Balint Horvath

Optimum configuration of multiloop optoelectronic oscillators

We are concerned with providing a generally applicable optimization method for harnessing the low-phase-noise microwave-millimeter-wave signal generation capabilities of optoelectronic oscillator (OEO) structures. The gained benefits include the possibility of using inexpensive, commercially available bandpass filters; single-mode operation; equidistant spacing of modes; and total cancellation of spurious content in the output signal. Our theoretical ascertainments and simulation data are underlined by numerous experimental results, which were gained through measurements on OEO setups containing one, two, or three parallel connected optical loops. This design method also makes it possible to improve the oscillators performance, obviating the need for a filter of outstanding performance, ultimately of an unreachably high Q value and low thermal sensitivity.

Evaluation of Clipping Based Iterative PAPR Reduction Techniques for FBMC Systems

This paper investigates filter bankmulticarrier (FBMC), a multicarrier modulation technique exhibiting an extremely low adjacent channel leakage ratio (ACLR) compared to conventional orthogonal frequency division multiplexing (OFDM) technique. The low ACLR of the transmitted FBMC signal makes it especially favorable in cognitive radio applications, where strict requirements are posed on out-of-band radiation. Large dynamic range resulting in high peak-to-average power ratio (PAPR) is characteristic of all sorts of multicarrier signals. The advantageous spectral properties of the high-PAPR FBMC signal are significantly degraded if nonlinearities are present in the transceiver chain. Spectral regrowth may appear, causing harmful interference in the neighboring frequency bands. This paper presents novel clipping based PAPR reduction techniques, evaluated and compared by simulations and measurements, with an emphasis on spectral aspects. The paper gives an overall comparison of PAPR reduction techniques, focusing on the reduction of the dynamic range of FBMC signals without increasing out-of-band radiation. An overview is presented on transmitter oriented techniques employing baseband clipping, which can maintain the system performance with a desired bit error rate (BER).

Calculations for the measure of the achievable phase noise reduction by the utilization of optimized multiloop opto-electronic oscillators

This paper is concerned with the analization of the real operation of optimized multiloop opto-electronic oscillator. Preceding works of the authors have proven the validity of a beneficial modification of the conventional opto-electronic oscillator (OEO) configuration. By the optimization of its multiloop structure one may easily achieve significant phase noise suppression in the output signal of the oscillator. Recent study aims for getting explicit expressions for describing this enhancement in the operation. Mathematical results are also supported by measurement results, also introduced.

Short-term stabilization of opto-electronic oscillators by multiple optical resonators

We will give a novel explanation on the mode separation and the single frequency operation of multi-loop photonic oscillators with appropriate fiber lengths and powers, supported by numerous measurements.

A new approach for ultra-low phase noise millimeterwave opto-electronic oscillators

This paper shows a new way for the enhancement of high Q - low phase noise millimeterwave opto-electronic oscillator structure. The new configuration enables us to improve the oscillators noise characteristics without the need for the utilization of especially expensive and sensitive elements (such as high Q filters, etc.).

Improving the frequency stability and phase noise of opto-electronic oscillators by harmonic feedback

Optical technology offers a new method for generating microwave signals with extremely low noise. For that purpose a long fiber is used in the feedback loop of the oscillator. However, by the application of a long fiber, a lot of resonances appear in the output spectrum impairing the stability of oscillation. This paper introduces two new approaches for improving the frequency stability and reducing the phase noise of opto-electronic oscillators. That goal is achieved in two different ways: one by the insertion of an additional third-harmonic optical loop and another by nonlinear electronic feedback techniques. This way the conversion between the fundamental and harmonic components in the nonlinear active element of the oscillator can be controlled and utilized both for improving the frequency stability and reducing the noise. The combination of these methods results in an optimum adjustment.

Architectural Design of the Q/V Band Site Diversity Experiment Between Austria and Hungary

The architectural design of the Q/V band site diversity experiment between the transmit/receive ground station in Graz/Austria and the receive only ground station in Budapest is described in this paper. The ground station Budapest is connected via Internet to transfer information about the reception quality of the received signals and to request to adjust the modulation and coding. The uplink power is controlled by the station in Graz, based on the local received beacon signal from the satellite. The planed experiments and the expected results are described in the final paragraph of this paper.

Validation of Numerical Models of Portable Wireless Devices for Near-Field Simulation

The near-field validation of the numerical models of portable wireless devices is becoming indispensable, especially, when checking SAR (specific absorption rate) compliance for regulatory limits by computer simulation. The current practice for such validation is to compare measured and simulated electromagnetic fields in a standard flat phantom. This paper proves that a cheaper and faster technique based on comparing measured and computed one-port characteristics of the antennas can equivalently accomplish the validation. The proof is based on the reciprocity theory and high-order Born approximation. The equivalence of the standard and new validation techniques is illustrated by comparing measurements and computations.

Validation of numerical models of portable wireless devices for near-field simulation

The major contribution of the paper is a theoretical proof of the equivalence between two approaches of near-field validation techniques for the numerical models of personal wireless communication devices. The current validation practice is to compare measured and computed electromagnetic field or specific absorption rate distributions. A new validation technique introduced by the authors recently compared measured and computed antenna input-impedance changes while the near field is systematically perturbed by a dielectric control object. The proof of the equivalence is based on two novel formulas derived here: a reaction impedance-change formula, and an error formula that establishes a quantitative relationship between the errors of the impedance changes and the near-field values. The equivalence of the two validation techniques is verified experimentally too by comparing measurements and computations for a planar-inverted F antenna. By performing numerical experiments for two types of printed-circuit board antennas, it is also proved here the first time that the new validation technique is feasible even if the geometric and material properties of the control object are such that the Born approximation can be introduced in the impedance-change formula.

Flat spectrum signal synthesis in filter bank multicarrier systems

Filter bank multicarrier (FBMC) modulation is a promising candidate as the primary physical layer waveform in next generation wireless networks. A great challenge in FBMC systems is channel estimation. A solution to this problem is preamble based channel estimation. In this paper we derive conditions for flat spectrum FBMC preamble construction. This kind of preamble offers simple, fast Fourier transform based channel estimation in the receiver. The paper also presents an example pilot preamble which fulfils the derived conditions.