Sedat Atmaca

A Novel Cross-layer Routing Protocol for Increasing Packet Transfer Reliability in Mobile Sensor Networks

In mobile sensor networks (MSNs), sensor data is generally transferred via mobile sensor nodes by multi-hop fashion. Because of the mobility of the nodes in the network, the efficient routing protocols are needed to ensure end-to-end route reliability while incurring minimal power consumption and packet delay. In this study, we developed a new routing protocol to meet these requirements for MSNs based on a cross-layer interaction among five reference layers (application, transport, network, MAC and physical). The proposed protocol primarily exploits the idea of interaction among these five layers all-in-one protocol. Its primary goals are (i) to discover the most reliable route in network, (ii) to sustain the route reliability and (iii) to be energy efficient and delay aware. It has been designed, modeled and simulated by using OPNET Modeler simulation software. The simulation results of the proposed protocol have been compared to three well known routing protocols (i.e., AODV, Leach-Mobile, CBR-Mobile). According to the obtained results, the proposed protocol outperforms its counterparts in terms of route reliability and end-to-end delay performances.

Implementation of Skipjack cryptology algorithm for WSNs using FPGA

Networking and data communications security has become a vital requirement since the emergence and common use of computer networks. Concordantly, attempts which intent to break security precautions used in WSN applications have arisen as well. Paying attention to WSNs particular requirements, new security and cryptography methods are developed and employed in almost all WSN applications. The main goal of this presented work is to implement the Skipjack symmetric cryptography algorithm frequently employed in wireless networking security using FPGA hardware platform. A Digilent starter board with Xilinx FPGA has been utilized as hardware platform, and CodeGear C++ Builder 2009, Xilinx ISE Foundation and Visual Studio 2008 have been used as software platform.

A new QoS-aware TDMA/FDD MAC protocol with multi-beam directional antennas

With the ever-increasing demand for wireless real-time services and continuing emergence of new multimedia applications especially for mobile users, it is necessary for the network to support various levels of quality of service (QoS) while maximizing the utilization of scarce and expensive wireless channel resources. Considering this fact, a new TDMA/FDD MAC protocol integrating a novel QoS management algorithm and multi-beam Directional Antennas (DAs) to efficiently exploit wireless resources has been developed and presented in this paper. It supports all ATM CBR, VBR, ABR and UBR service classes by adopting a well-managed dynamic guarantee-based QoS scheduling algorithm. The work mainly aims at increasing the wireless system throughput as well as improving the call-blocking ratios and end-to-end delays for real-time applications. This seamless communication enables both handling real-time multimedia traffics in a fair manner and granting call requests on the basis of the connection types. The system has been developed, modeled and simulated using OPNET Modeler. The simulation results show that the QoS-aware TDMA/FDD MAC with multi-beam DAs has substantially increased the system throughput and that the call-blocking ratio has been reduced from 86% to 18%, when the proposed MAC with 8-Beam antennas is employed instead of the regular MAC.

Improving TDMA Channel Utilization in Random Access Cognitive Radio Networks by Exploiting Slotted CSMA

This paper aims to improve the spectrum efficiency of the licensed time division multiple access (TDMA) channel by exploiting the unused periods of primary users (PUs) in cognitive radio networks. A wireless network that consists of two classes of users, PUs and CR users, accessing a time slotted based common communication channel is considered. PUs employ TDMA and have always high priority over the CR users to access the channel. CR users utilize slotted Carrier Sense Multiple Access and can access the channel when it is not occupied by the PUs. New expressions for the throughput of both CR network and overall network have been derived in order to evaluate the channel utilization. Besides, an example network have been developed, modeled and simulated by using the OPNET Modeler simulation software with the purpose of verifying the analytical throughput results. The simulation results obtained under various network load conditions are consistent with the analytical results. This study has also proposed that the overall channel utilization can be improved by well exploiting the spectrum holes without interfering with the PU transmissions.

A modified sectoral sweeper-based localization estimation and its implementation in a multi-hop wireless sensor networking environment by using OPNET

In wireless sensor networks, location awareness along with the sensed data is important for most of the applications. Although there are many localization techniques in the literature, some of these techniques involve tiny sensor nodes, which need to be computationally powerful and complex in hardware to estimate their locations. This paper proposes a modified sectoral sweeper-based localization estimation (M-SSLE) method, which is the improved version of our previously studied SSLE method, to achieve position information of sensor nodes. This technique requires only a central node having a smart antenna capability to estimate locations of sensor nodes and simplified message formats. Using the SSLE technique, the computational burden for location estimation is carried out by a central node and no hardware or software modification to tiny sensor devices is required. The M-SSLE is implemented using an OPNET modeler for realistic fading channel conditions. The detailed implementation methodology in OPNET is presented in terms of node and process models. The performance of the M-SSLE method is evaluated through different network scenarios and channel parameters in terms of localization error, average throughput, and node energy consumption. Furthermore, its localization performance is compared with the SSLE and Cramér Rao Bound methods in the two different scenarios for the deployment of the sensor nodes. The M-SSLE average localization errors of 4.3 and 8.9 m are demonstrated under the log-distance and the log-normal shadowing channel conditions in a 250 m × 250 m area, respectively.

A new MAC protocol for broadband wireless communications and its performance evaluation

This paper presents a new Time Division Multiple Access/Frequency Division Duplexing (TDMA/FDD) based Medium Access Control (MAC) protocol for broadband wireless networks, supporting Quality of Service (QoS) for real-time multimedia applications. It also gives the Call Blocking Probability (CBP), packet end-to-end delay and utilization analysis of different service classes, as they are most essential performance criterions in broadband wireless network assessment. The Connection Admission Control (CAC) mechanism in the proposed MAC efficiently organizes the bandwidth allocation for different service classes by means of a fairness based scheduling algorithm. In addition, the simulation model of the proposed MAC scheme is realized by using OPNET Modeler network simulator. The results of the analytical calculations for the CBPs are compared to those of the simulation of the proposed MAC, thus validity of the MAC protocol is proved.

An integrated approach for analytical modeling of WSNs

Nowadays, with the ever-increasing use of the wireless sensor networks (WSNs) in parallel with developments in sensor and wireless communication technologies, modeling of these networks has also become essential. The analytical modeling is one of the basic approaches used for testing WSNs and verification of their abilities. The goal of this study is to build an analytical model for the performance metrics that allow making an integrated evaluation of a WSN application. The effects of the application layer components with the routing, MAC and security protocols on the performance metrics are obtained by using an analytical model based on an example WSN application scenario. The results obtained from the analytical models by using technical specifications of a common WSN node (MICAz) are presented and discussed.

Energy efficient hybrid MAC protocol for large scale wireless sensor networks

In this study, a hybrid, energy efficient MAC (Medium Access Control) protocol has been developed for usage in dense WSN (Wireless Sensor Network) applications. In the designed hybrid MAC, favorable aspects of both CSMA (Carrier Sense Multiple Access) and TDMA (Time Division Multiple Access) techniques are considered. Consequently, a MAC protocol which is more energy efficient than both CSMA and TDMA-based MAC protocols is aimed. Therefore, with the combination of CSMA which responses to the events rapidly and TDMA which reduces the collisions and unnecessary channel listening, high system throughput and node energy efficiency are obtained.

Throughput Maximization of CSMA in Cognitive Radio Networks with Cooperative Spectrum Sensing

This study aims the throughput maximization of carrier sense multiple access (CSMA) in random access cognitive radio networks (CRNs) by using cooperative spectrum sensing. In the cooperative spectrum sensing, multiple cognitive radio (CR) users individually monitor the spectrum for the primary users (PUs)’ activities and send their local decisions to the CR access point. Upon receiving the individual decisions, the CR access point gives the final decision about the PU’s presence at the spectrum and sends it to all CR users in the network. At decision stage, CR access point utilizes the k-out-of-N decision fusion rule with optimal k value in order to obtain maximum CRN throughput. In this paper, we model a CRN utilizing CSMA medium access control scheme and focus on analyzing the throughput performance of it. Throughput performances of our CRN model which separately utilizes AND, OR, MAJORITY fusion rules and k-out-of-N decision fusion rule with the optimum k value are obtained and compared under the same network level probability of detection constraint. The throughput results obtained show that our CRN model utilizing k-out-of-N decision fusion rule with the optimum k value achieves higher throughput performance than AND, OR and MAJORITY fusion rules when they all have the same CRN load.

A cluster based routing approach in LTE ad-hoc networks

In this work, a new routing algorithm which allows smart terminals to join the ad-hoc network at random times in order to carry out data transmission using Long Term Evolution (LTE) infra-structure has been developed and simulated by using OPNET Modeler. The routing scheme has been realized by clustering the terminals according to some predefined physical layer parameters and by utilizing Carrier Sense Multiple Access (CSMA) and Time Division Multiple Access (TDMA) schemes. After determining the cluster members and cluster head, time slot allocation process is carried out per cluster head and data gathered from the cluster members are relayed to the main server. The results show that the proposed algorithm utilizes less control packets during the path discovery than the widely used Ad hoc On-Demand Distance Vector (AODV). Besides, it has less route discovery time than AODV for all network loads.