Omer Chughtai

Reliability-constrained routing for traffic load balancing in Wireless Sensor Networks

In recent years, a notable progress has been observed in the field of Wireless Sensor Networks (WSNs) due to their enormous number of applications. In this paper, a routing problem has been considered in a static WSN. Traditionally, routing mechanisms are based on a single objective optimisation function, e.g., the cost in terms of distance to find the shortest End-to-End (ETE) path from a source (S) to a destination (D). This behaviour may not be appropriate for long term reliable communication. We have considered a reliability-constrained multi-objective optimisation problem that implicitly captures the traffic load based on the Packet Delivery Ratio (PDR) along with the hop-count. The proposed technique selects an optimum ETE reliable path. The reliability is achieved by selecting the nodes with least congestion along the path from S to D that eventually balance the traffic load in the network. The result shows that the PDR and the hop count have a significant impact to select the best reliable ETE path.

ZGLS: a novel flat quorum-based and reliable location management protocol for VANETs

In location management services, a destination advertises its position attributes to a set of vehicles called location servers while, a source obtains these attributes from such location servers to track destination. The location management techniques in VANET have been categorized into flooding-based, flat hashing-based, hierarchical hashing-based and hierarchical quorum-based techniques. In flooding-based location service, destination information is flooded to the entire network which results into high congestion, low throughput and non-scalable network. In flat hashing, a global hash function is applied to compute location servers of each destination which results into higher delay, drop and signaling overhead in large VANETs. In hierarchical hashing, global hash function computes location servers of destination in hierarchical order. It therefore suffers from handover signaling between servers, high load on the top hierarchy and location query delay when source and destination are apart. In hierarchical quorum-based, location servers are identified cluster-wise and therefore it also suffers from the problems similar to hierarchical techniques. To overcome these problems, ZoomOut Geographic Location Service (ZGLS) protocol is proposed which introduces flat quorum-based location management service. In contrast to the aforementioned techniques, the novelty of ZGLS lies in the fact that it has shifted the location server role from hashing-based or clustering-based geographic areas to few 1-hop neighbours, called relatives. The proposed protocol creates a chain of relatives to provide positioning and tracking service. To evaluate signalling overhead, timeliness and the reliability of update and query packets, ZGLS is compared with RLSMP and HRHLS through ns-2 simulations. The results reveal that ZGLS stands out as a better choice for large-scale sparse and dense VANETs.

A congestion-aware and energy efficient traffic Load balancing Scheme for routing in WSNs

Most of the on-demand routing protocols in WSNs are designed with the aim to find the best path based on a single routing metric such as minimum hop count, so that the End-to-End (ETE) delay can be minimized. In these protocols, the probability to select the same sensor node(s) all the time is high, resulting in overloaded nodes and increased energy consumption per node. Furthermore, in these protocols, each intermediate node acts only on the first request it receives and the subsequent requests are ignored during route discovery, leading to suboptimal routes. In this paper, the Congestion-aware energy efficient and traffic Load balancing Scheme (CLS) for routing in WSNs is proposed. This scheme utilizes the ignored information during the route discovery process and considers a composite metric that incorporates the consumed energy E, participation level P of the node and signal strength S of the link between the nodes. In addition, through extensive simulations using ns-2.35, we demonstrate the effect of weighted additive approach against the lexical approach for multi variable routing metric.

Distributed on-demand multi-optional routing protocol in multi-hop wireless networks

In Wireless Sensor Networks (WSNs), fair utilisation of the network resources is a challenging task. In this regard, one of the determining factors is the routing protocol that plays an important role to route the data traffic from the source to the destination, under limited network resources. Most of the routing protocols and their variants in WSNs replace the routing metric of the prevalent routing protocol with their proposed routing metric and keep the route discovery mechanism intact. However, replacing only the routing metric is insufficient to improve the performance of the entire network as it can generate high End-to-End (ETE) delay in finding the destination as per the routing criteria. In this paper, a novel single path loop-free Distributed On-demand Multi-Optional routing (DOMO) protocol is presented. The DOMO selects the best sensor node based on the routing metric(s) amonst various alternatives at each stage during forward route formation. A simulation has been performed in ns-2.35 and it has been observed that, using the same routing metric(s), DOMO performs better for long-term communication in WSNs as compared to Ad hoc On Demand Distance Vector (AODV). The results have revealed that DOMO improves the average ETE delay by 17% and normalises the routing load by 47% as compared to AODV.

ZoomOut HELLO: A Novel 1-Hop Broadcast Scheme to Improve Network QoS for VANET on Highways

On highways, each vehicle uses periodic 1-hop broadcast messages to advertise its position and other information so that vehicles in the vicinity and those which are hops away can find the advertising vehicle for information exchange. During destination discovery, a vehicle issues broadcast messages, which travel hop by hop in search of destination. We argue that since periodic 1-hop messages are sent on regular intervals, so these can be manipulated in such an intelligent way that routing protocols may not need to execute broadcast destination discovery procedure. The continuous periodic HELLO broadcast mechanism can assist the routing protocol in this regard. The proposed ZoomOut HELLO (ZOH) technique introduces a neighbour-cum-forwarding (NF) table. In this scheme, periodic ZOH mechanism will populate the NF table, while the forwarding mechanism will use it. We introduce the concepts of Front and Behind relatives, which are selected out of 1-hop neighbours based on the typed HELLO messages exchanged between 1-hop neighbours. ZOH is a broadcast suppression technique and implicitly provides chain of relatives in the front and behind direction of each vehicle. A routing protocol can therefore use this chain. We have developed analytical model for ad-hoc on-demand distance vector (AODV), preferred group broadcast (PGB), reliable opportunistic broadcast (R-OB-VAN) and ZoomOut HELLO, and implemented them in MATLAB. The results show that ZoomOut HELLO generates least number of RREQ rebroadcast messages and has minimum network delay due to RREQ messages.

ZLS: A next-door lightweight QoS aware location service technique for VANET on highways

In VANET, a Location service technique comprises of location update and location request. In location update, a destination vehicle advertises its services and location to a set of vehicles called location servers. In location request, a source vehicle queries location servers in its broadcast range about the location and services of destinations. During location update, separate control messages are exchanged to periodically update location servers which create delay and congestion in the network. Similarly, after location request, pre-loaded digital maps at source vehicle are used to find the shortest path towards destination which does not give vehicle density on road at that moment in time. Other than digital maps, Dijkstra or Bellmen ford algorithms at source or intermediate nodes are also used to find shortest path, which is a computationally time consuming activity leading to an extra delay during path finding and before packet transmission. We therefore propose QoS and traffic density aware location service technique called ZoomOut Location Service (ZLS). We have implemented ZLS in NS2.33. The simulation results for highway traffic show that ZLS updates its location servers in a uni-cast fashion such that the location servers have up-to-date information of advertised services and destination position. Similarly, a source can reach destination in the quickest possible way by sending uni-cast messages without using digital map or shortest path finding algorithms.

A node/link level congestion detection approach in low power and limited broadcast range wireless ad hoc networks

With the advancements in the development of low power and limited broadcast range wireless ad hoc networks that support high data rate applications, the probability of information loss due to congestion is very high. One important factor is the timely detection of congestion that significantly improves the performance of the network. Currently most of the solutions either try to periodically/continuously examine the residual buffer space of the node or monitor the link utilisation. These types of solutions either consume high energy and processing or increase the link utilisation for the control packets that leads to the performance degradation of the network. To address this problem, a novel node/link level congestion detection approach (NLCA) has been proposed to timely detect congestion with the minimal processing overhead. The node-level congestion is detected by using the traditional mechanism of examining the buffer utilisation. However, the link-level congestion is detected by using a novel procedure that examines the wireless link utilisation with the counter maintained in CSMA/CA back-off stage. The instantaneous throughput based on the simulation analysis performed in ns-2.35 shows that NLCA can be used to timely detect congestion in the network.

A novel congestion alleviation procedure in multi-hop wireless sensor networks

The congestion problem usually occurs due to multiple traffic flows in a mono-sink wireless sensor network (WSN) which leads to excessive energy consumption and severe information loss. To solve this problem, a novel Congestion Alleviation Procedure (CAP) has been proposed. It exploits the characteristics of the sensor nodes and the wireless links between them. CAP mitigates congestion reactively by either bypassing the affected node and wireless link or rerouting the traffic to a less congested and energy efficient route. The performance evaluation based on the simulation performed in the network simulator (ns-2.35) shows that CAP improves Packet Delivery Ratio (PDR) by 45%, throughput by 39%, ETE delay by 32%, and energy consumption per data packet by 47% as compared to No Congestion Control (NOCC) mechanism.

A novel route discovery procedure for congestion avoidance in multi-hop WSNs

Due to high data traffic and resource-constrained nature of the wireless sensor network (WSN), congestion occurs which leads to severe packet loss and high energy consumption. Since an efficient route discovery procedure can avoid congestion and balance the traffic load, a reliable congestion-aware routing is important and requires careful design consideration. In this paper, a novel route discovery procedure for congestion avoidance (RDCA) in multi-hop WSNs has been proposed. RDCA is based on an objective function that incorporates the implicit behaviour of traffic load and consumed energy of the sensor nodes and signal strength between them along with the hop count. The results show that RDCA has a significant impact over energy, traffic load, and link quality aware ad hoc routing (ETLAODV) and energy efficient and QoS based routing (EQSR) in terms of packet delivery ratio (PDR), end-to-end (ETE) delay, energy consumption, and throughput.

Distributed vertical handover management for wireless mesh networks

Operators and wireless internet service providers are increasingly using Wireless Mesh Networks (WMN) to offer Internet connectivity, as it allows fast, easy and affordable network deployment and provide Internet services to the end user through all existing network technologies like Ethernet, WLAN, WiMAX, GPRS etc. Due to evolution of 4G heterogeneous wireless networks, todays mobile devices are equipped with multiple network interfaces. However, when an end user having these mobile devices moves across heterogeneous networks, the previously established communication may no longer remains active. We proposed the vertical handover management mechanism for a distributed IP based mobility management protocol (DIMMP) in WMN to provide seamless mobility with service continuation for mobile devices. Simulations were performed using NS2. Results show that handover delay is reduced significantly by DIMMP in comparison to MibileIP.