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Intra-Vehicular Wireless Sensor Networks

Final Report Summary - IVWSN (Intra-Vehicular Wireless Sensor Networks)

Since the number of powerful electronic control units (ECU) and associated distributed sensor and actuator components inside the car keeps increasing every year, the manufacturing and installation of wiring harnesses for transmission of data and power for all these components require considerable engineering effort. Eliminating the wires can potentially provide part cost savings, assembly and maintenance savings, fuel efficiency due to decreased weight and flexibility to accommodate the growing demand for on-board sensors without adding physical capacity. Moreover, wireless sensing enables new sensor technologies to be integrated into vehicles, which would otherwise be impossible using wired means, such as Intelligent Tire. The deployment of iIntra-Vehicular Wireless Sensor Networks (IVWSN) highly depends on whether they can provide the same performance and reliability as that offered by wiring system in transmitting real-time sensing data. The communication protocol design for such a network is extremely challenging due to the strict application requirements for reliability, delay, size and weight in a highly dynamical environment with very limited available energy. This project aims to build an experimental platform to measure and analyze the physical layer channel characteristics at different sensor locations within the vehicle and develop a methodological approach to the medium access control protocol design for IVWSN.

Investigation of different modulation strategies including Radio-Frequency Identification (RFID), narrowband, spread spectrum and ultra-wideband (UWB) for IVWSN in the literature demonstrated that UWB is the most suitable technology satisfying high reliability requirement of vehicle control systems and strict energy efficiency requirement of the sensor nodes at short distance and low cost in such harsh environment containing a large number of reflectors operating at extreme temperatures. Most UWB channel measurement campaigns have been performed in such locations as indoor, outdoor, around the human body or industrial environments. The vehicular environment however is very different from these environments due to short distances, dense multipath and lack of line of sight from most sensors to the corresponding ECU. The channel modeling efforts in intra-vehicle environments on the other hand either concentrate on the passenger compartment or the trunk, which is not the typical place where vehicle sensors are located, or provide measurement results for a limited number of sensor locations beneath the chassis or within the engine compartment, which is not enough to provide a detailed model for intra-vehicular sensors. Moreover, none of the previous UWB channel measurements aim to model small-scale fading: Small-scale fading is defined as the changes in power delay profile caused by small changes in transmitter and receiver position while environment around them does not change significantly in contrast to the large-scale fading that models the changes in received signal when the position of the transmitter or receiver varies over a significant fraction of distance between them and/or environment around them changes.
For the physical layer modeling, we analyzed the small-scale and large-scale statistics of the UWB channel beneath the chassis and within the engine compartment of the vehicle. Collecting extensive amount of data allowed us to both improve the accuracy of the large-scale fading representation and model small-scale fading characteristics. The parameters are derived for path loss, power variation around the path loss, general shape of the impulse response characterized by a modified Saleh-Valenzuela (SV) model and small-scale fading for four different scenarios: Fiat Linea engine off, Fiat Linea engine on, Peugeot Bipper engine off and Fiat Linea driven on the road. The detailed algorithm for generating the channel model, the analysis of small-scale fading characteristics and effect of moving vehicle on the large-scale and small-scale parameters have been investigated for the first time in the literature.

For the medium access control layer, we studied optimal power control, rate adaptation and scheduling for UWB-based IVWSNs extensively. The close interaction of communication with control systems, very high reliability, strict energy efficiency and delay requirements in such harsh environment are distinguishing properties of this network. A novel scheduling problem has been formulated to provide maximum level of adaptivity accommodating the changes in transmission time, retransmissions due to packet losses and allocation of additional messages while meeting the packet generation period, transmission delay, reliability and energy requirements of the sensor nodes varying over a wide range. The mathematical formulation of the optimization problem and heuristic algorithms have been developed for one-ECU and multiple-ECU cases: For one ECU case, we show that the optimal rate and power allocation is independent of the optimal scheduling algorithm. We prove the NP-hardness of the scheduling problem and formulate the optimal solution as a Mixed Integer Linear Programming (MILP) problem. We then propose a 2-approximation algorithm, Smallest Period into Shortest Subframe First (SSF) algorithm. For the multiple ECU case where the concurrent transmission of the links is allowed, we formulate optimal power control as a Geometric Programming (GP) problem and optimal scheduling problem as a MILP problem where the number of variables is exponential in the number of the links. We then propose a heuristic algorithm, Maximum Utility based Concurrency Allowance (MUCA) algorithm, based on the idea of improving the performance of the SSF Algorithm significantly in the existence of multiple ECUs by determining the sets of maximum utility. The ideas of UWB based scheduling for IVWSN have also been generalized for UWB based ad hoc networks, rate adaptive packet based networks, general wireless networked control systems and duty cycle based networks.

contact: Sinem Coleri Ergen
Assistant Professor
Electrical and Electronics Engineering
Koc University
Rumeli Feneri Yolu, Sariyer, Istanbul, 34450
email: sergen@ku.edu.tr
webpage: http://home.ku.edu.tr/~sergen/