Grigorios Kalivas

SNR Estimation for Low Bit Rate OFDM Systems in AWGN Channel

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.

Radio channel characterization in industrial environments and spread spectrum modem performance

In this work the characteristics of the radio channel of a typical industrial environment are examined in detail by means of experimental measurements. The channel impulse response is measured at several representative positions. These measurements are then used to calculate important propagation parameters like attenuation, rms delay spread and coherence bandwidth. Furthermore, directional antennas are used to investigate the effect of directional transmission in propagation parameters. Finally, the performance of direct sequence spread spectrum (DSSS) radio transmission (in the 2.4 GHz band) is evaluated for omnidirectional and directional reception by means of bit error rate (BER) measurements at the same characterized positions

A 5-GHz Subharmonic Injection-Locked Oscillator and Self-Oscillating Mixer

This paper presents a multifunctional circuit realizing the functions of oscillation, mixing, amplification, and frequency multiplication at 5 GHz. A theoretical and experimental description of the circuit is given. The proposed circuit, which combines both the injection-locking and mixing processes, uses only one port where both the RF/intermediate frequency signal and the injection signal (IS) are applied. The IS, which is used to stabilize the oscillation, is at a subharmonic of the oscillation frequency (omegaosc/4) having a power level as low as -50 dBm. Calculations of the phase noise and measurements of the mixing properties are reported which indicate a noise improvement, and a high up-conversion gain. The implementation of the circuit exhibits an up-conversion gain of 14 dB, a phase noise of -110 dBc/Hz at 100-kHz offset, a dB of -15 dBm, a third-order intercept point of -2 dBm, and a power consumption of 35 mW. Calculated and measured results are in good agreement for all cases, emphasizing the relevance of the proposed circuit.

Delay performance of radio physical layer technologies as candidates for wireless extensions to industrial networks

The benefits of wireless extensions in industrial networks are well recognized as long as the integration of the wireless and fieldbus domains will be capable to offer the realtime and dependability quality of the current wired industrial networking solutions. This paper presents a study, from a performance point of view, for the possible integration of the most popular 3G and WLAN radio technologies with fieldbus technologies. A brief examination of a number of dominant wireless protocols against the basic wireless fieldbus requirements is presented. For the case study, Profibus is used, on which, the basic message cycle performance is calculated for each of the UNITS, 802.11b and HIPERLAN protocols, under different integration approaches.

A sub-1V supply CMOS voltage reference generator

An integrated sub-1V voltage reference generator, designed in standard 90-nm CMOS technology, is presented in this paper. The proposed voltage reference circuit consists of a conventional bandgap core based on the use of p-n-p substrate vertical bipolar devices and a voltage-to-current converter. The former produces a current with a positive temperature coefficient (TC), whereas the latter translates the emitter-base voltage of the core p-n-p bipolar device to a current with a negative TC. The circuit includes two operational amplifiers with a rail-to-rail output stage for enabling stable and robust operation overall process and supply voltage variations while it employs a total resistance of less than 600 K Ω. Detailed analysis is presented to demonstrate that the proposed circuit technique enables die area reduction. The presented voltage reference generator exhibits a PSRR of 52.78 dB and a TC of 23.66ppm/∘C in the range of − 40 and 125∘C at the typical corner case at 1 V. The output reference voltage of 510 mV achieves a total absolute variation of ± 3.3% overall process and supply voltage variations and a total standard deviation, σ, of 4.5 mV, respectively, in the temperature range of − 36 and 125∘C. Copyright

Locking techniques for RF oscillators at 5-6 GHz frequency range

This work aims at analyzing three different techniques for synchronizing RF oscillators. These techniques are Injection Locking (ILO), Phase Locked Loop (PLL) and Injection Locked Phase Locked Loop (ILPLL). ILPLL, which is a combination of PLL and ILO, has superior noise performance -compared to all the rest- at medium frequency offsets and the same noise performance at low and high offsets. Furthermore, the ILPLL has better locking range and lower phase noise than the ILO for phase-shifts close to /spl plusmn/90/spl deg/. In this work we present two different approaches for the study of the performance of the ILPLL, which as we show, produce equivalent results concerning the noise. A common gate VCO was used and the injected signal was the same for comparison reasons.

Heterogeneous hybrid vehicular WiMAX-WiFi network for in-tunnel surveillance implementations

Hybrid wireless networks have been identified as a promising solution to establish communication over vehicular systems that can overcome the current and future needs for increasing public safety and efficiency. In this paper a heterogeneous hybrid vehicular wireless network consisted of IEEE 802.11b/g/e and IEEE 802.16e is being deployed inside a tunnel environment for surveillance reasons. Furthermore, we analyze the proposed vehicular wireless network architecture and provide the performance evaluation of the hybrid WiFi/WiMAX wireless network implementation during handover process after an emergency situation (fire or explosion). Moreover, we also survey through OMNeT++ simulator tool the performance of the hybrid wireless network over the handover procedure. Finally, we provide a comparison between the experimental and simulated results emphasizing on link quality metrics such as average packet end-to-end delay, SNR and throughput.

High speed frequency synthesizer based on PLL

A new frequency synthesis technique is proposed that eliminates trade-off dilemma between small settling time and good resolution, ideal for fast frequency hopping systems. The frequency synthesizer is based on a PLL that employs a digital phase accumulator that has the property to calculate the phase difference of the two different input frequencies (reference frequency and output frequency), at the maximum possible rate. This digital phase accumulator normalizes the phase increments of the two input frequencies by multiplying the phase, instead of dividing the frequency, as done in the traditional PLL based frequency synthesizer. Therefore, the sampling rate of the phase of each frequency is not reduced down to the step frequency of the synthesizer, but is as high as the reference and the output frequencies. This results in an output from the digital phase accumulator which has harmonics at high frequencies which can be cut-off by a wide bandwidth LPF. As a result, the settling time of the synthesizer is independent of the frequency step, corresponding to the resolution, and can be reduced dramatically compared to the settling time achieved by a high resolution ordinary PLL based frequency synthesizer.

Next generation millimeter wave backhaul radio: Overall system design for GbE 60GHz PtP wireless radio of high CMOS integration

In this paper we present the implementation of an experimental FDD, QPSK, millimeter-wave radio modem (57–64 GHz) for Point to Point (PtP) wireless backhaul applications. The transceiver supports GbE targeting a two-chip solution plus the antenna subsystem, aiming at highly integrated functions in 90nm CMOS technology, for a range of more than 1km. Achieving these levels of overall integration and silicon implementation requires many technological challenges and innovative design approaches. Furthermore, it allows for drastic changes of relevant cost factors enabling the wireless backhaul deployment for broadband services. The present paper is an outcome of the NexGenMiliwave project aiming to prove that it is possible to provide integrated solutions in silicon, based on demanding high frequency PtP requirements and significantly reduce the cost of the relevant backhaul network deployment.

WiMAX-WLAN Vehicle-to-Infrastructure Network Architecture during Fast Handover Process

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.