Showing papers by "Timo Hämäläinen published in 2010"

Robust Regulation of Distributed Parameter Systems with Infinite-Dimensional Exosystems

Abstract: In this paper a robust regulation problem for infinite-dimensional systems with infinite-dimensional exosystems is discussed. The input and output spaces are also allowed to be infinite-dimensional. A new definition of internal model in terms of the controller parameters is given. It is shown that there exists a feedback controller containing an internal model of the exosystem, which robustly regulates the class of signals generated by the exosystem and strongly or weakly stabilizes the closed-loop system. As far as the authors know, the results are new even for finite-dimensional systems with infinite-dimensional exosystems.

Energy-efficient reservation-based medium access control protocol for wireless sensor networks

Abstract: In Wireless Sensor Networks (WSNs), a robust and energy-efficient Medium Access Control (MAC) protocol is required for high energy efficiency in harsh operating conditions, where node and link failures are common This paper presents the design of a novel MAC protocol for low-power WSNs The developed MAC protocol minimizes the energy overhead of idle time and collisions by strict frame synchronization and slot reservation It combines a dynamic bandwidth adjustment mechanism, multicluster-tree network topology, and a network channel allowing rapid and low-energy neighbor discoveries The protocol achieves high scalability by employing frequency and time division between clusters Performance analysis shows that the MAC protocol outperforms current state-of-the-art protocols in energy efficiency, and the energy overhead compared to an ideal MAC protocol is only 285% to 271% The high energy efficiency is achieved in both leaf and router nodes The models and the feasibility of the protocol were verified by simulations and with a full-scale prototype implementation

Program image dissemination protocol for low-energy multihop wireless sensor networks

Abstract: A Wireless Sensor Network (WSN) consists of programmable, low-cost and resource-constrained nodes. Adding new features or error fixes requires reprogramming nodes. Manually reprogramming hundreds or thousands of nodes is impractical as it takes significant effort and time. Therefore, WSNs require a mechanism for updating the nodes program image, which contains the applications and protocols running on each node. Current protocols for updating program images rely on a large external memory that is used to temporary store program images. In this paper we present the design, implementation and experimental measurements of a lightweight and reliable Program Image Dissemination Protocol (PIDP) for autonomous adhoc multihop WSNs. PIDP requires no external memory storage, is independent of the WSN stack, offers a low overhead protocol for transferring program images, and can reprogram the whole WSN stack. An update procedure with PIDP in one part of the network does not interfere with the WSN elsewhere. PIDP was implemented on a node platform with an 8-bit 2 MIPS Microchip PIC18LF8722 microcontroller and a 2.4 GHz Nordic Semiconductors nRF24L01 radio. PIDP requires less than 7 kilobytes of program memory and from 22 to 815 bytes of data memory. In experiments PIDP reprogrammed a campus WSN, which is a running deployment of 178 nodes, in 5 hours.

Call and messaging performance comparison between IMS and SIP networks

Abstract: The IP Multimedia Subsystem (IMS) has been considered to be exclusive to big players of the telecommunication world. Session Initiation Protocol (SIP) has been standardized by IETF and solutions based on it have been in the market at least for a decade. It is also an essential part of the IMS, as it is the control protocol of IMS. Recent development of the Linux platform and the Open source IMS system has lead to a situation where the IMS is also an affordable solution for smaller telecommunication companies. The obvious question has been whether the level of performance with Open source IMS is really suitable for business usage. ETSI-TISPAN has unified IMS performance measurements by defining a common framework which to follow in measurements. The paper presents comparisons between IMS and SIP based networks in call and messaging performance. the Open IMS solution by the Fraunhover Focus Institute is compared with the OpenSIPS, an open source SIP server. The number of users in our measurements was chosen to be 100 000, a large enough number to be considered as a suitable number of users for small or moderate business usage needs. Our study shows that both of the systems are able to handle this many users and, in the case of OpenSIPS, with a clear margin. It was also discovered that both systems are reliable and are suitable for small and moderate business usage.

Decreasing the MAP overhead in the IEEE 802.16 OFDMA system

Abstract: One of the key performance bottlenecks of existent 802.16 systems is the downlink signalling overhead. It is caused by the MAP messages that carry information on the data burst allocations. To decrease the MAP overhead, the 802.16 standard proposes a few mechanisms, such as the compressed MAP and sub-MAPs. However, similarly to the scheduling discipline, an exact algorithm to construct sub-MAPs is not specified and is left open for alternative implementations. In this paper, we study 802.16 sub-MAPs and propose an algorithm to construct an optimal sub-MAP configuration for the given burst allocations. We show that sub-MAPs can improve the system performance by almost 25%.

Analysis of modeling styles on Network-on-Chip simulation

Abstract: This paper analyses the effects of Network-on-Chip (NoC) models written in SystemC on simulation speed. Two Register Transfer Level (RTL) models and Approximately Timed (AT) and Loosely Timed (LT) Transaction Level (TL) models are compared against reference RTL VHDL 2D mesh model. Three different mesh sizes are evaluated using a commercial simulator and OSCI SystemC reference kernel. Studied AT model achieved 13–40x speedup with modest 10% estimation error.

Registration performance comparison between IP Multimedia Subsystem and Session Initiation Protocol networks

Abstract: The IP Multimedia Subsystem (IMS) is an IP based service control framework architecture. It uses Session Initiation Protocol (SIP) to control its multimedia sessions. The IMS core can be considered as a collection of different functions that are linked with standard interfaces, forming an IMS core network. The IMS has layers for transport, the core itself, and for services and applications. The complexity of the IMS core is greater than within pure SIP based networks. To help to make comparisons between different IMS networks, the ETSI-TISPAN has unified the IMS performance measurements by defining a common framework which to follow. In this paper, the Open IMS solution by the Fraunhover Focus Institute is compared with the OpenSIPS, an open source SIP server used for user's registrations to network. The number of users was chosen to be 100 000, a large enough number to be considered as a suitable number of users for small or moderate business usage needs. Our study shows that both of the systems are able to handle this many users and, in the case of OpenSIPS, with a clear margin. It was also discovered that both systems are reliable and are suitable for small and moderate business usage and further performance study trials

Efficient WH-OFTDM signals processing

Abstract: Utilization of well-localized bases allows to improve considerably the efficiency and robustness against intercarrier interference (ICI) of now existing wireless digital communication systems based on Orthogonal Frequency Division Multiplexing (OFDM). The efficient algorithm of orthogonal well-localized finite dimensional generalized Weyl-Heisenberg (WH) basis synthesis is considered in the paper. Optimal basis parameters are proposed. Computationally efficient modulation and demodulation algorithms for signals constructed from WH bases are described. Presented modeling results confirm good bases' localization characteristics and robustness against Doppler shift. This article presents main results of research work related to the development of enhanced modulation technique with Orthogonal Time-Frequency Division Multiplexing (OFTDM).

A scalable, non-interfering, synthesizable Network-on-chip monitor

Abstract: Today's Multi-Processor System-on-Chips incorporate advanced communication mechanisms, called Network-on-Chip, to interconnect multiple resources such as processors, memories and accelerators. The detailed evaluation of these communication networks calls for low-level tools that allow detailed performance analysis at the level of the network instead of the analysis at the Processing Elements. We present a freely available toolset to perform such analysis. First level of data analysis is done on HW level on FPGA. 100Mbit/s ethernet connection is used to collect the data to host PC to be further processed and analyzed using a simple and intuitive graphical interface. Finally, we show a case study of an evaluation of an MPEG-4 encoder utilizing the NoC paradigm. We were able to compare link utilizations, stall cycles, and system performance by any time window from 500 clock cycles to the whole running time of 5 seconds at 25 MHz. The system needed to run only once, producing 43 MB of binary data with 250 000 data points, each presenting statistics for every link in the network. The total HW area overhead for monitoring was 4.8%.

Positioning in resource-constrained ultra low-power Wireless Sensor Networks

Abstract: Wireless Sensor Networks (WSNs) consist of densely deployed, independent, and collaborating low cost sensor nodes. The nodes are highly resource-constrained in terms of energy, processing, and data storage capacity. Thus, the protocols used in WSNs must be highly energy-efficient. WSN communication protocols achieving the lowest power consumption minimize radio usage by accurately synchronizing transmissions and receptions with their neighbors. In this paper, we show how network signaling frames of state-of-the-art synchronized communication protocols for low-power WSNs supporting mobile nodes can be used for positioning. We derive mathematical models for node power consumption analysis. The models provide a tool for estimating what kind of network lifetimes can be expected when average positioned node speed, the amount of anchor nodes required by the location estimation algorithm, and the location refresh rate required by the application are known. The presented analysis results are based on two kinds of node hardware: real node hardware prototypes having no Received Signal Strength Indicator (RSSI) support and typical values of an integrated chip using an IEEE 802.15.4 compliant radio with RSSI.

Class of Service Support Layer for Wireless Mesh Networks

Abstract: This paper presents an add-on Class of Service (CoS) layer for wireless mesh networks. The proposed protocol is applicable for contention-based MACs and is therefore compatible with most of the Wireless Local Area Network (WLAN) and Wireless Sensor Network (WSN) protocols. The protocol has a locally centralized control for managing data flows, which either reserve a fixed bandwidth or are weighted by fair scheduling. The protocol reduces transmission collisions, thus improving the overall throughput. IEEE 802.11 adhoc WLAN has been taken as a platform for simulations and prototyping for evaluating the protocol performance. Network Simulator Version 2 (NS2) simulations show that the CoS protocol efficiently differentiates bandwidth, supports bandwidth reservations, and reaches less than 10 ms transfer delay on IEEE 802.11b WLAN. Testing with a full prototype implementation verified the performance of the protocol.