Tomislav Švedek

A Method for the Schmitt-Trigger Propagation-Delay Compensation in Asynchronous Sigma–Delta Modulator

This brief provides the mathematical analysis of the Schmitt-trigger propagation-delay influence on the asynchronous sigma-delta modulator (ASDM) output-signal frequency spectrum. Beside the propagation delay, the Schmitt-trigger slew-rate impact has been also presented. Based on the mathematical analysis, a method for the Schmitt-trigger propagation-delay compensation has been proposed. The method is implemented by introducing hysteresis-level modulation. The first-order ASDM simulation and measurement models have been proposed for the propagation-delay influence to the ASDM output-signal frequency and for the compensation method verification. The measurement and simulation results for the proposed method confirm the ASDM output frequency spectrum improvement.

Pulse interval modulation for ultra-high speed IR-UWB communications systems

This paper analyzes performances of the Pulse Interval Modulation (PIM) scheme for impulse radio ultra-wideband (IR-UWB) communication systems. Due to the PIM anisochronous nature, a tap delay line (TDL) coded division multiple access (CDMA) scheme based on strict optical orthogonal codes (SOOC) is proposed. This scheme is suitable for multiuser high-speed data asynchronous transmission applications because the average symbol length is shorter than in Pulse Position Modulation (PPM) schemes and it needs only chip synchronization. The error probability over the additive white Gaussian noise (AWGN) channel is derived in the single- and multi-user environment and compared with other modulation schemes.

Limit cycle frequency jittering of an asynchronous sigma-delta modulator

This paper presents limit cycle frequency jittering of a first order Asynchronous Sigma-Delta Modulator (ASDM) implemented with Schmitt trigger. Particular interest is placed on a jitter of a Schmitt trigger hysteresis voltage (hysteresis jitter). Hysteresis jitter has been modeled in MATLAB® Simulink and the model simulation has been compared with measurements for first ordered ASDM. Both simulation and measurement show that ASDM model limit cycle frequency depends on the hysteresis jitter.

Performance of hybrid pulse shape amplitude modulation for UWB communications systems over multipath channels

This paper describes a hybrid pulse shape amplitude modulation (PSAM) scheme for time hopping ultrawideband (TH-UWB) communication system, which is the combination of pulse amplitude modulation (PAM) and pulse shape modulation (PSM) based on modified Hermite pulses (MHP). This scheme is suitable for high rate data transmission applications because b=log2(MN) bits can be mapped with one waveform. The system performance over multipath channel is derived in the single- and mult-user environment.

Business models and cost optimization of wireless rural broadband access implementation

Aiming at the reduction of the existing digital gap between many rural and urban european areas as well as at the optimization of the rural broadband access deployment costs, several rural broadband deployment cases in the Republic of Croatia are compared in this paper. The comparison is conducted from the business and the regulatory point of view, and the possibilities of the cost-effective solutions for rural broadband access implementation are evaluated. The advantages of wireless over wired access are taken into account. Hence, wireless WiMAX broadband access implementation is analyzed in the paper. In order to foster further broadband implementation in rural areas and to point on the possible cost-effectiveness of wireless broadband access deployments in Croatian rural areas, the given results help in choosing the optimized wireless access solutions for the given rural scenarios.

An analog multiplier based on asynchronous sigma-delta pulse amplitude modulation

Asynchronous sigma-delta modulation (ASDM) has been proposed as a possible solution for the amplitude to duty-cycle conversion. The information conveyed by voltage level of the ASDM input signal is converted into the duty cycle of the ASDM output signal period. Applying pulse amplitude modulation (PAM) to ASDM output pulse stream, 2-input analog multiplier can be obtained. The mean value of the output pulse stream period corresponds to the product of the ASDM input and PAM input signals. This paper gives the mathematical analysis of the ASDM-PAM analog multiplier output signal spectrum for the DC and sinusoidal input signals. It has been shown that combination of ASDM and PAM modulation generates a product of the two input signals in the baseband and around multiples of the central frequency, which can be later on efficiently filtered out. The ASDM-PAM multiplier Simulink model has been used for confirmation of the mathematical analysis.

Walsh function synthesis of the combined multiple shift-keyed modulated signals

Introduction of redundancy in modulation of shift-keyed signals by combining phase, frequency and/or amplitude information elements, can increase their detection probability. To make receiving side measurements for evaluation of detection probability and spectral occupancy penalty it is necessary to build a flexible, but simple for realization, modulator by which all combinations of the shift-keyed signals can be easily synthesized. The paper introduces the Walsh function based generator for synthesis of the combined multiple shift-keyed signals: M/sub P/-PSK/M/sub F/-FSK, M/sub P/-PSK/M/sub P/-ASK, PSK/M/sub A/-ASK, and M/sub F/-PSK/M/sub A/-FSK/M/sub A/-ASK. The proposed generation technique is chosen because the generator can be realized digitally in the small ROM-less PLD with a small number of components outside of the chip. The core of the generator is synthesis of the sine-wave carrier by Walsh functions. This synthesized carrier is modulated by a digital signal, producing single or combined shift-keyed modulated signals. Frequency modulation is achieved by a change of input clock frequency, discrete phase shifts are synthesized within a generator by the special shift-functions set, and discrete amplitude elements are obtained from the attached gain control amplifier. The generator is realized digitally in low complexity PLD, with a D/A conversion weighted resistor network and gain control amplifier outside of the chip. The paper presents oscillograms and power spectrum for the two combined multiple shift-keyed modulated signals.

Integrator clamping for asynchronous sigma-delta modulator central frequency increment

Hysteretic comparator (Schmitt trigger) is the basic part of the asynchronous sigma-delta modulator (ASDM). If propagation delay of a hysteretic comparator is not equal to zero and it has measurable value, than it affects the ASDM output frequency spectrum. As ASDM is a circuit with serial connection of an integrator and a hysteretic comparator followed by a negative feedback loop, propagation delay of the comparator will introduce the timing errors in ASDM output signal-triggering events. Therefore ASDM central frequency will be lower then it is in the case for propagation delay equal to zero. This study provides mathematical analysis of the hysteretic comparator propagation delay influence to the ASDM output frequency spectrum. The method for ASDM central frequency improvement using integrator voltage clamping has been proposed. Mathematical analysis, together with simulation and measurement results, shows partial central frequency increment. As ASDM circuit can be used as an oscillator for zero-input signals, central frequency improvement can be significant.

Optimal Multi Pulse Position Modulation for TH-IR-UWB communication systems

In this paper an optimal Multi Pulse Position Modulation (OMPPM) scheme for time-hopping impulse radio ultra-wideband (TH-IR-UWB) communication systems is proposed. OMPPM is modified version of MPPM in which the information is conveyed by the position of w pulses, each within their own frame of N positions, giving Nw OMPPM symbols. The influence of different modulation parameters is analyzed and proposed scheme is compared with PPM and PAM over IEEE 802.153a channel model. It is shown that OMPPM has higher bandwidth efficiency then PPM, and lower circuit complexity than MPPM.

Accurate Analytical Multiple-Access Performance of Time-Hopping Biorthogonal PPM IR-UWB Systems

In this paper, the characteristic function (CF) method is used to derive the symbol error rate (SER) expression for time-hopping impulse radio ultra–wideband (TH-IR-UWB) systems with a biorthogonal pulse position modulation (BPPM) scheme in the presence of a multi-user interference (MUI). The derived expression is validated with the Monte-Carlo simulation and compared with orthogonal PPM. Moreover, the analytical results are compared with the Gaussian approximation (GA) of MUI which is shown to be inaccurate for a medium and large signal-to-noise ratio (SNR). It is also shown that the BPPM scheme outperforms the PPM scheme for all SNR. At the end, the influence of different system parameters on the BPPM performance is analyzed.