter pausetime reflects the degree of mobility. When pausetime is 0 seconds, it means that all nodes are moving all the time and the ad hoc network has a high degree of mobility. When pausetime is 900 seconds, it means that all nodes are stationary during the simulation. We use a pausetime of 0 seconds in all simulations reflecting the continuous motion of the mobile nodes. The complete set of Simulation parameters are listed in Table II Simulation Parameter Value Simulation time 900s (15 min) Simulation area 1000x1000 m Number of Mobile Nodes 50 200,300,400,500 and 600 m Transmission range Movement model random waypoint Maximum speed 15 m/s Pause time 0s CBR sources 20 Packet rate 4 packets/s Table II Simulation parameters Regarding the Dead-Zone Avoidance Algorithm, we decided to use an exploration scope of one transmission range to avoid excessive routing overhead. The fixed time interval at which each node will attempt to formulate the DZAC was chosen to be 3 seconds. Typically, using a time interval longer than this will decrease the routing overhead yet produce less accurate DZAC indicators.

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3.2 Simulation Results In our simulation results we considered the following evaluation metrics: data packet delivery ratio and protocol overhead. The data packet delivery ratio is the ratio of the number of data packets delivered to the destination nodes divided by the number of data packets transmitted by the source nodes. Figure 10 gives an indication of how the LAR protocol aided with the Dead-Zone Avoidance Algorithm (DZA-LAR) performs. Data packet delivery ratio of (DZA-LAR) is generally higher when compared to DSR and LAR protocols regardless of the transmission range. DZA-LAR performed its best when transmission range was 600m and data packet delivery ratio increased by 0.51% when compare to data packet delivery ratio of LAR, while at the transmission range of 300m, the DZA-LAR data packet delivery ratio increased by 0.20% over its LAR counterpart.

Fig.10 The Effect of various transmission ranges on data packet delivery ratio

Figure 11 shows the effect of various transmission ranges on the routing overhead. Typically, the routing overhead decreases with the increase in the transmission range as a larger transmission range is accompanied with a smaller frequency of route discoveries. But due to the control packets (PI-REQ & PIREP) that are sent periodically in the DZA-LAR to formulate the DZAC, the overhead accompanying DZA-LAR is generally higher than that of the DSR and LAR.

Fig.11 Routing Protocol overhead Versus Transmission Range

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4 Conclusion In this paper we described the Dead-Zone Avoidance Algorithm which provides means to assist mobile nodes avoid moving into zones where the ad hoc network nodes can not reach (Dead-Zones). The algorithm functions by exploiting the positional information provided in the form of X, Y coordinates obtained from neighboring nodes and uses this information to formulate a Dead-Zone Avoidance Compass (DZAC) which shows each node safe region that it can move into and still be part of the ad hoc network. Once the Dead-Zone Avoidance Compass is created, it is up to the mobile node to decide whether to use the information presented by the DZAC or not because the information presented by the DZAC is merely for guidance and not for enforcement, but if the node be it a rescue officer in an disaster emergency operation or a soldier in enemy territory neglects the information presented by the DZAC, it can lead to the removal of this node from the ad hoc network if it moves into a Dead-Zone and consequently the possibility of failing to reestablish connection once more with the ad hoc network. Finally, we proved that by using information provided by the DZAC, and preventing nodes from moving into Dead-Zones, the overall performance of the ad hoc network using DZA-LAR (Dead-Zone Avoidance Location-Aided Routing Protocol) as a routing protocol was improved when compared to similar ad hoc networks using DSR and LAR as a routing protocol. The ad hoc network using DZA-LAR gave higher data packet delivery ratio, but its control packet overhead was higher than networks using DSR and LAR as routing protocols. Further work is needed to attempt to decrease the overhead of the DZA-LAR; possibly by using cached positional information in the nodes instead of the control packets sent to discover the position of neighboring nodes.

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