Wireless Sensor Networks COE 499 Energy Aware Routing Tarek Sheltami KFUPM CCSE COE http://faculty.kfupm.edu.sa/coe/tarek/coe499.htm 4/23/2017

Outline Metric-based approaches Routing with diversity ETX metric MOR/MER Routing with diversity Relay diversity ExOR Multi-path routing Braided multi-path routing Gradient cost routing (GRAd) Gradient Broadcast routing (GRAB) Lifetime-maximization energy-aware routing techniques Power aware routing Lifetime maximizing routing Flow optimization formulations 4/23/2017

Metric-based approaches The ETX metric Minimizes the expected number of total transmissions on a path Let df be the packet reception rate on a link in the forward direction, and dr the probability that the corresponding ACK is received in the reverse direction Using Bernoulli trail, the expected number of transmission required successful delivery of a packet on the link is: The end-to-end paths are constructed to minimize the sum of ETX on each link on the path Minimizing the required number of transmissions improves bandwidth efficiency as well as energy efficiency One challenge in determining the values of df and dr , by performing an appropriate link monitoring procedure 4/23/2017

Metric-based approaches.. The ETX metric.. Only the forward probabilities are shown in the below figure Assume dr = 1 The direct link A-B incurs 10 retransmissions Link A-C-D-E-B incurs 1.11 retransmissions per link Link A-F-B incurs 1.25 retransmission per link, which is the ETX-minimizing path 4/23/2017

Metric-based approaches.. Metrics for energy–reliability tradeoffs (MOR/MER) ETX is not good for highly mobile environment Let d represent the distance between transmitter and receiver, η the path-loss exponent, SNR the normalized signal-to-noise ratio without fading, f the fading state of the channel, then the instantaneous capacity of the channel is described as: The outage probability Pout is defined as the probability that the instantaneous capacity of the channel falls below the transmission rate R: SNR∗=SNR/(2R−1) is a normalized SNR, and μ=E[|f|2] is the mean of the Rayleigh fading 4/23/2017

Metric-based approaches.. Theorems: The metric for each link is with a proportional power setting, which refer to minimum energy route metric and distance depedent MOR/MER metrics metric do not require the collection of link quality metrics (as in case of the ETX), but assume that the fading can be modeled by a Rayleigh distribution MOR/MER metrics does not take into account the use of acknowledgements 4/23/2017

Routing with diversity Relay diversity By allowing C to overhear A, it is shown that, in the high-SNR system, the end-to-end outage probability decays as (SNR)−2 When nodes within L hops can communicate with each other with high SNR, the end-to-end outage probability would decay as SNR−L Using this technique requires a larger number of receivers to be actively overhearing each message, which may incur a radio energy penalty 4/23/2017

Routing with diversity.. Extremely opportunistic routing (ExOR) Consists of three stages: selecting the forwarding candidates, acknowledging transmissions, and deciding whether to forward a received packet It is assumed that each node in the network has a matrix containing an approximation of the loss rate for direct radio transmission between every pair of nodes The first node in an ExOR forwarding sequence chooses a candidate subset of all its neighboring nodes which could bring the packet closer to the destination The sender lists this set in the packet header, prioritized by distance After transmission, each node that receives the packet looks for its address in the candidate list in the header Each recipient delays an amount of time determined by its position in the list before transmitting an acknowledgment 4/23/2017

Routing with diversity.. Extremely opportunistic routing (ExOR) Each node looks at the set of acknowledgments it receives to decide whether it should forward the packet The forwarding node rewrites the ExOR frame header with a new set of candidates and transmits the packet This process is repeated until the ultimate destination receives the packet 4/23/2017

Multi-path routing Braided multi-path routing A localization protocol is used to determine the locations of the nodes A braided path defined as one in which for each node on the main path there exists an alternate path from the source to the sink that does not contain that node, but which may otherwise overlap with the other nodes on the main path Gradient cost routing (GRAd) All nodes in the network maintain an estimated cost to each active destination The cost metric is the number of hops When a packet is transmitted, it includes a field that indicates the cost it has accrued and the TTL field for the packet Any receiver notes that its own cost is smaller than the remaining value of the packet can forward the message, as long as it is not a duplicate GRAd allows multiple nodes to forward the same message, which is a limited directed flood and provides significant robustness, at the cost of larger overhead 4/23/2017

Multi-path routing.. Gradient Broadcast routing (GRAB) Packets travel from a source to the sink, with a credit value that is decremented at each step depending on the hop cost An intermediate forwarding node with greater credit can consume a larger budget and send the packet to a larger set of forwarding eligible neighbors Each packet contains three fields Ro – the credit assigned at the originating node Co – the cost-to sink at the originating node U – the budget already consumed from the source to the current hop The first two fields never change in the packet, while the last is incremented at each step, depending on the cost of packet transmission To prevent routing loops, only receivers with lower costs can be candidates for forwarding. 4/23/2017

Multi-path routing.. Gradient Broadcast routing (GRAB).. 4/23/2017

Multi-path routing.. Gradient Broadcast routing (GRAB).. Each candidate receiver i with a cost-to-sink of Ci computes a metric called β and a threshold θ as follows: As long as β > θ the candidate node will forward the message 4/23/2017

Lifetime-maximization energy-aware routing techniques Power aware routing The basic power-aware routing scheme selects routes in such a way as to prefer nodes with longer remaining battery lifetime as intermediate nodes Ri is the remaining energy of intermediate node, ci,j is the metric cost function The goal is to minimize , where P is the path. 4/23/2017

Lifetime-maximization energy-aware routing techniques.. Lifetime maximizing routing Another metric is proposed, Ti,j, the transmission energy for each link i, j Let the initial energy of the transmitting node Ei: (a, b, c)=(0, 0, 0), we have a minimum hop metric; if (a, b, c)=(1, 0, 0), we have the minimum energy-per-packet metric; if b =c, then normalized residual energies are used, while c=0 implies that absolute residual energies are used; However, simulation results in the literature suggest that a non-zero a and relatively large b =c terms provide the best performance (e.g. (1, 50, 50)) 4/23/2017

Lifetime-maximization energy-aware routing techniques.. Flow optimization formulations Let there be n-numbered source nodes in the network, and a sink labelled n+1. Let fij be the data rate on the corresponding link, Cij the cost of transmitting a bit on the link, R the reception cost per bit at any node, T the total time of operation under consideration, Ei the available energy at each node, and Bi the total bandwidth available at each node. This linear program maximizes the total data gathered during the time duration T. It incorporates (a) a flow conservation constraint, (b) a per-node energy constraint, and (c) a shared bandwidth constraint. 4/23/2017