Papers by Grigorios Kalivas
John Wiley & Sons, Ltd eBooks, Dec 12, 2009
International Conference on Networking, International Conference on Systems and International Conference on Mobile Communications and Learning Technologies (ICNICONSMCL'06)
Orthogonal Frequency Division Multiplexing (OFDM) is a promising approach to achieve higher data ... more Orthogonal Frequency Division Multiplexing (OFDM) is a promising approach to achieve higher data rates with sufficient performance. However a measure of channel state is desired in order to decide upon transition to these rates. Signal-to-Noise Ratio (S1NR) is such a measure and an estimator operating in low transmission rates, such as BPSK or using the preamble data would be proper. In this work two online SNR estimators are developed for OFDM systems, operating on BPSK modulation or on the preamble data. It is shown that the convergence of the algorithms to the actual SNR value is achieved from about 0 dBs or even lower. The impact of the channel estimation used on the SNR estimation accuracy is given and improvements, regarding the computational cost, on one of them are given. Finally a transmission procedure for an OFDM modem using these SNR estimators is given.
Symposium on Antenna Technology and Applied Electromagnetics, Aug 1, 1994
This paper focuses on the design of an indoor broadband radio system at 29 GHz with some emphasis... more This paper focuses on the design of an indoor broadband radio system at 29 GHz with some emphasis on the effect of antennas on the availability of the system, for various cell sizes. The system has a maximum information bit rate of 155 Mb/sec and a maximum receiver noise figure of 8 dB. Channel measurements with antenna diversity were carried out during an earlier stage of the project at 2L6 GHz and 37.2 GHz. The resulting characterization provided knowledge of the parameters needed to evaluate the performance of the link. These included large-scale path-loss models which gave estimates of the power-law exponents and statistics of the received envelope. Transceiver characteristics and measured channel behavior as outlined above along with the different antenna types (omnidirectional and horn) and different antenna orientations determine the distribution of the received power across the cell, and thus the average availability. Practical configurations were investigated involving partial alignment or no alignment of the base station and portable antennas. Full antenna alignment was also examined for the purpose of comparison.
Electronics Letters, 2010
A fully differential sub-harmonic injection-locked phase-locked loop (PLL) that achieves improved... more A fully differential sub-harmonic injection-locked phase-locked loop (PLL) that achieves improved levels of phase noise performance through the incorporation of injection locking and fully differential architecture is presented. Details concerning the design of each building block are given and the corresponding simulation results are presented. The system level architecture exploration is introduced together with the phase noise analysis. A physical implementation of the proposed design using a standard 0.5 mm SiGe BiCMOS process is also presented as a case study in order to prove the functionality as well as the overall performance. Phase noise improvement is 20 dB at 1 kHz when a sub-harmonic of the free-running oscillation frequency at 2.5 GHz with a 215 dBm power level is injected.
ABSTRACT First Page of the Article
2006 8th International Conference Advanced Communication Technology, 2006
In this paper we propose a novel blind TRMS estimator for wireless orthogonal frequency division ... more In this paper we propose a novel blind TRMS estimator for wireless orthogonal frequency division multiplexed (OFDM) systems, that can be used for channel estimation. The estimator is based on the frequency correlation between subcarriers of one OFDM symbol and an expression between frequency correlation and TRMS is derived assuming an exponentially decaying power delay profile (PDP). The estimation performance,
This paper presents a 30 GHz Low Noise Amplifier (LNA) in 28nm FD-SOI CMOS technology for 5G appl... more This paper presents a 30 GHz Low Noise Amplifier (LNA) in 28nm FD-SOI CMOS technology for 5G applications. The LNA consists of two stages. The first stage is a cascode topology with gm-boosting technique in order to achieve low Noise Figure (NF). The second stage consists of a differential amplifier for the purpose of achieving higher gain. The first and second stages are coupled, using a balun (balanced to unbalanced) transformer. The proposed LNA exhibits a gain of 24.1 dB and the minimum NF of 3.7 dB at 30 GHz. This specific LNA design consumes only 9.3 mW from a power supply of 1V.
International Journal of Circuit Theory and Applications, 2010
A linear, Ultra Wideband, low‐power VCO, suitable for UWB‐FM applications is proposed, forming th... more A linear, Ultra Wideband, low‐power VCO, suitable for UWB‐FM applications is proposed, forming the main part of a UWB‐FM transmitter. The VCO is designed in TSMC 90thinspacenm digital CMOS process and includes a Source‐Coupled Multivibrator, used as current‐controlled oscillator (CCO) which generates output frequencies between 2.1 and 5 GHz and a voltage‐to‐current (V‐to‐I) converter which translates the VCO input voltage modulation signal to current. Two single‐ended inverter buffers are employed to drive either a differential or a single‐ended UWB antenna. The presented VCO is designed for 1 V power supply and exhibits a linear tuning range of 2.1–5 GHz, a differential output power of −7.83 dBm±0.78 dB and low power consumption of 8.26 mW, including the output buffers, at the maximum oscillation frequency. It is optimized for a very high ratio of tuning range (81.69%) over power consumption equal to 9.95 dB. The desired frequency band of 3.1–5 GHz for UWB‐FM applications is covered for the entire industrial temperature range (−40 to 125∘C). Copyright © 2010 John Wiley & Sons, Ltd.
ABSTRACT Signal-to-noise ratio (SNR) is an important parameter for adaptive orthogonal frequency ... more ABSTRACT Signal-to-noise ratio (SNR) is an important parameter for adaptive orthogonal frequency division multiplexing (OFDM) systems as it serves as a standard measure of signal quality. In this work, we present a novel SNR per subcarrier estimation scheme for wireless OFDM systems in frequency selective channels. The novel scheme can operate both in time and frequency, requiring only one previously known OFDM symbol. Firstly the noise variance per subcarrier estimate is obtained using the estimated channel coefficients and a novel analysis of its estimation error is provided. The noise variance per subcarrier estimate is used to obtain the SNR per subcarrier estimate. The estimation scheme takes under consideration the frequency selectivity of the channel and the variation of the noise statistics across the OFDM subcarrier index. The estimator's performance, in means of normalized mean square error (NMSE), is evaluated through simulations on a variety of channel models and is compared with another estimation scheme. The NMSE of the proposed scheme demonstrates its ability to identify the local statistics of the noise efficiently resulting into a reliable estimator in contrast with other similar approaches.
A subharmonic injection-locked self-oscillating mixer (s-ILSOM) at 1 GHz is reported in this pape... more A subharmonic injection-locked self-oscillating mixer (s-ILSOM) at 1 GHz is reported in this paper. The proposed circuit which combines both injection-locking and mixing functions is described theoretically and experimentally. In contrast to previously reported works, only one input port is required for both the RF/IF signal and the injection signal. Furthermore, the injection signal which is used to stabilize the oscillation is at a subharmonic of the oscillation frequency (fLO/4), with a power level as low as -20 dBm. Phase noise calculations and mixing characteristics are reported, indicating a noise improvement, and a high up-conversion gain for both fundamental and harmonic mixing. The circuit is implemented, using a GaAs FET, exhibiting an up-conversion gain of 13 dB, a phase noise of -93 dBc/Hz at 100 KHz offset, a P1dB of -18 dBm, an IP3 of -5 dBm, and a power consumption of 24 mW.
Microwave and Optical Technology Letters, 2005
In this paper, we introduce a 5-GHz injection-locked phase-locked loop (ILPLL). A new method is p... more In this paper, we introduce a 5-GHz injection-locked phase-locked loop (ILPLL). A new method is presented for accurate analysis of the phase-noise performance of the proposed system. Furthermore, comparison with other phase-noise-estimation techniques demonstrates that our method provides an accurate characterization of any ILPLL topology. The theoretical and calculation results show an improved performance for phase noise, locking range, and power consumption compared to conventional phase-locked loops (PLLs) and injection-locked oscillators (ILOs). Furthermore, we demonstrate the pulling behavior of the injected oscillator and examine the obtained results. To verify the presented analysis, a 5-GHz prototype has been implemented, which achieves Ϫ119-dBc/Hz at 100-KHz frequency offset, producing ϩ4.5 dBm of output power and consuming 9 mA at 3 V.
European Wireless Conference, Apr 2, 2006
ABSTRACT Signal-to-Noise Ratio (SNR) is an important parameter in many receivers to improve their... more ABSTRACT Signal-to-Noise Ratio (SNR) is an important parameter in many receivers to improve their performance. In this paper, we develop a modified Error Vector Magnitude (mEVM) SNR estimation algorithm for Orthogonal Frequency Division Multiplexed (OFDM) systems in Additive White Gaussian Noise (AWGN) channels. At first mEVM is introduced for QPSK modulation. We also generalize the idea to 16- and 64-QAM modulation using two groups of selected data: data representing a specific single constellation point and data belonging to a group (up to 4) of neighboring constellation points. Criteria used to measure its performance are the SNR estimation accuracy compared to the actual SNR, the variance of the estimation and the mean square error (MSE). Computer simulations show that the proposed estimator for both types of data selection at SNR values of practical interest for each modulation type is highly accurate and reliable for OFDM systems, outperforming previously published generic QPSK SNR estimators. Finally the impact of the channel estimation method used to improve signal¿s reception, on the SNR estimation accuracy is examined.
IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control, Sep 1, 1991
The current demand for FH-SS or hybrid SS communications systems creates a need for the developme... more The current demand for FH-SS or hybrid SS communications systems creates a need for the development of increasingly fast and accurate frequency-hopped synthesizers. The characterization of these frequency-hopped synthesizers has conventionally been done using frequency-domain methods. A method that applies time-domain stability measures is introduced, hitherto used only in the context of fixed-frequency sources, to the characterization of frequency-hopped sources. This new method has been successfully applied to the testing of a novel practical frequency-hopping synthesizer.
This paper presents a (transceiver) TRX front-end structure design for Phased Array applications ... more This paper presents a (transceiver) TRX front-end structure design for Phased Array applications in 40nm CMOS Bulk process. The proposed structure consists of the Power Amplifier (PA) the Low Noise Amplifier (LNA) along with a monolithic transformer duplexer for Antenna connection applied in half-duplex systems. The front end covers the millimeter wave (MMW) 5G band. The PA design contains two differential cascode stages with capacitor neutralization technique achieving a small signal gain (S21) of 22.86dB with a -3dB bandwidth (BW) at 22-34 GHz. Moreover, the PA reaches a PAEmax of 31.66% and a Psat of 18.5 dBm. The LNA design consist of two cascode stages using current reuse technique at the first stage, obtaining 17.5 dB gain (S21) with a -3 dB bandwidth from 22.5 to 31 GHz. Both amplifiers are connected to the antenna through a compact duplexer with minimum losses and sufficient isolation.
IEEE Transactions on Microwave Theory and Techniques, Dec 1, 1984
ABSTRACT A technique is described which removes a major difficulty in the design of wide-band fre... more ABSTRACT A technique is described which removes a major difficulty in the design of wide-band frequency-halving networks: the accurate characterization of the "pumped" input output impedances at the plane of the varactors. The procedure permits the use of realistic input, output power levels with the input at twice the output frequency.
In this paper the implementation of a low complexity Rake Receiver (RR) and Channel Estimator (CE... more In this paper the implementation of a low complexity Rake Receiver (RR) and Channel Estimator (CE) for Direct Sequence Spread Spectrum (DSSS) systems is presented with main scope to provide adaptability in receiver parameters while keeping the complexity at low levels. The trend in communication systems is towards dynamically adjusting system implementations that can adapt their structure to the continuously changing transmission characteristics. Following this trend we propose an architecture that is based on the spreading factor of the system, which controls the number of the taps that the CE and the RR will use depending on the current channel conditions. Moreover, based on a resource sharing approach of the main system components, that yet meets the standard bit rates, low complexity is achieved avoiding otherwise necessary complex structures such as complex multipliers. Furthermore we implement the proposed system on FPGA that gives us the ability to measure performance in terms of Bit Error Rate (BER) in addition to that of power dissipation and area. Thus the performance of the system is compared with the performance of a high level system simulation of the same system, accomplishing the same BER levels. Finally the system implemented on a Xilinx Spartan-3 MB board occupies 56% of the total slices and consumes 103.45mW with a 5V supply. I.
International Journal of Circuit Theory and Applications, Apr 1, 2009
ABSTRACT Subharmonic injection-locking and self-oscillating mixing functions of a modified Colpit... more ABSTRACT Subharmonic injection-locking and self-oscillating mixing functions of a modified Colpitts oscillator operating at 1 GHz are reported. The injection-locking circuit, using a GaAs FET, is described theoretically and experimentally. Phase noise, power consumption and conversion gain measurements indicate that the proposed design is attractive for low-cost, low-power consumption front-ends. Copyright © 2008 John Wiley & Sons, Ltd.
ABSTRACT Vehicular Network is becoming increasingly popular in recent years, Vehicle-to-Vehicle (... more ABSTRACT Vehicular Network is becoming increasingly popular in recent years, Vehicle-to-Vehicle (V2V) and Vehicle-to-Infrastructure (V2I) mobile communication mode can provide great variety of feasible applications. This paper provides the architecture design of a vehicular WiMAX-WLAN network proposed for surveillance implementations on railway environment. Mainly we focus on data transmission applications over V2I communications during fast handover procedure. For this reason we analyze the proposed IEEE 802.16e-802.11b/g/earchitecture for Vehicle-to-Infrastructure between two oncoming trains while moving in opposite directions with constant speeds during fast handover procedure. Finally, through OMNeT++simulator tool we evaluate the performance metrics of the vehicular wireless network simulation results based on handover performance.
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Papers by Grigorios Kalivas