http://www.csun.edu/~andrzej/COMP529-S05/papers/Mesh%20Networks%20Survey.pdf

Wireless mesh networks: a survey

Although many energy efficient/conserving routing protocols have been proposed for wireless sensor networks, the concentration of data traffic towards a small number of base stations remains a major threat to the network lifetime. The main reason is that the sensor nodes located near a base station have to relay data for a large part of the network and thus deplete their batteries very quickly. The solution we propose in this paper suggests that the base station be mobile; in this way, the nodes located close to it change over time. Data collection protocols can then be optimized by taking both base station mobility and multi-hop routing into account. We first study the former, and conclude that the best mobility strategy consists in following the periphery of the network (we assume that the sensors are deployed within a circle). We then consider jointly mobility and routing algorithms in this case, and show that a better routing strategy uses a combination of round routes and short paths. We provide a detailed analytical model for each of our statements, and corroborate it with simulation results. We show that the obtained improvement in terms of network lifetime is in the order of 500%.

/pdf/joint-mobility-and-routing-for-lifetime-elongation-in-10syy09rwy.pdf

Joint mobility and routing for lifetime elongation in wireless sensor networks

We propose a new link metric called normalized advance (NADV) for geographic routing in multihop wireless networks. NADV selects neighbors with the optimal trade-off between proximity and link cost. Coupled with the local next hop decision in geographic routing, NADV enables an adaptive and efficient cost-aware routing strategy. Depending on the objective or message priority, applications can use the NADV framework to minimize various types of link cost.We present efficient methods for link cost estimation and perform detailed simulations in diverse scenarios. Our results show that NADV outperforms current schemes in many aspects: for example, in high noise environments with frequent packet losses, the use of NADV leads to 81% higher delivery ratio. When compared to centralized routing under certain settings, geographic routing using NADV finds paths whose cost is close to the optimum.

/pdf/efficient-geographic-routing-in-multihop-wireless-networks-1xulz9lzdy.pdf

Efficient geographic routing in multihop wireless networks

We consider the problem of neighbor discovery in static wireless ad hoc networks with directional antennas. We propose several probabilistic algorithms in which nodes perform random, independent transmissions to discover their one-hop neighbors. Our neighbor discovery algorithms are classified into two groups, viz. Direct-Discovery Algorithms in which nodes discover their neighbors only upon receiving a transmission from their neighbors and Gossip-based algorithms in which nodes gossip about their neighbors' location information to enable faster discovery. We first consider the operation of these algorithms in a slotted, synchronous system and mathematically derive their optimal parameter settings. We show how to extend these algorithms for an asynchronous system and describe their optimal design. Analysis and simulation of the algorithms show that nodes discover their neighbors much faster using gossip-based algorithms than using direct-discovery algorithms. Furthermore, the performance of gossip-based algorithms is insensitive to an increase in node density. The efficiency of a neighbor discovery algorithm also depends on the choice of antenna beamwidth. We discuss in detail how the choice of beamwidth impacts the performance of the discovery process and provide insights into how nodes can configure their beamwidths.

/pdf/on-neighbor-discovery-in-wireless-networks-with-directional-3l58da7rxd.pdf

On neighbor discovery in wireless networks with directional antennas

A large number of ractical sensing and actuating applications require immediate notification of rare but urgent events and also fast delivery of time sensitive actuation commands. In this a er,we consider the design of efficient wakeup scheduling schemes for energy constrained sensor nodes that adhere to the bidirectional end-to-end delay constraints posed by such applications. We evaluate several existing scheduling schemes and propose novel scheduling methods that outperform existing ones.We also resent a new family of wakeu methods,called multi-parent schemes, which take a cross-layer a roach where multiple routes for transfer of messages and wakeup schedules for various nodes are crafted in synergy to increase longevity while reducing message delivery latencies. We analyze the power-delay and lifetime-latency tradeoffs for several wakeup methods and show that our proposed techniques significantly improve the performance and allow for much longer network lifetime while satisfying the latency constraints.

Wakeup scheduling in wireless sensor networks

Multi-path routing has been studied thoroughly in the context of wired networks. Ii has been shown that using multiple paths to route messages between any source-destination pair of nodes (instead of using a single path) balances the load more evenly throughout the network. The common belief is that the same is true for ad hoc networks, i.e., multi-path routing balances the load significantly better than single-path routing. We show that this is not necessarily the case. We introduce a new model for evaluating the load balance under multi-path routing, when the paths chosen are the first K shortest paths (for a pre-specified K). Using this model, we show that unless we use a very large number of paths (which is very costly and therefore infeasible) the load distribution is almost the same as single shortest path routing. This is in contrary to the previous existing results which assume that multi-path routing distributes the load uniformly.

/pdf/load-balancing-in-ad-hoc-networks-single-path-routing-vs-k1fp0natu6.pdf

Load balancing in ad hoc networks: single-path routing vs. multi-path routing

For energy-constrained stationary wireless networks of sensors, selection of links with high quality rate helps to ensure reliable long-term operation. During the implementation of a protocol targeting industrial applications of such systems, it was found that it is advantageous to acquire accurate information about the availability and quality of the RF communication links prior to the network topology formation. "Link assessment" as part of the initialization process, accomplishes this task by assessing a sufficient number of packets exchanged between neighboring nodes. This paper introduces and analyzes two different approaches to link assessment: The first approach is a random nondeterministic scheme that allows for a probabilistic guarantee of collision-free packet exchange. An alternative method is described which employs 'constant-weight codes' and provides a deterministic guarantee of success. In particular, a special class of constant-weight codes, known as optical orthogonal codes, are considered. Since, these codes are cyclically permutable, they make the link assessment process simpler, and therefore they are preferred over other codes. We evaluate the performance of these methods based on their energy consumption, time duration, and implementation complexity

/pdf/energy-efficient-link-assessment-in-wireless-sensor-networks-4vp9stvoeu.pdf

Energy-efficient link assessment in wireless sensor networks

Input Queued (IQ) switches have been very well studied in the recent past. The main problem in the IQ switches concerns scheduling. The main focus of the research has been the fixed length packet-known as cells-case. The scheduling decision becomes relatively easier for cells compared to the variable length packet case as scheduling needs to be done at a regular interval of fixed cell time. In real traffic dividing the variable packets into cells at the input side of the switch and then reassembling these cells into packets on the output side achieve it. The disadvantages of this cell-based approach are the following: (a) bandwidth is lost as division of a packet may generate incomplete cells, and (b) additional overhead of segmentation and reassembling cells into packets. This motivates the packet scheduling: scheduling is done in units of arriving packet sizes and in nonpreemptive fashion. In M.A. Marsan et al. (2001) the problem of packet scheduling was first considered. They show that under any admissible Bernoulli i.i.d. arrival traffic a simple modification of maximum weight matching (MWM) algorithm is stable, similar to cell-based MWM. In this paper, we study the stability properties of packet based scheduling algorithm for general admissible arrival traffic pattern. We first show that the result of Marsan et al. extends to general regenerative traffic model instead of just admissible traffic, that is, packet based MWM is stable. Next we show that there exists an admissible traffic pattern under which any work-conserving (that is maximal type) scheduling algorithm will be unstable. This suggests that the packet based MWM will be unstable too. To overcome this difficulty we propose a new class of "waiting" algorithms. We show that "waiting"-MWM algorithm is stable for any admissible traffic using fluid limit technique.

/pdf/input-queued-switches-cell-switching-vs-packet-switching-238uckckqd.pdf

A. Keshavarzian

Papers

Load balancing in ad hoc networks: single-path routing vs. multi-path routing

Energy-efficient link assessment in wireless sensor networks

Input queued switches: cell switching vs. packet switching