Baseband Data Research Articles

Ultrasound Beamforming Using Compressed Data

The rapid advancements in electronics technologies have made software-based beamformers for ultrasound array imaging feasible, thus facilitating the rapid development of high-performance and potentially low-cost systems. However, one challenge to realizing a fully software-based system is transferring data from the analog front end to the software back end at rates of up to a few gigabits per second. This study investigated the use of data compression to reduce the data transfer requirements and optimize the associated trade-off with beamforming quality. JPEG and JPEG2000 compression techniques were adopted. The acoustic data of a line phantom were acquired with a 128-channel array transducer at a center frequency of 3.5 MHz, and the acoustic data of a cyst phantom were acquired with a 64-channel array transducer at a center frequency of 3.33 MHz. The receive-channel data associated with each transmit event are separated into 8 × 8 blocks and several tiles before JPEG and JPEG2000 data compression is applied, respectively. In one scheme, the compression was applied to raw RF data, while in another only the amplitude of baseband data was compressed. The maximum compression ratio of RF data compression to produce an average error of lower than 5 dB was 15 with JPEG compression and 20 with JPEG2000 compression. The image quality is higher with baseband amplitude data compression than with RF data compression; although the maximum overall compression ratio (compared with the original RF data size), which was limited by the data size of uncompressed phase data, was lower than 12, the average error in this case was lower than 1 dB when the compression ratio was lower than 8.

An FPGA Based Architecture for Moving Target Indication (MTI) Processing Using IIR Filters

Design and implementation of an IIR filter based Moving Target Indication (MTI) processor is presented. IIR filters offer an advantage compared to FIR filters in terms of hardware resources but are prone to problems in implementation. These are variable overflows and accumulating error. This results in a need for calculation of range and error bounds for the filter variables. This paper presents a method for dealing with these issues and proposes a time shared architecture for the processor. The design is implemented on a Virtex-4SX35 device on the Xilinx Xtreme DSP kit. The processor is tested using unprocessed baseband data from a working TA-10K air traffic control radar.

Integration of Crawling Waves in an Ultrasound Imaging System. Part 1: System and Design Considerations

An ultrasound system (GE Logiq 9) was modified to produce a synthetic crawling wave using shear wave displacements generated by the radiation force of focused beams formed at the left and the right edge of the region of interest (ROI). Two types of focusing, normal and axicon, were implemented. Baseband (IQ) data was collected to determine the left and right displacements, which were then used to calculate an interference pattern. By imposing a variable delay between the two pushes, the interference pattern moves across the ROI to produce crawling waves. Also temperature and pressure measurements were made to assess the safety issues. The temperature profiles measured in a veal liver along the focal line showed the maximum temperature rise less than 0.8°C, and the pressure measurements obtained in degassed water and derated by 0.3 dB/cm/MHz demonstrate that the system can operate within FDA safety guidelines.

A Multiband Transceiver System in 45-nm CMOS for Extended Data Rate through Notchy Wireline Channels

Various forms of discontinuities such as stubs, vias, and wire bonds can result in deep amplitude notches in wireline channels. The data rate for systems operating using such channels, in the absence of a power-hungry decision-feedback equalizer (DFE), is limited by the lowest notch frequency of the channel. This brief proposes a multiband transceiver system to overcome this limitation by upconverting part of the data using an on-off keying modulation to avoid operating near the notch frequency and multiplexes it with the original baseband data. The transceiver system implemented in 45-nm low-power CMOS and shows a 10%-50% increase in data rate with a power saving of 5%-30% over a traditional broadband system employing a DFE in exemplary channels.

An RF Based Analog Linear Demodulator

Quadrature homodyne receivers have been used extensively for wireless life sign monitoring applications. In this letter, a new single mixer receiver architecture is proposed, that uses a phase tuning method to reach optimum demodulation point, and remove the dc offset associated with homodyne receivers. This method significantly simplifies the receiver architecture, and eliminates the demodulation step of processing baseband data. Experimental results obtained with this system demonstrate that physiological signals have been obtained without distortion, and with estimated heart rate accuracy of 99% for a stationary subject.

TLSync

As the number of cores on a single-chip grows, scalable barrier synchronization becomes increasingly difficult to implement. In software implementations, such as the tournament barrier, a larger number of cores results in a longer latency for each round and a larger number of rounds. Hardware barrier implementations require significant dedicated wiring, e.g., using a reduction (arrival) tree and a notification (release) tree, and multiple instances of this wiring are needed to support multiple barriers (e.g., when concurrently executing multiple parallel applications). This paper presents TLSync, a novel hardware barrier implementation that uses the high-frequency part of the spectrum in a transmission-line broadcast network, thus leaving the transmission line network free for non-modulated (baseband) data transmission. In contrast to other implementations of hardware barriers, TLSync allows multiple thread groups to each have its own barrier. This is accomplished by allocating different bands in the radio-frequency spectrum to different groups. Our circuit-level and electromagnetic models show that the worst-case latency for a TLSync barrier is 4ns to 10ns, depending on the size of the frequency band allocated to each group, and our cycle-accurate architectural simulations show that low-latency TLSync barriers provide significant performance and scalability benefits to barrier-intensive applications.

Heterogeneous radio-over-fiber passive access network architecture to mitigate Rayleigh backscattering interferometric beat noise

We propose and experimentally demonstrate a hybrid radio-over-fiber (ROF) wavelength division multiplexed and time division multiplexed passive optical network (WDM-TDM PON) architecture to mitigate Rayleigh backscattering (RB) interferometric beat noises. Here, only a single wavelength is needed at the central office (CO) to generate the downstream baseband data for optical wired application and optical millimeter-wave (mm-wave) signal for wireless application. The upstream signal is produced by remodulating the downstream signal. No optical filter is required at the optical network unit/remote antenna unit (ONU/RAU) to separate the optical wired and optical mm-wave signals. In the proposed network, 10 Gb/s differential phase shift keying (DPSK) signal is used for the downstream optical wired application and 2.5 Gb/s on-off keying (OOK) signal on 20 GHz carrier is used for the optical mm-wave signal. In each ONU, a reflective optical semiconductor amplifier (RSOA) is used to remodulate and produce a 2.5 Gb/s OOK format for upstream traffic. As the back-refection produced by the downstream DPSK signal and the upstream OOK signal is traveling in different fiber path, RB noise at the CO can be completely mitigated.

Investigation of transmission performance of single sideband radio over fiber link

We have presented a detailed investigation of the impact of group velocity dispersion (GVD) on the single sideband (SSB) radio over fiber (RoF) links. The theoretical and simulated results show that the transmission distance of the SSB RoF link is limited by the time shifting of the codes due to the GVD, and the code distortion could be suppressed if only one of optical carriers is modulated with baseband data. Moreover, the transmission performance of the SSB RoF link could be further improved by reducing the power of the optical carrier to optimize the carrier-to-sideband ratio.

Six-Port Gigabit Demodulator

This paper presents measurement results for a six-port-based demodulator designed for a center frequency of 7.5 GHz and with a bandwidth of 1 GHz for operation in the ultra-wideband band. The demodulator includes the six-port correlator, diodes, and amplifiers needed to recover the baseband data. Measurement results show that the prototype supports data rates at 1.7 Gbit/s with bit-error rate if a two-tap linear equalizer is used and bit-error rate if only threshold detection is used. The measured performance of the used six-port correlator including the amplifiers is presented and their influence on the overall system performance is discussed. Limitations in the present system and possible improvements are also considered.

Optical Generation of Modulated Millimeter Waves Based on a Gain-Switched Laser

We propose and demonstrate two configurations for optical millimeter-wave (mm-wave) generation and transmission of 3-Gb/s downstream data based on a gain-switched laser (GSL). The first configuration generates an optical comb spectrum from a GSL that can be appropriately filtered to generate two optical sidebands with 60-GHz separation. These sidebands are modulated with baseband data by using an external intensity modulator and then transmitted via optical fiber to the remote antenna unit (RAU). The second configuration produces a modulated optical frequency comb by driving the laser with both RF local oscillator and data streams coupled together and then followed by the same optical filters to generate two modulated optical sidebands. At the RAU, these two sidebands are heterodyned using a photodetector to generate the electrical modulated mm-wave signal. We investigate the distribution of these two methods over 3-km fiber with 2-m wireless link and demonstrate the system simplicity and cost efficiency for mm-wave over fiber systems. Both configurations are simulated to verify our obtained results and show system performance at higher bit rates.

A Millimeter-Wave Self-Oscillating Mixer Using a Mode-Locked Laser

This paper presents a study of millimeter-wave optoelectronic downconversion using the self-oscillating mixer concept. Baseband data are transmitted using a 40-GHz electrical carrier; however, detection only requires a much lower speed photodiode. Both homodyne and heterodyne configurations are presented with the former requiring injection locking which can limit the maximum baseband data rate.

A 3–5 GHz BPSK transmitter for IR-UWB in 0.18 μm CMOS

This paper presents a transmitter IC with BPSK modulation for an ultra-wide band system. It is based on up-conversion with a high linearity passive mixer. Unlike the traditional BPSK modulation scheme, the local oscillator (LO) is modulated by the baseband data instead of the pulse. The chip is designed and fabricated by standard 0.18 μm CMOS technology. The transmitter achieves a high data rate up to 400 Mbps. The amplitude of the pulse can be adjusted by the amplitude of the LO and the bias current of the driver amplifier. The maximum peak-to-peak amplitude of the pulse is 600 mV. It consumes only 20.3 mA current with a supply voltage of 1.8 V when transmitting a pulse at the maximum data rate. The energy efficiency is 91.4 pJ/pulse. The die area is 1.4 × 1.4 mm2.

Wireless Hybrid Mode Locked Lasers for Next Generation Radio-Over-Fiber Systems

This paper demonstrates a novel technique to wirelessly injection lock a state-of-the-art 40 GHz mode locked laser and shows baseband data transmission using such a technique. This allows mode locked lasers to be used as millimeter wave modulated data sources for next generation Radio-over-Fiber systems. Binary phase shift keying data transmission rates of up to 22 Mb/s have been demonstrated for a short wireless range of 10 cm. These devices can also be used as millimeter wave phase shifters for advanced antenna beam steering systems.

Full-duplex radio-over-fiber system based on a modified single-side band modulation

A full-duplex radio-over-fiber system based on a modified single-sideband using external modulator is proposed and demonstrated. At the central station, a CW lightwave is intensity-modulated by a RF signal to generate a DSB signal. After the central carrier and the two first-order sidebands are separated by a FBG, the central carrier is modulated with a baseband data at 2.5 Gbit/s. Then, it is recombined with the un-modulated first-order sidebands to generate optical millimeter-wave by an optical coupler with a certain coupling coefficient and transmitted to the base station over single-mode fiber. The central carrier and one of the first-order sidebands are beaten to generate the mm-wave when they are detected by an optical receiver. Another first sideband is reused as carrier for uplink connection. The dispersion performance of the generated mm-wave is theoretically analyzed; one can see that the effect of dispersion and requirement of the optical power are reduced. The PIN-PD can avoid working in a high-DC saturation range which may distort the RF components and depress the responsibility of the detector. The stimulant results show that the system can reduce the effect of dispersion effectively, and immune the fading effect and the walking-off signals. It is suitable for a long distance transmission.

Receiver I/Q Imbalance: Tone Test, Sensitivity Analysis, and the Universal Software Radio Peripheral

The problem of determining the gain imbalance, quadrature skew, and local oscillator leakage of contemporary radio frequency receivers by tone test is considered. A least squares approach for indirect estimation of the sought-for parameters is proposed, which is linear in six out of its seven parameters. The performance of the method, particularly its accuracy as a function of measurement time, imbalance parameters, and signal-to-noise ratios, is investigated. The theoretical predictions of the performance are illustrated by Monte Carlo simulations and experimental data that are obtained from testing several universal software radio peripheral (USRP) receivers. This paper shows that, for the studied off-the-shelf receivers, gain imbalance and quadrature skew may accurately be predicted (i.e., < 0.1 dB and <, respectively) by employing baseband data covering only a handful of full periods of the excitation stimuli. Using short records of data, this paper also shows that local oscillator leakage adding a bias term in the receiver baseband data may suffer from a systematic bias error on the order of 15 dB in the estimate. To obtain local oscillator leakage estimates with an uncertainty on the order of 1 dB, the measurement time has to be increased by two orders of magnitude.

10-Mbps Short-Range Baseband Wireless Communications via Quasi-Static Electric Fields

We propose a novel short-range wireless communications technology that uses quasi-static electric fields; it enables data communication between devices separated by up to 10cm via dielectric media at a speed of 10Mbps. It is considered to be a secure wireless technology since communication area is restricted to below about 10cm. To suppress electromagnetic radiation, we adopted a baseband transmission scheme in which the quasi-static electric field is directly modulated by 10BASE-T data signals. Since the spectra of the data signals are concentrated to below 20MHz, the amplitude of the electric field rapidly decreases outside the communication area. This contributes to enhancing security of the communications system. In this paper, we explain a basic principle of the short-range wireless communications technology. Since baseband data signals are carried by the quasi-static electric field, the quality of the communication is easily degraded by the existence of the earth ground. To isolate the communications system from the earth ground, we introduce a novel electro-optic sensor to receive the quasi-static electric field. With the electro-optic sensor, stable data communication is possible at 10Mbps via dielectric materials, such as a wooden table.

A Novel Ternary CDMA Code for TPSK Modulation Scheme

In code division multiple access (CDMA), two or more chips are grouped together to form symbols and each symbol is transmitted during the symbol period. The phase shift keying (PSK) modulation techniques map the digital baseband data into two or more possible signals by varying the phase of a radio frequency (RF) carrier. The recently proposed PSK scheme called ternary PSK (TPSK) scheme can convey three possible symbols. In this paper, a novel ternary based CDMA sequence so-called large area synchronous even ternary (LAS-ET) sequence is introduced to increase spectrum efficiency in TPSK scheme. Its sequence duty ratio and cross-correlation are analyzed. The performance analysis of this sequence is compared with the large area synchronous (LAS) sequence in term of symbol error rate and chip error rate (CER) over various channel models. It is shown that TPSK scheme in LAS-ET sequence outperforms LAS sequence in terms of CER evaluation. At the same time, the spectrum efficiency is doubled when a pair of chips in LAS-ET sequence is mapped into one symbol.

Optical millimeter-wave generation and transmission system for 1.25Gbit/s downstream link using a gain switched laser

In this paper, we propose a novel and cost effective system for optical millimeter-wave (mm-wave) generation and transmission of downstream data based on a gain switched laser (GSL). The GSL produces an optical comb spectrum that can be appropriately filtered to generate two optical sidebands spaced by more than 4 times the repetition rate of the GSL. These sidebands are modulated by baseband data and then transmitted via optical fiber to the remote antenna unit (RAU). At the RAU, the two sidebands are heterodyned using a photodetector to generate the electrical modulated mm-wave signal, before demodulation using self mixing. We demonstrate the distribution of 1.25 Gbit/s data OOK modulated onto a 60 GHz carrier, similar to that used in the IEEE 802.15.3c draft standard, over fiber lengths up to 62 km.

A 200-pJ/b MUX-Based RF Transmitter for Implantable Multichannel Neural Recording

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This paper presents a 400-MHz energy-efficient offset quadrature phase-shift keying (O-QPSK) transmitter for implantable multichannel neural recording applications. Transmitters for these applications must operate at low power while delivering a high data rate. The proposed transmitter incorporates a phase MUX, which directly implements the phase-shift keying operation. The O-QPSK modulation signal is generated by selecting one of the four quadrature phases based on the baseband data via the phase MUX. The power amplifier adopts the inverter-type topology for it is compatible with the quasi-constant-envelope nature of the O-QPSK signal. Implemented in a 0.18-<formula formulatype="inline"> <tex Notation="TeX">$\mu{\hbox{m}}$</tex></formula> CMOS process, the whole transmitter dissipates 2.9 mA from a 1.2-V supply. With a maximum data rate of 17.5 Mb/s, the proposed transmitter achieves an energy efficiency of 200 pJ/bit and is capable of delivering an output power up to <formula formulatype="inline"> <tex Notation="TeX">${-}{\hbox{8 dBm}}$</tex></formula>. </para>

Time domain model validation of a nonlinear block-oriented structure

A crystal detector is studied as a valid candidate reference element for the phase calibration of the large-signal network analyzer (LSNA) for modulated excitations. However, one cannot use a crystal detector straightforwardly as a phase reference element, since a crystal detector inherently introduces phase distortions. Hence, the identification and validation of a parametric black-box model of the detector is needed. In this work, a nonlinear feedback model for a crystal detector is constructed: the model contains a low-pass filter in the feedforward path and a Wiener system in the feedback loop. The model is estimated from baseband data and needs to be validated for use with high-frequency signals: the model needs to be extrapolated to RF frequencies, which is quite an arduous task. The validation of the extrapolated model is performed using two approaches: (i) the RF narrow band modulated signal is applied to the extrapolated model structure and the output signal is computed; (ii) the physical representation of the model structure is translated into its differential equation and by means of this equation, the low-frequency output envelope is computed for RF input signals. The second approach requires a slight modification of the extracted model compared to the model used in the first approach, with respect to the function describing the static nonlinear behavior. The deviation between the modeled output envelope and the measured output envelope is evaluated for both approaches. The method (ii) that computes the output of the detector in the time domain by means of solving a differential equation that characterizes the identified nonlinear feedback model gives the overall best results for predicting the magnitude and the phase of the detector output spectrum and the amplitude behavior of the time domain output waveform. The mean deviation in magnitude between the modeled and measured envelope equals 2.6 dB. This approach significantly outperforms the first method (i) as the mean deviation between the phase of the modeled and measured envelope equals 8.2°.