Monday, February 7, 2011
Ad Hoc Positioning System (APS)
In this paper authors proposed a distributed, hop by hop positioning algorithm (APS) to provide approximate location for all nodes in a network. The key features of APS are that it is decentralized, it does not need special infrastructure and provides absolute positioning. They used simplified version of the GPS triangulation. In this for an arbitrary node to estimate its own position in the plane it has to have estimates to a number (atleast 3) of landmarks. Immediate neighbors of the landmark use signal strength measurement to estimate the distance to landmark where as second hop neighbors can use any of the three propagation methods discussed in this paper. The authors proposed and discussed about the pros and cons of DV-Hop propagation method, DV-distance propagation method and Euclidean propagation method. They did simulations to evaluate the performance of the proposed propagation methods. They conclude stating that actual locations obtained by APS are on average less than one radio hop from the true location and positions produced by APS are usable by geodesic and geographic routing algorithms.
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ReplyDeleteThe main aim of the paper trying to get routing with out routing tables.The APS works as an extension of both distance vector routing and GPS positioning.In APS the node finds it's estimated location with the help of 3 landmarks and then finds the exact location with the help of GPS.This paper says that Euclidian and Dv-distance models are very accurate and gives minimum location error. The geographical routing works well if localization is good. But the paper does not give the information about trade off between density of network,node capabilities,quality of node position obtained(Accuracy),and ratio of landmarks.
ReplyDeleteWe saw that this paper mostly took into account whether or not it's location results were sufficient enough for the purpose of Geographical Routing. But I don't believe that the location results this protocol gives would be precise enough for other purposes. Coverage wouldn't be able to be based off these numbers without having a serious flaw in how accurate the coverage is.
ReplyDeleteThe technology introduced in this paper i.e.APS seems very reliable and efficient as compared to GPS in almost every manner.But once pratically implemented it can definitely revolutanize the sensor technology. This paper proposed various algorithms like DV hop and Euclidean,given the algorithms have their own set of advantages and disadvantages.But the only thing I didn't understand is which of these algorithns is still more relaible than the other. In conclusion, given the techonolgy introduced might have some flaws asssociated with it, but still this paper explains the proposed new technology very efficiently.
ReplyDeleteThe fact that the algorithm is decentralized makes it light weight. However the algorithm assumes the presence of at least 3 landmarks, whose location is know. The position estimate obtained based on landmark positions though may be less erratic for nodes closed to the landmarks, the error gets magnified as we move to nodes away from the landmarks. In this regard, I agree with Alex that the algorithm may only prove suitable for geographical routing where only relative position matters for routing decisions.
ReplyDeleteSo if I understand correctly, the landmarks are nodes with GPS. The rest of the nodes use the DV hop and Euclidian algorithms to calculate its position by using the landmarks as reference. In my thinking, this is a bit weird, it is like having a system using rechargable batteries but that depends on some non-rechargeable ones. Anyway, just my thinking. Still, it is great that only a few landmarks with GPS can be used for many other nodes to be localized, just by performing calculations with their corresponding algorithms.
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