Jari Nieminen

Time Synchronization of Cognitive Radio Networks

In this paper, a novel synchronization protocol is proposed especially for Cognitive Radio (CR) networks called CR-Sync. In a CR network, time synchronization is indispensable because of the requirements for coordinated and simultaneous quiet periods for spectrum sensing, as well as the common understanding of time frame/slot in many CR MAC designs. The proposed CR-Sync achieves network-wide time synchronization in a fully distributed manner, i.e., each node performs synchronization individually using CR-Sync. Contrary to many existing synchronization protocols that do not exploit CR attributes, the proposed protocol takes advantage of the potential multiple spectrum holes that are discovered by CR and distributes the synchronization of different pairs of nodes to distinct channels and thus reduces the synchronization time significantly. Detailed analysis of synchronization error and convergence time are provided. Results show that the proposed CR-Sync out-performs other protocols such as TPSN in CR networks.

Exploitation of multi-channel communications in industrial wireless sensor applications: Avoiding interference and enabling coexistence

Most of the current wireless sensor networks operate on crowded unlicensed frequency bands. Especially in industrial wireless sensor applications this causes problems because of the received interference from other systems and coexistence problems with other wireless sensor networks. Multi-channel communications can be utilized to improve the performance under interference and enable coexistence of different applications. In this paper we propose a novel multi-channel Media Access Control (MAC) approach designed especially for industrial wireless sensor networks, named Generic Multi-channel MAC protocol (G-McMAC). G-McMAC performs well in terms of delay and throughput while it is also robust to interference and enables coexistence. In addition, G-McMAC is flexible, scalable and easily implementable to various applications since it does not use predetermined frame structures. Our theoretical results imply that G-McMAC outperforms other existing solutions. In addition, simulation results from a real-world industrial scenario show that G-McMAC is applicable for industrial wireless sensor applications.

Network-Wide Time Synchronization in Multi-Channel Wireless Sensor Networks

Recent advances in wireless sensor technology have enabled simultaneous exploitation of multiple channels in wireless sensor systems. In this paper, a novel time synchronization algorithm is proposed for multichannel Wireless Sensor Networks (WSNs) called Multi-Channel Time Synchronization (MCTS) protocol. Time synchronization is critical for many WSN applications and enables efficient communications between sensor nodes along with intelligent spectrum access. Contrary to many existing protocols that do not exploit multi-channel communications, the protocol takes advantage of potential multiple channels and distributes the synchronization of different nodes to distinct channels and thus, reduces the convergence time of synchronization processes significantly.

Delay-Throughput Analysis of Multi-Channel MAC Protocols in Ad Hoc Networks

Since delay and throughput are important Quality of Service parameters in many wireless applications, we study the performance of different multi-channel Media Access Control (MAC) protocols in ad hoc networks by considering these measures in this paper. For this, we derive average access delays and throughputs in closed-form for different multi-channel MAC approaches in case of Poisson arrivals. Correctness of theoretical results is verified by simulations. Performance of the protocols is analyzed with respect to various critical operation parameters such as number of available channels, packet size and arrival rate. Presented results can be used to evaluate the performance of multi-channel MAC approaches in various scenarios and to study the impact of multi-channel communications on different wireless applications. More importantly, the derived theoretical results can be exploited in network design to ensure system stability.

Multichannel Communications in Wireless Automation: Interdependencies between Communication and Control Parameters

Exploitation of wireless communications in various automation applications brings indisputable benefits, which has proliferated research efforts in the field during the recent years. However, underlying wireless communication systems introduce problems to the wireless control systems, such as variable delays, information loss, and limited throughput. By using multiple frequency bands simultaneously, the performance of a wireless network can be enhanced. Since many control applications have strict requirements on delay and delay variations, it is important to understand the impact of communication systems on the performance of wireless automation systems with respect to delay. Hence, in this paper, we study how different communication parameters, such as packet arrival rate, number of channels, and packet size, affect the performance of control systems. We also derive bound on control system performance given the network properties. Our results show the tradeoff between the performance of the wireless multichannel communication system and the automation system. These results can, for example, be further exploited in system design to find out the maximum packet arrival rate with given control parameters.

Impact of heterogeneous packet sizes on flow fairness

We analyze the fairness of bandwidth sharing between competing flows when the flows use different packet sizes. For systems where router buffers are defined in packets, we notice that larger packets get preferential treatment. Specifically, in networks, where a higher capacity link is followed by a lower capacity link, packet loss seen by streams with bigger packet size is smaller. We verify our findings by simulating both UDP and TCP traffic in ns2.

Performance of target tracking applications in multi-channel wireless sensor networks

Several future wireless communication systems will exploit multiple frequency channels simultaneously to reduce delay, enhance throughput and/or improve robustness. Nevertheless, the impact of multi-channel communications on different applications has not been comprehensively studied even though it is of significant importance to understand the interdependencies between the communication and application parameters. In this paper we study the performance of networked estimation in contention-based multi-channel wireless sensor networks by focusing especially on the delay introduced by the Media Access Control (MAC) layer. We derive the required theoretical results and analyze the relationship between communication and estimation parameters in a target tracking application. In addition, we show how to optimize estimation performance by choosing appropriate estimation parameters with certain communication parameters and vice versa.

Advanced Communication Solutions for Reliable Wireless Sensor Systems

State-of-the-art Wireless Sensor Network (WSN) technology enables design and implementation of novel, intriguing applications that can be used to address numerous industrial, environmental, societal and economical challenges and thus, the importance and potential of WSNs are constantly growing. Wireless sensor nodes constituting a WSN consist of a sensor interface, microcontroller, memory and battery units together with a radio module. Hence, wireless sensor nodes are able to carry out distributed sensing and data processing, and to share the collected data using radio communications. In the beginning the development of wireless sensors was driven by military applications but the introduction of civilian wireless sensor systems has greatly diversified application domain which has further boosted research efforts in the field of wireless sensor networks. Present state of the evolution of wireless sensor nodes allows utilization of smart sensors to enhance the performance and robustness of WSNs.