Mario Huemer

Key generation based on acceleration data of shaking processes

Hard restrictions in computing power and energy consumption favour symmetric key methods to encrypt the communication in wireless body area networks which in term impose questions on effective and user-friendly unobtrusive ways for key distribution. In this paper, we present a novel approach to establish a secure connection between two devices by shaking them together. Instead of distributing or exchanging a key, the devices independently generate a key from the measured acceleration data by appropriate signal processing methods. Exhaustive practical experiments based on acceleration data gathered from real hardware prototypes have shown that in about 80% of the cases, a common key can be successfully generated. The average entropy of these generated keys exceed 13bits.

Modeling, Control, and Implementation of DC–DC Converters for Variable Frequency Operation

In this paper, novel small-signal averaged models for dc-dc converters operating at variable switching frequency are derived. This is achieved by separately considering the on-time and the off-time of the switching period. The derivation is shown in detail for a synchronous buck converter and the model for a boost converter is also presented. The model for the buck converter is then used for the design of two digital feedback controllers, which exploit the additional insight in the converter dynamics. First, a digital multiloop PID controller is implemented, where the design is based on loop-shaping of the proposed frequency-domain transfer functions. And second, the design and the implementation of a digital LQG state-feedback controller, based on the proposed time-domain state-space model, is presented for the same converter topology. Experimental results are given for the digital multiloop PID controller integrated on an application-specified integrated circuit in a 0.13 μm CMOS technology, as well as for the state-feedback controller implemented on an FPGA. Tight output voltage regulation and an excellent dynamic performance is achieved, as the dynamics of the converter under variable frequency operation are considered during the design of both implementations.

Spread spectrum communications using chirp signals

We report on the use of broadband chirp signals for spread spectrum systems in indoor applications. The presented system concepts make use of chirp transmission and pulse compression. Different modulation schemes for the chirp signals resulting in different system performance and complexity are compared in terms of bit error rate for the AWGN channel and for frequency selective indoor radio channels. We present simulations and measurement results from demonstrator systems which use surface acoustic wave (SAW) devices for the generation and matched altering of the chirp signals. The RF and IF frequency and transmission bandwidth of the presented systems are 2.4 GHz, 348.8 MHz, and 80 MHz, respectively. Due to the processing gain of 16 dB-made possible by the use of SAW devices-and the large transmission bandwidth the system is insensitive against frequency selective fading, CW interference and noise.

A different look on cyclic prefix for SC/FDE

We investigate the use of a known symbol sequence - a so-called unique word (UW) - instead of the well-known cyclic prefix (as it is used in OFDM, orthogonal frequency division multiplexing, systems) for a single carrier system with frequency domain equalization (SC/FDE). The considered SC/FDE system is similar to the one proposed in the IEEE 802.16.3c target group. It is shown that the UW fulfils the theorem of cyclic convolution required for efficient implementation of the SC/FDE structure. We elaborate on the advantages that result for equalization, channel estimation, and synchronisation. Compared to the advantages, the disadvantages in terms of BER behaviour and bandwidth efficiency are rather modest.

A Wireless Charging System Applying Phase-Shift and Amplitude Control to Maximize Efficiency and Extractable Power

Wireless power transfer (WPT) is an emerging technology with an increasing number of potential applications to transfer power from a transmitter to a mobile receiver over a relatively large air gap. However, its widespread application is hampered due to the relatively low efficiency of current Wireless power transfer (WPT) systems. This study presents a concept to maximize the efficiency as well as to increase the amount of extractable power of a WPT system operating in nonresonant operation. The proposed method is based on actively modifying the equivalent secondary-side load impedance by controlling the phase-shift of the active rectifier and its output voltage level. The presented hardware prototype represents a complete wireless charging system, including a dc-dc converter which is used to charge a battery at the output of the system. Experimental results are shown for the proposed concept in comparison to a conventional synchronous rectification approach. The presented optimization method clearly outperforms state-of-the-art solutions in terms of efficiency and extractable power.

Unique word based phase tracking algorithms for SC/FDE-systems

In this paper we consider phase tracking algorithms for single carrier systems with frequency domain equalizers (SC/FDE), which make use of the concept of unique word (UW) blockwise extension instead of the classical concept of cyclic prefix (CP) like it is used for example in OFDM (orthogonal frequency division multiplexing). Very similar to IEEE 802.11a like OFDM systems the overall baseband processing performance of SC/FDE systems largely depends on the design of channel estimation and synchronization algorithms. Some of the synchronization tasks are very straight forward, but the algorithm developer has a lot of freedom for the design of the channel estimator, and for the design of the residual carrier frequency offset tracking procedure (which we call phase tracking). In this paper we focus on the design and performance of unique word based phase tracking algorithms, which are being compared with pilot carrier based phase tracking algorithms for IEEE 802.11a like OFDM systems.

Non-Systematic Complex Number RS Coded OFDM by Unique Word Prefix

In this paper, we expand our recently introduced concept of unique word orthogonal frequency division multiplexing (UW-OFDM). In UW-OFDM the cyclic prefixes (CPs) are replaced by deterministic sequences, the so-called unique words (UWs). The UWs are generated by appropriately loading a set of redundant subcarriers. By that a systematic complex number Reed-Solomon (RS) code construction is introduced in a quite natural way, because an RS code may be defined as the set of vectors, for which a block of successive zeros occurs in the other domain w.r.t. a discrete Fourier transform. (For a fixed block different to zero, i.e., a UW, a coset code of an RS code is generated.) A remaining problem in the original systematic coded UW-OFDM concept is the fact that the redundant subcarrier symbols disproportionately contribute to the mean OFDM symbol energy. In this paper we introduce the concept of non-systematic coded UW-OFDM, where the redundancy is no longer allocated to dedicated subcarriers, but distributed over all subcarriers. We derive optimum complex valued code generator matrices matched to the best linear unbiased estimator (BLUE) and to the linear minimum mean square error (LMMSE) data estimator, respectively. With the help of simulations we highlight the advantageous spectral properties and the superior bit error ratio (BER) performance of non-systematic coded UW-OFDM compared to systematic coded UW-OFDM and to CP-OFDM in additive white Gaussian noise (AWGN ) as well as in frequency selective environments.

A wireless spread-spectrum communication system using SAW chirped delay lines

We report on the use of broad-band chirp signals for spread-spectrum communications in indoor and industrial environments. The well-known pulse compression technique associated with chirp signals is exploited to achieve a highly robust communication system. For the generation and compression of the chirp signals, surface acoustic wave delay lines fabricated from an LiTaO/sub 3/-X112rotY substrate are used. Center frequency, bandwidth, chirp duration, and chirp rate are 348.8 MHz, 80 MHz, 500 ns, and /spl plusmn/40 MHz//spl mu/s, respectively. Different modulation schemes for chirp signals are introduced, the effects of nonlinearities, frequency drift, and temperature drift are addressed, and simulations and measurement results from a hardware demonstrator are presented for the use of /spl pi//4-differential quadrature phase-shift keying (DQPSK) modulation. A data rate of up to 40 Mb/s has been achieved experimentally and shows that the proposed system is highly robust against multipath effects.

A robust ultra broadband wireless communication system using SAW chirped delay lines

The present invention provides an improved grade of polyimide containing an organic phosphorus compound, a film composed thereof and a method of making the aforementioned film. According to the present invention, it is possible to obtain a polyimide film improved in mechanical strength.

A robust ultra-broad-band wireless communication system using SAW chirped delay lines

Design and performance of SAW chirped delay lines on LiTaO/sub 3/-X112rotY for a wireless communication system are presented. Center frequency, bandwidth and chirp rate are 350 MHz, 80 MHz, and /spl plusmn/20 MHz/s, respectively. An optimized square-root weighting was chosen to reduce the sidelobes of the compressed pulse to -42 dB compared to the correlation peak. The chirp filters have been deployed in a hardware demonstrator for a wireless indoor communication system for data rates of a few Mbit/s. Limiting factors for the data rate according to simulations and measurements are mainly the intersymbol interference due to the time-overlapping of consecutive symbols and to a lesser extent the multipath propagation.