Emil Novakov

Optical Distribution and Upconversion of MB-OFDM in Ultrawide-Band-Over-Fiber Systems

Broadband radio-over-fiber networks are raising great interest for intrabuilding distribution and signal processing of ultrawide-band (UWB) signals. In this paper, a unique optical system based on an external modulator biased either in linear or nonlinear regime has been used to realize both distribution of multiband orthogonal frequency-division multiplexing (MB-OFDM) UWB signal and all-optical frequency upconversion of UWB-OFDM subband. The impact of the nonlinearity of the optical link on the MB-OFDM signal is investigated through a simulation model of the complete UWB-over-fiber system. Results have shown enhanced performance of upconverted MB-OFDM subband compared to direct transmission due to optical noise reduction. First experimental results have confirmed simulation results.

An optical power efficient asymmetrically companded DCO-OFDM for IM/DD systems

Unipolar forms of orthogonal frequency division multiplexing (OFDM) such as DC biased optical OFDM (DCO-OFDM) and asymmetrically clipped optical OFDM (ACO-OFDM) are widely used in intensity-modulated and direct detection (IM/DD) systems. At low data rate, ACO-OFDM is more efficient in terms of optical power but it suffers from spectral inefficiency. For large constellations, DCO-OFDM with large DC bias has more optical power efficiency, since it requires lower constellation size than ACO-OFDM. However, the required DC bias to obtain an acceptable clipping noise degrades the optical power efficiency. To overcome these drawbacks, we propose an optimized DCO-OFDM technique capable to transmit large constellations with a moderate DC bias. To reduce the clipping impact, a linear companding function is used in order to compress the negative part of the bipolar signal and therefore to reduce the amount of the clipped peaks and the loss of information. We demonstrate that the proposed technique has better bit error rate and optical power performances than conventional DCO-OFDM and ACO-OFDM. For a bit rate/normalized bandwidth of 6, a gain of 4dB in optical power is reached.

An Ultra-Wideband Impulse-Radio Communication Method and Transceiver

The present paper describes the physical layer of an Ultra-Wideband Impulse Radio (UWB-IR) communication system, together with its implementation in a fully integrated transceiver. The objective of this work was to design and test a low-power radio communication system for medium data-rate, short-range communication. The system is based on Frequency Hopping On-Off Keying modulation (FH-OOK) for transmission, combined with a non-coherent demodulation scheme in the receiver. A fast-phase synchronization method for the receiver was also developed. A single chip transmitter/receiver integrated circuit (IC), incorporating the radio frequency system and the base-band signal processing chain, was produced using a 0.13 µm CMOS process. Test results showed the maximum data rate for the radio interface to be 20 Mb/s, and a reliable link was obtained at a distance of 5 m, without recourse to error-correction convolutional codes. Maximum power consumption was less than 20 mW. The simple hardware architecture, low power consumption and high achievable data rate make this system suitable for small, portable battery-powered devices.

Impact of VCSEL nonlinearity on Discrete MultiTone modulation: Quasi-static approach

Vertical-Cavity Surface-Emitting Lasers (VCSELs) represent many advantages for high data rate and low cost communication systems. However, they have a nonlinear transfer function, which could drastically affect the multicarrier modulations performances. The static characteristic is usually used to estimate the VCSEL nonlinearity impact on the Discrete MultiTone (DMT) modulation performances. In this paper, we demonstrate that the use of the static characteristic to model the VCSEL nonlinearity, overestimates the nonlinearity distortions when a large dynamic signal is modulating the VCSEL. In order to correctly estimate the VCSEL impact on the DMT modulation performances, we use the quasi-static characteristic to model the VCSEL nonlinearity. We show that the proposed modeling provides accurate estimations of the nonlinear distortions. The error vector magnitude (EVM) simulation results are very close to the measured EVM.

A low complexity, medium data rate, ultra-wideband communication method and system

This paper describes a low complexity, medium data rate, short-range, ultra-wideband (UWB) communication system suitable for low-cost and low-power personal area wireless network (PAN) applications. The system combines pulsed and orthogonal frequency communication techniques. The data bits to be transmitted are encoded with antipodal base-band signals generated using a set of orthogonal sinusoidal sub-carriers. The resulting signal is amplitude modulated into a radio-frequency signal with a bandwidth greater than 500MHz. This approach maximizes transmitted signal power for a fixed maximum power spectral density (PSD) and bandwidth. Using an antipodal modulation scheme minimizes the bit error rate of the communication system. The system can use the UWB frequency band plan defined for the multi-band orthogonal frequency division multiplexing standard (MB-OFDM), and adapt the transmitted signal spectrum to the bands authorized in a given geographical area. Experimental tests were carried out for a carrier frequency of 3.96 GHz and a bandwidth of 500 MHz (at - 10dB level), and with a maximum transmitted PSD limited to - 41.3 dBm/MHz. The proposed system has a demonstrated operational line-of-sight communication distance of 7 m for a data rate in the range 16 - 25 Mbit/s and a bit error rate less than 10-4 without an error correction code.

A direct RF signal sampling integrated receiver for IoT applications

A low power Software-Defined radio receiver operating between 400 MHz and 1.5 GHz is presented in this paper. The receiver is based on differential switched 4-path passive mixer architecture. The sampling frequency fixes the carrier frequency of the received signal and a simple RC time constant determines the receiver bandwidth. The mixer structure permits to implement flexible high-Q band-pass filters at the RF side. This receiver has improved linearity and is robust to strong out-of-band blockers and adjacent channel interferences. A wide-band 15 dB gain LNA permits to achieve a noise figure less than 4 dB between 400 MHz and 1.5 GHz. The measured sensitivity is -83 dBm with an overall gain of 55 dB over the chain. The IIP3 of the receiver is -22.7 dBm and the power consumption is 45.7 mW under a 1.2V power supply voltage. The IC receiver has been designed in a 130nm CMOS process. The receiver is suitable for Internet of Things (IoT) applications.

A low-power, direct RF signal sampling receiver for short range wireless devices

A low-power sampling receiver dedicated to Industrial, Scientific and Medical (ISM) frequency bands applications is described in this paper. The receiver is based on a 4 path passive mixer. The mixer sampling rate fixes the carrier frequency of the received signal. A simple RC low-pass filter at the mixers output determines the receiver bandwidth. The structure used allows implementing flexible high-Q band-pass filters at the radio frequency side. The receiver has improved linearity and is robust to strong out-of-band blockers and adjacent channel interferences. A wideband 15 dB gain LNA permits to achieve a noise figure less than 4 dB between 400 MHz and 1.5 GHz. An integrated circuit was designed in a 0.13μm CMOS process. The receiver was tested. The power consumption is less than 11 mW at 1.2V power supply. The RF sensitivity is -102 dBm.

A 130nm low power Software-Defined radio receiver

A low power Software-Defined radio receiver operating between 400MHz and 1.5GHz is presented, with the property to be robust to out-of-band blockers, thanks to the 4-path passive mixer architecture which acts as a high-Q bandpass filter for RF signals. The filter formed by the mixer at baseband fixes the receiver bandwidth at 10MHz. A common-gate cross-coupled LNA realizes a wideband input matching. The receiver works under 1.2V while consuming less than 10mW. The analog part consumes 4.8mW and the digital part consumes less than 5mW. The receiver has been implemented on a chip and occupies only 0.7mm2 silicon area.

Ultra-wideband communication system with transmitting pulses shaped by orthogonal frequencies signals

An ultra-wideband (UWB) short range communication system is investigated in this paper. The system is based on an on-off-keying (OOK) modulation where the transmitted data pulse is obtained by using a set of orthogonal frequency (OF) signals. This optimizes the transmitted signal power and maximizes the equivalent signal-to-noise ratio (SNR) at the receiver. The receiver uses a non-coherent energy detector. The system was tested in real communication environment. The radio frequency (RF) band from 3.7 to 4.3 GHz was used. In line-of-sight (LOS) mode and at a distance of 5 m a data rate of 20 Mbit/s was achieved without forward error correction code. The motivation of this work is to provide a non-expensive, medium data rates, and low-power short-range radio communication system suitable for personal area network (PAN) applications.

A low complexity Ultra-Wideband, Orthogonal Frequency Division Multiplexing communication system

The present paper describes an Ultra-Wideband (UWB) communication system based on the Orthogonal Frequency Division Multiplexing (OFDM) modulation scheme. The system uses a small number of sub-carrier frequencies which allow the straightforward implementation of the OFDM modulator and demodulator without the use of Discrete Fourier Transform (DFT). An experimental RF transceiver based upon the proposed method was tested. An RF band ranging from 4.2–4.8 GHz was used. The transceiver has a demonstrated operational line-of-sight communication range of 3 m for a data rate of up to 40 Mbit/s. This system is well adapted for implementation in a low-complexity and low-power integrated circuit.