Alireza Shahrabi

Comparative Study of Reactive and Proactive Routing Protocols Performance in Mobile Ad Hoc Networks

The mobility of nodes in mobile ad hoc networks (MANETs) results in frequent changes of network topology making routing in MANETs a challenging task. Some studies have been reported in the literature to evaluate the performance of the proposed routing algorithms. However, since the publication of experimental standards for some routing protocols by IETF, little activity has been done to contrast the performance of reactive against proactive protocols. This paper evaluates the performance of reactive (AODV, DSR) and proactive (OLSR) routing protocols in MANETs under CBR traffic with different network conditions. Our results, contrarily to previously reported studies conducted on the same routing protocols, show the superiority of proactive over reactive protocols in routing such traffic at the cost of a higher routing load.

An Analytical Performance Model for the Spidergon NoC

Networks on chip (NoC) emerged as a promising alternative to bus-based interconnect networks to handle the increasing communication requirements of the large systems on chip. Employing an appropriate topology for a NoC is of high importance mainly because it typically trade-offs between cross-cutting concerns such as performance and cost. The spidergon topology is a novel architecture which is proposed recently for NoC domain. The objective of the spidergon NoC has been addressing the need for a fixed and optimized topology to realize cost effective multi-processor SoC (MPSoC) development [7]. In this paper we analyze the traffic behavior in the spidergon scheme and present an analytical evaluation of the average message latency in the architecture. We prove the validity of the analysis by comparing the model against the results produced by a discrete- event simulator.

A Novel Cooperative Opportunistic Routing Scheme for Underwater Sensor Networks.

Increasing attention has recently been devoted to underwater sensor networks (UWSNs) because of their capabilities in the ocean monitoring and resource discovery. UWSNs are faced with different challenges, the most notable of which is perhaps how to efficiently deliver packets taking into account all of the constraints of the available acoustic communication channel. The opportunistic routing provides a reliable solution with the aid of intermediate nodes’ collaboration to relay a packet toward the destination. In this paper, we propose a new routing protocol, called opportunistic void avoidance routing (OVAR), to address the void problem and also the energy-reliability trade-off in the forwarding set selection. OVAR takes advantage of distributed beaconing, constructs the adjacency graph at each hop and selects a forwarding set that holds the best trade-off between reliability and energy efficiency. The unique features of OVAR in selecting the candidate nodes in the vicinity of each other leads to the resolution of the hidden node problem. OVAR is also able to select the forwarding set in any direction from the sender, which increases its flexibility to bypass any kind of void area with the minimum deviation from the optimal path. The results of our extensive simulation study show that OVAR outperforms other protocols in terms of the packet delivery ratio, energy consumption, end-to-end delay, hop count and traversed distance.

Congestion adaptive multipath routing for load balancing in Mobile Ad hoc Networks

Congestion control and load balancing have been challenging tasks in Mobile Ad hoc Networks (MANET) due to the dynamic and un-predictable behaviour and topology change of such networks. For effective load balancing and congestion control, routing metrics need to accurately capture the load in various locations of the network. In this paper, we present a congestion adaptive multipath routing protocol to increase the throughput and avoid congestion in MANETs. In our approach when the average load of an existing link increases beyond a defined threshold and the available bandwidth and residual battery energy decreases below a defined threshold, traffic is distributed over fail-safe multiple routes to reduce the traffic load on a congested link. Through simulation results, we show that our proposed approach achieves better throughput and packet delivery ratio with reduced delay for constant bit rate (CBR) traffic when compared with QMRB, a protocol using mobile routing backbones.

DibA: An Adaptive Broadcasting Scheme in Mobile Ad Hoc Networks

Broadcasting is a vital communication mechanism in Mobile Ad Hoc Networks, as it is the key element for exchanging control packets to support some services such as management and routing protocols. Simple Flooding, which is mostly used as the broadcasting mechanism, is neither resource efficient nor reliable especially in high populated and dense networks. The Distance-Based(DB) scheme is one of the schemes proposed to alleviate the Flooding effects. However, DB uses constant pre-determined distance threshold value regardless of network dynamics. In this paper, we propose an adaptive Distance-Based (DibA)scheme, which locally determines the density of the network and adjusts the distance threshold of everyr ebroadcasting operation without relying on HELLO packets or GPS systems. Our simulation study shows that our proposed scheme achieves considerable performance improvement over DB while the average value of transmission packets is not a function of network size.

HETEROGENEOUS 3D NETWORK-ON-CHIP ARCHITECTURES: AREA AND POWER AWARE DESIGN TECHNIQUES

Three-dimensional Network-on-Chip (3D NoC) architectures have gained a lot of popularity to solve the on-chip communication delays of next generation System-on-Chip (SoC) systems. However, the vertical interconnects of 3D NoC are expensive and complex to manufacture. Also, 3D router architecture consumes more power and occupies more area per chip floorplan compared to a 2D router. Hence, more efficient architectures should be designed. In this paper, we propose area efficient and low power 3D heterogeneous NoC architectures, which combines both the power and performance benefits of 2D routers and 3D NoC-bus hybrid router architectures in 3D NoC architectures. Experimental results show a negligible penalty (less than 5%) in average packet latency of the proposed heterogeneous 3D NoC architectures compared to typical homogeneous 3D NoCs, while the heterogeneity provides power and area efficiency of up to 61% and 19.7%, respectively.

Void-Handling Techniques for Routing Protocols in Underwater Sensor Networks: Survey and Challenges

From the view of routing protocols in underwater sensor networks (UWSNs), the presence of communication void, where the packet cannot be forwarded further using the greedy mode, is perhaps the most challenging issue. In this paper, we review the state of the art of void-handling techniques proposed by underwater geographic greedy routing protocols. To this, we first review the void problem and its negative impact on the category of the geographic greedy routing protocols, which does not entail any void recovery technique. It is followed by a discussion about the constraints, challenges, and features associated with the design of void-handling techniques in UWSNs. Afterward, currently available void-handling techniques in UWSNs are classified and investigated. They can be classified into two main categories: 1) location-based and 2) depth-based techniques. The advantages and disadvantages of each technique along with the recent advances are then presented. Finally, we present a qualitative comparison of these techniques and also discuss some possible future directions.

Low power heterogeneous 3D Networks-on-Chip architectures

Three dimensional Network-on-Chip (3D NoC) architectures have evolved with a lot of interest to address the on-chip communication delays of modern SoC systems. In this paper we propose low power heterogeneous NoC architectures, which combines both the power and performance benefits of 2D routers and 3D NoC-bus hybrid router architectures in 3D mesh topologies. Experimental results show a negligible penalty of up to 5% in average packet latency of 3D mesh with homogeneous distribution of 3D NoC-bus hybrid routers. The heterogeneity however provides superiority of up to 67% and 19.7% in total crossbar area and power efficiency of the NoC resources, respectively compared to that of 3D mesh with homogeneous distribution of 3D NoC-bus hybrid routers.

An analytical performance model for the Spidergon NoC with virtual channels

The Spidergon Network-on-Chip (NoC) was proposed to address the demand for a fixed and optimized communication infrastructure for cost-effective multi-processor Systems-on-Chip (MPSoC) development. To deal with the increasing diversity in quality of service requirements of SoC applications, the performance of this architecture needs to be improved. Virtual channels have traditionally been employed to enhance the performance of the interconnect networks. In this paper, we present analytical models to evaluate the message latency and network throughput in the Spidergon NoC and investigate the effect of employing virtual channels. Results obtained through simulation experiments show that the model exhibits a good degree of accuracy in predicting average message latency under various working conditions. Moreover an FPGA implementation of the Spidergon has been developed to provide an accurate analysis of the cost of employing virtual channels in this architecture.

An analytical model of wormhole-routed hypercubes under broadcast traffic

A large number of algorithms have been proposed to support collective communication operations for scalable parallel systems over the past few years. When proposing a new algorithm for a collective communication operation, it is critical to determine its precise scope and evaluate it with accurate modelling of the underlying routing and communication mechanism. However, there has been comparatively little activity in the area of analytical models of these operations. As a result, most existing studies have relied on simulation to evaluate the performance merits of collective communication algorithms. This paper presents a new analytical model for predicting unicast and broadcast latency in the wormhole-routed hypercube. Results obtained through simulation experiments show that the model exhibits a good degree of accuracy in predicting message latency under different working conditions.