Continuous-wave Carrier Research Articles

Smart Self-Coherent Optical Communication for Short Distances

We proposed and investigated a high-performance, energy-efficient, and low-cost self-homodyne coherent detection transmission (SHCDT) system for the 5G access network segment assuring high capacity and light digital signal processing (DSP) at the same time, avoiding the local oscillator for detection. The system implementation is based on a code-based spectral shaping at the transmitter and carrier extractor at the receiver. In the self-homodyne coherent system, a continuous wave carrier is transmitted together with the modulated signal. After transmission, at the receiver, the carrier is extracted and used as a local oscillator (LO) to prevent frequency offset with respect to the transmitted signal and phase noise, resulting in a decrease in the digital signal processing (DSP) complexity. Transmission results indicate that even a low portion of the residual local oscillator (LO) on the transmitted signal at the receiver side can lead to an increase in the signal-to-noise ratio (OSNR) penalty. Consequently, applying a proper technique to separate the unmodulated carrier and the modulated signal is the key to the system’s performance. We evaluated the self-homodyne coherent system performance through numerical analysis and experimental validation. The performance of the proposed self-coherent system, using a narrow bandwidth Fabry–Perot filter for optical carrier extraction, is evaluated experimentally on a 28 Gbaud dual-polarization 16QAM transmission system considering different code block lengths for signal spectral shaping through bit-error-rate (BER) measurements.

A 0.3-to-1-GHz IoT Transmitter Employing Pseudo-Randomized Phase Switching Modulator and Single-Supply Class-G Harmonic Rejection PA

A wideband Internet of Things (IoT) transmitter (TX) employing open-loop binary frequency-shift keying (BFSK) modulator with a pseudo-randomized phase transition (PRPT) time and a single-supply Class-G harmonic rejection (HR) power amplifier (PA) is presented. The proposed open-loop phase switching modulator eliminates the data-rate limitation in a conventional phase-locked loop (PLL)-based closed-loop modulator, while the PRPT scheme increases the effective phase resolution with a better power efficiency than delta–sigma modulation (DSM)-based randomization. Thus, a low spur level below −40 dBc is achieved with only a 4-bit phase resolution. The Class-G HR PA, including a four-level supply voltage waveform generator, is proposed as a high-efficiency and low spurious PA architecture. The proposed HR PA presents the third- and fifth-harmonics cancellation over the 0.3-to-1-GHz band, while only a single supply is required for Class-G implementation of the HR PA. The proposed BFSK TX is implemented in a 55-nm CMOS process. Measured with a 0.3-to-1-GHz continuous-wave carrier, TX output power and PA drain efficiency are 2.7 ± 0.2 dB and 52% ± 3%, respectively, operating from a 0.9-V supply. The HRs of −31.4/−42.7 and −28.2/−42.4 dBc at the third/fifth harmonics are measured at the lowest (0.3 GHz) and the highest (1 GHz) carrier frequencies, respectively. With a data rate of 1 Mb/s, the measured FSK errors are 3.6% and 4.2% at both ends of the operating frequency.

An Extended Kalman Filter for Direct, Real-Time, Phase-Based High Precision Indoor Localization

Radio-based indoor localization is currently a very vibrant scientific research field with many potential use cases. It offers high value for customers, for example, in the fields of robotics, logistics, and automation, or in context-aware IT services. Especially for autonomous systems, dynamic human–machine interaction, or augmented reality applications, precise localization coupled with a high update rate is a key. In this paper, we present a completely novel localization concept whereby received radio signal phase values that are fed into an extended Kalman filter (EKF) without any preprocessing are evaluated. Standard preprocessing steps, such as angle-of-arrival estimation, beamforming, and time-of-flight or time-difference-of-arrival estimations are not required with this approach. The innovative localization concept benefits from the high sensitivity of radio signals’ phase to distance changes and the fast and straightforward recursive computation offered by the EKF. It completely forgoes the computational burden of other phase-based high-precision localization techniques, such as synthetic aperture methods. To verify the proposed method, we use an exemplary setup employing a 24 GHz frequency-modulated continuous-wave (CW) single-input multiple-output secondary radar with 250 MHz bandwidth. A high-precision six-axis robotic arm serves as a 3D positioning reference. The test setup emulates a realistic industrial indoor environment with significant multipath reflections. Despite the challenging conditions and the rather low bandwidth, the results show an outstanding localization 3D RMSE of around 1.7 cm. The proposed method can easily be applied to nearly any type of radio signal with CW carrier and is an attractive alternative to common multilateration and multiangulation localization approaches. We think it is a quantum leap in wireless locating, as it has the potential for precise, simple, and low-cost wireless localization even with standard narrowband communication signals.

MIMO-OFDM Radar Using a Linear Frequency Modulated Carrier to Reduce Sampling Requirements

The requirement of fast analog-to-digital (AD) and digital-to-analog (DA) converters is a challenge for high-resolution orthogonal frequency division multiplexing (OFDM) radars. This paper introduces a method to increase the modulation bandwidth of an OFDM signal by using an additional frequency modulated continuous wave carrier to reduce the requirements for the AD/DA converters while maintaining a high unambiguous velocity range. Multiplexing of transmit antennas with OFDM is still possible with the combined modulation. The presented approach is verified by simulations and measurements. A reduction of AD/DA converter bandwidth by factor eight is achieved.

BLE-Backscatter: Ultralow-Power IoT Nodes Compatible With Bluetooth 4.0 Low Energy (BLE) Smartphones and Tablets

Backscatter communication promises significant power and complexity advantages for Internet of Things devices such as radio frequency identification (RFID) tags and wireless sensor nodes. One perceived disadvantage of backscatter communication has been the requirement for specialized hardware such as RFID readers to receive backscatter signals. In this paper, we show how backscatter signals can be designed for compatibility with the Bluetooth 4.0 low energy (BLE) chipsets already present in billions of smart phones and tablets. We present a prototype microcontroller-based “BLE-Backscatter” tag that produces bandpass frequency-shift keying modulation at 1 Mb/s, enabling compatibility with conventional BLE advertising channels. Using a +23-dBm equivalent isotropically radiated power continuous wave (CW) carrier source, we demonstrate a range of up to 13 m between the tag and an unmodified Apple iPad Mini as well as a PC with the Nordic Semiconductor nRF51822 chipset. With the tag 1 m from the receiver, we demonstrate a range of up to 30 m between the CW carrier source and the tag. In both cases, the existing Bluetooth stack was used, with no modifications whatsoever to hardware, firmware, or software. The backscatter tag consumes only 1.56 nJ/b, over $6\times $ less than the lowest power commercial Bluetooth transmitters.

Using single side-band modulation for colorless OFDM-WDM access network to alleviate Rayleigh backscattering effects.

In this investigation, we demonstrate a new colorless orthogonal-frequency-division-multiplexing (OFDM) wavelength-division-multiplexing passive optical network (WDM-PON) system with Rayleigh backscattering (RB) noise mitigation. Here, only a single laser source at the central office (CO) is needed to produce the downstream signal and distributed continuous-wave (CW) carrier, which will then be modulated at the optical networking unit (ONU) to produce the upstream signal. Single side-band (SSB) modulation is used to wavelength-shift the distributed CW carrier, which will be launched into a reflective semiconductor optical amplifier (RSOA) based ONU for directly modulation of 5.15 Gbps OFDM upstream signal. To avoid the radio-frequency (RF) power fading and chromatic fiber dispersion, the four-band OFDM modulation is proposed to generate a 40 Gbps downstream when a Mach-Zehnder modulator (MZM) with -0.7 chirp parameter is used. Hence, the RB circumvention can be centralized in the CO. Moreover, the signal performances of downstream and upstream are also studied and discussed in this measurement.

A passive wireless ultrasound pitch–catch system

This paper exploits amplitude modulation and demodulation to achieve a passive wireless ultrasound pitch–catch system consisting of a wireless interrogator and a combination of a wireless actuator and a sensor mounted on a structure. The wireless interrogator operates in two modes, i.e. the generation and sensing modes. At the generation mode, the interrogator transmits two microwave signals; one is amplitude modulated with the ultrasound excitation signal while the other is a continuous-wave carrier signal. Once received by the wireless actuator, the amplitude modulated signal is demodulated using the carrier signal to recover the ultrasound excitation signal, which is then supplied to a piezoelectric wafer actuator for ultrasound generation. Subsequently, the interrogator is switched to the sensing mode by transmitting a carrier signal with a different frequency. Once received by the wireless sensor, this carrier signal is modulated with the ultrasound sensing signal acquired by the piezoelectric wafer sensor to produce an amplitude modulated microwave signal, which can then be wirelessly transmitted and demodulated by the interrogator to recover the original ultrasound sensing signal. The principle and implementation of the wireless ultrasound pitch–catch system as well as the data processing of the wirelessly received sensing signal are described. Experiment results validating wireless ultrasound generation and sensing from a distance of 0.5 m are presented.

An Alternative Method for PM Signal Generation and Detection

ABSTRACTThis paper presents a novel scheme for generating a phase modulated (PM) continuous wave carrier of constant envelope and the corresponding demodulation scheme. The modulator is based on the principle of the quadrature carrier multiplexing (QCM) wherein the sine wave carrier is multiplied by the message signal, m(t), and the cosine wave carrier is multiplied by the modified signal, √ (1–m2(t)), with the constraint that │m(t)│<1. The demodulator includes an amplitude limiter, a bandpass filter, and a coherent detector. The proposed scheme introduces a maximum linear phase shift of about ±20° when the message signal amplitude is 0.9 V. The phase shift introduced into the carrier is linear to the tune of ±360° as the message signal amplitude is reduced. The proposed scheme allows for the use of high-frequency stable quadrature oscillators in the modulator and offers better noise immunity like the conventional PM carrier. Furthermore, this paper presents a view point that the existing analogue modulation schemes can be viewed as special cases of the QCM principle.

Transmission of 60 GHz Ultra Wideband Radio over Optical Fiber Using MB-OFDM

Ultra wideband radio over optical fiber (UROOF) technique enables the transmission of ultra wideband (UWB) radio signals over optical fibers by superimposing the UWB radio frequency signals of several gigahertz's on the optical continuous-wave carrier. UWB signals are characterized by an extremely large bandwidth. UWB frequency bands belong to 3.1-10.6 GHz according to the spectral mask defined by the Federal Communications Commission. This paper examines how by using multi-band orthogonal frequency division multiplexing (MB-OFDM) technique UWB transmission can be extended up to 60 GHz. MB-OFDM divides the spectrum into six band groups and 14 non-overlapping sub bands of 528 MHz bandwidth each. Each OFDM symbol is composed of 128 orthogonal subcarriers spaced 4.125 MHz apart.

Extended-reach access network with downstream radio-over-fiber (ROF) signal and upstream NRZ signal using orthogonal-WDM

We propose and demonstrate an extended-reach radio-over-fiber (ROF) access network. The double-sideband carrier-suppressed (DSCS) optical signal carries the downstream ROF signal. A continuous wave (CW) optical carrier is embedded into the DSCS optical signal and transmitted to the colorless optical networking unit (ONU)/remote antenna unit (RAU) for the upstream signal generation. At the ONU/RAU, the upstream data is orthogonally wavelength division multiplexed (WDM) onto this CW carrier; hence mitigating the cross-talk generated by the downstream signal. Analyses about the optimum power difference between the downstream and the CW signals; as well as the split-ratio are also preformed.

Photonic RF Phase Shifter Based on a Vector-Sum Technique Using Stimulated Brillouin Scattering in Dispersion Shifted Fiber

A photonic RF phase shifter is proposed and demonstrated based on a vector-sum technique using stimulated Brillouin scattering (SBS) in dispersion shifted fiber (DSF). Two optical sidebands are generated and introduced to the Brillouin processing module when an RF signal is modulated on a continuous-wave carrier by an electrooptic phase modulator. SBS amplification/depletion, as well as nonlinear SBS phase, is induced to the selective optical sideband due to the interaction between the optical sidebands and the pump wave in the DSF, thus resulting in the phase-to-intensity modulation conversion. The Brillouin erbium-doped fiber laser is implemented to generate the pump wave to fix the frequency difference between pump wave and optical sideband, which can make the phase shifter broadband. By a vector-sum technique, the phase-shifted RF signal is obtained after heterodyne mixing at the photodetector and the magnitude of the phase shift is determined by the amplitude ratio and nonlinear phase from SBS.

Rayleigh Backscattering Mitigation Using Wavelength Splitting for Heterogeneous Optical Wired and Wireless Access

We propose and demonstrate a heterogeneous optical access network using wavelength-splitting at remote-node to mitigate the Rayleigh backscattering (RB) noises. Two continuous-wave carriers are generated from each laser for wired and wireless applications, respectively. Results show that the scheme can effectively mitigate RB noises.

Seamless generation and provisioning of broadcasting and independent services in WDMPON access networks

A novel broadcasting scheme for WDM-PON based fiber access networks is proposed in this paper and downstream system experiments has been demonstrated. The broadcasting data is generated via subcarrier modulation technique. By using a delayed interferometer, the un-modulated continuous-wave carrier is separated and acts as the seeder for FP-LD injection locking and direct modulation, which is compatible with current WDM-PON infrastructures. In experiments, 2.5 Gb/s broadcasting data and 2.5 Gb/s point-to-point data are successfully integrated and transmitted in a typical WDM-PON structure with good performance.

Experimental demonstration of tolerance to FWM crosstalk in wavelength-swept WDM access systems

We confirm the tolerance of our proposed wavelength-swept wavelength division multiplexing (WDM) access system to four-wave mixing (FWM) crosstalk induced during fiber transmission. Since wavelength-swept light is employed as the carrier in the proposed system, there is little mutual interaction between different channel signals. Therefore, the tolerance to FWM crosstalk of the proposed technique is superior to that of conventional methods based on continuous-wave carriers. As a proof-of-concept, we perform experimental 10- and 20-km single-mode fiber transmissions of four-channel 1.25Gb/s/ch WDM signals with a 12.5GHz spacing, and show that FWM crosstalk has no serious impact even with a high optical power of +19dBm.

Reflectenna: a quasi passive on–off keyed microwave telemetry system for remote sensor applications

A method to transmit one-directional wireless data with low power consumption has been investigated. This system, called the ‘reflectenna’, works on the principle of transmitting information by modulating an incident continuous wave carrier signal prior to re-transmission and consists of two orthogonally linear polarised, micromachined microstrip patch antennas and a single-pole-single-throw switch that modulates the carrier signal. This quasi-passive method to transmit data has been tested with a transceiver system that transmits a 10 GHz carrier signal and demodulates the received signal reflected back from the reflectenna. The carrier signal was modulated with a 2 kHz square wave and a link with a range up to 25 m was achieved.

On the Miller–Chang Lower Bound for NDA Carrier Phase Estimation

In this letter, we derive a new Miller-Chang lower bound (MCB) for the variance of unbiased non-data-aided (NDA) carrier phase estimates obtained from a block of N samples of a linearly modulated pulse-amplitude modulation or quadrature-amplitude modulation information signal, transmitted through an additive white Gaussian noise channel. This bound is tighter than the corresponding Crame/spl acute/r-Rao lower bound (CRB) for data-aided or continuous-wave carrier phase estimation (CW-CRB), particularly when N is small. For some given N and sufficiently high signal-to-noise ratios, the MCB is tighter than the corresponding true NDA CRB. The main limitation of this new MCB is that its application is restricted to carrier phase estimators which are unbiased for all possible values of the received symbol sequence.

Signal-to-noise ratio improvement by sideband intermixing: Application to Doppler ultrasound vibrometry

A simple technique for improving the sensitivity of measuring devices based on angle modulation of a continuous-wave carrier is presented. The proposed approach involves the addition of a second carrier signal separated by twice the modulation frequency. In the Fourier domain, the upper sideband of the first carrier and the lower sideband of the second carrier intermix. By sweeping the relative phase between the two carriers, the magnitude of the resultant sideband can grow up to double the original value. In noisy environments, this effect can lead to an improvement of the signal-to-noise ratio. As a proof of concept, the technique is applied to a Doppler ultrasonic vibration sensor, with encouraging results.

Three-wavelength-division-multiplexed multichannel subcarrier-multiplexing transmission over multimode fiber with potential capacity of 12 Gb/s

We investigate the feasibility of 10-Gb/s delivery over multimode-fiber (MMF) local area networks by using the externally modulated multiple-wavelength-division-multiplexed subcarrier-multiplexed technique. In a system experiment, three externally modulated distributed-feedback lasers with different wavelengths (1551.1, 1553.6, and 1556.1 nm) are used to carry a total of 300 random-phased continuous-wave carriers for simulating 300 channels of 256-QAM signals. The transport of a potential capacity of 12 Gb/s (=40 Mb/s/spl times/300 channels) over a 4-km MMF link is demonstrated and analyzed.

High-fidelity lightwave transmission of multiple AM-VSB NTSC signals

The progress towards developing AM lightwave links for the transmission of multiple TV signals is reported. While the signal-quality objectives and transmission distances are appropriate for CATV trunking, the technology is expected to have applicability to the distribution of video signals in the subscriber loop. Highly linear 1.3- mu m distributed feedback (DFB) lasers designed expressly for analog requirements are used to transmit 42 continuous wave carriers according to the standard US CATV frequency plan. For the best lasers, when evaluated over 12 km of fiber, carrier to noise was >52 dB, composite second-order distortion was >70 dBc, and composite triple beat was >70 dBc. The relationship between measurements with continuous wave carriers and actual video signals is discussed. System design rules are offered. Properties that lead to superior analog performance are discussed. Data from 700 links indicate that composite third-order distortion generally scales with product count but that composite second-order distortion has a significant frequency-dependent component.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>