Modulated Data Streams Research Articles

Performance degradation of terahertz channels in emulated rain

The ever-increasing capacity demand (up to Tbps in the foreseeable future) in wireless connectivity can supposed be satisfied by terahertz communications in the band from 100 GHz to 10 THz. This has been studied over short channel distances in laboratories using higher order modulation formats (QPSK, QAM). However, only very few reports on the THz channel performance in outdoor adverse weathers conditions are available due to the involved experimental difficulties. In this article, we report the performance of terahertz channels in emulated rain by utilizing a broadband pulse source and a 16-QAM modulated data stream. We observe that, a not precisely known of raindrop size distribution can be a major source of uncertainty for theoretical precipitation of power attenuation and bit error rate (BER). We also find that the channel degradation in rain is mainly due to power attenuation.

Coupling Data Transmission for Multiple-Access Communications

We consider a signaling format where the information to be communicated from a single or multiple transmitters to a receiver is modulated via a superposition of independent data streams. Each data stream is formed by error-correction encoding, constellation mapping, replication and permutation of symbols, and application of signature sequences. The relations between the data bits and modulation symbols transmitted over the channel can be represented by a sparse graph. In the case where the modulated data streams are transmitted with time offsets the receiver observes spatial coupling of the individual graphs into a graph chain enabling efficient demodulation/decoding. We prove that a two-stage demodulation/decoding method, in which iterative demodulation based on symbol estimation and interference cancellation is followed by parallel error-correction decoding, achieves capacity on the additive white Gaussian noise channel asymptotically. We compare the performance of the two-stage receiver to the receiver which utilizes hard-decision decoding feedback between the error-correction decoders and the iterative demodulator and estimate the gap between the achievable spectral efficiency and the channel capacity.

Frequency-division multiplexer and demultiplexer for terahertz wireless links

The development of components for terahertz wireless communications networks has become an active and growing research field. However, in most cases these components have been studied using a continuous or broadband-pulsed terahertz source, not using a modulated data stream. This limitation may mask important aspects of the performance of the device in a realistic system configuration. We report the characterization of one such device, a frequency multiplexer, using modulated data at rates up to 10 gigabits per second. We also demonstrate simultaneous error-free transmission of two signals at different carrier frequencies, with an aggregate data rate of 50 gigabits per second. We observe that the far-field spatial variation of the bit error rate is different from that of the emitted power, due to a small nonuniformity in the angular detection sensitivity. This is likely to be a common feature of any terahertz communication system in which signals propagate as diffracting beams not omnidirectional broadcasts.

Efficient Parallelization of Polyphase Arbitrary Resampling FIR Filters for High-Speed Applications

This article describes a method for increasing the sampling rate of efficient polyphase arbitrary resampling FIR filters. An FPGA proof of concept prototype of this architecture has been implemented in a Xilinx Kintex-7 FPGA which is able to convert the sampling rate of a signal from 500 MHz to 600 MHz. This article compares this new architecture with other best known efficient resampling architectures implemented on the same FPGA. The area usage on the FPGA shows that our proposed implementation is very proficient in high bandwidth applications without requiring significantly more resources on the FPGA. A theoretical calculation of the resampling error introduced on a modulated data stream is provided to evaluate the new architecture against other existing resampling architectures.

Design and Analysis of an OFDM-based Differential Chaos Shift Keying Communication System

In this paper, a new non-coherent chaos-based communication scheme, named orthogonal frequency division multiplexing based different chaos shift keying (OFDM-DCSK), is presented inspired by multi-carrier direct sequence code- division multiple access (MC-DS-CDMA) system, multi-carrier DCSK (MC-DCSK) system, and channel estimation of OFDM system. In this scheme, all of the occupied subcarriers are grouped into several groups. In each group, one chaotic reference is transmitted over the central subcarrier, while multiple modulated data streams are transmitted over the remaining subcarriers. Therefore, this transmitter structure increases the spectral efficiency, compared with the conventional DCSK system. At the receiver side, no radio frequency delay circuits are needed to demodulate the received data, which makes the system easy to implement in practice. The bit error rate (BER) performance of the OFDM-DCSK system is derived based on Gaussian approximation under additive white Gaussian noise (AWGN) channel. Simulation results are given under AWGN and two-path Rayleigh flat fading channel, which confirm the effectiveness of this new design.

Design and Analysis of a Multi-Carrier Differential Chaos Shift Keying Communication System

A new Multi-Carrier Differential Chaos Shift Keying (MC-DCSK) modulation is presented in this paper. The system endeavors to provide a good trade-off between robustness, energy efficiency and high data rate, while still being simple compared to conventional multi-carrier spread spectrum systems. This system can be seen as a parallel extension of the DCSK modulation where one chaotic reference sequence is transmitted over a predefined subcarrier frequency. Multiple modulated data streams are transmitted over the remaining subcarriers. This transmitter structure increases the spectral efficiency of the conventional DCSK system and uses less energy. The receiver design makes this system easy to implement where no radio frequency (RF) delay circuit is needed to demodulate received data. Various system design parameters are discussed throughout the paper, including the number of subcarriers, the spreading factor, and the transmitted energy. Once the design is explained, the bit error rate performance of the MC-DCSK system is computed and compared to the conventional DCSK system under an additive white Gaussian noise (AWGN) and Rayleigh channels. Simulation results confirm the advantages of this new hybrid design.

SER Performance of M-ary QAM OFDM System under AWGN Channel

is a multicarrier technique in which modulated data streams are divided into number of parallel substreams which occupies a very less bandwidth. However, full justice was done in proper utilization of bandwidth in OFDM where subcarriers overlap orthogonally. In this paper, the performance analysis of M-ary QAM-OFDM wireless communication systems affected by AWGN in terms of Symbol Error Rate is presented. The MATLAB script based model of the M-ary QAM-OFDM systems with normal AWGN channel is made for study of error performance. Lastly a comparative study of error performance of 64,128 and 256 QAM-OFDM system is made showing the effects of increase in value of M on SER.

Ultrabroadband Wireless–Optical Transmission Links Using Axial Slot Leaky Feeders and Optical Fiber for Underground Transport Topologies

This paper describes a hybrid leaky feeder/fiber-optic transmission system for use in underground transportation networks. The system has a 1.6-Gb/s throughput and features an ultrawideband axial slot leaky feeder, which is based on a standard semirigid coaxial cable as a fixed antenna. Patch antennas with a 4-GHz center frequency and a 1-GHz, -10-dB bandwidth are proposed for the rolling stock. This highest reported data rate was achieved by combining two 800-Mb/s in-phase and quadrature (I and Q) phase-shift keying (PSK) modulated data streams. A specially designed carrier and data synchronization system provided a convenient interface to a 1.3/1.5-mum diplex single-mode fiber-remoting network. The measured 2.4- to 6-GHz leaky feeder bandwidth allows multiradio multiband wireless mesh networking and, therefore, low-contention gigabit rolling stock data communications.

Digital Encoder for RF Transmit Waveform Synthesizer

We are designing an encoder for conversion of a Nyquist-rate N-bit digital word into a high frequency stream of single-bit data, to enable a novel architecture for a digital waveform synthesizer. The multi-bit to single-bit data conversion is performed by a new encoding scheme called the ldquostaggered thermometer code.rdquo Similar to the delta-sigma code, the staggered thermometer code also pushes most of the quantization noise to higher frequencies which can be easily filtered out with a low-pass filter. This encoder, built with elementary RSFQ cells, relies only on the merger of periodic pulse streams of different frequencies, and therefore, is much simpler to implement than a delta-sigma modulator which requires an accumulator and a multi-bit feedback loop. To avoid the permanent energy loss associated with low-pass filtering of high frequency components of the single-bit data stream, we also implement a novel digital circuit that acts as an amplifier by converting the pulse density modulated data stream into a pulse width modulated data stream. This digital amplifier changes the frequency spectrum by concentrating the energy in the fundamental while reducing higher harmonics. We have designed and fabricated a 4-bit and a 7-bit encoder circuit with integrated digital amplifier, and have demonstrated its operation up to a clock speed of 12.8 GHz.

Implantable 9-Channel Telemetry System for In Vivo Load Measurements With Orthopedic Implants

Knowledge of the loads to which orthopedic implants are subjected is a fundamental prerequisite for their optimal biomechanical design, long-term success, and improved rehabilitation outcomes. In vivo load measurements are more accurate than those obtained using mathematical musculoskeletal models. An inductively powered integrated circuit inside the implant measures six load components as well as the temperature and supplied voltage. This low-power circuit includes a 9-channel multiplexer, a programmable memory, a pulse interval modulator, and a radio-frequency transmitter. Together with a few passive components, the integrated circuit is mounted on a ceramic substrate with thick-film hybrid technology. The sensor signals are multiplexed, modulated, and transmitted to an external device. The microcontroller of the external device regulates the alternating magnetic field produced by a power oscillator and synchronizes the pulse interval modulated data stream. A personal computer displays forces, moments, and temperatures in real time. The new telemetry transmitter has, thus far, been used for in vivo load measurements in three patients with shoulder endoprostheses. Eight instrumented vertebral body replacements are ready for implantation, and an instrumented tibial tray is being submitted to laboratory tests.

Over 26-nm Wavelength Tunable External Cavity Laser Based on Polymer Waveguide Platforms for WDM Access Networks

We demonstrated a widely tunable hybrid-integrated external cavity laser on a polymer-based waveguide platform. The lasing wavelength was tuned over 26 nm by locally heating the surface-relief-type polymer waveguide Bragg grating fabricated by using the phase mask. The phase-control heater section was inserted between the laser diode and the Bragg grating for the fine wavelength tuning and the stable single-mode lasing. In the 100-GHz-spaced wavelength-division-multiplexing systems, the 1.25-Gb/s directly modulated data streams at each tuned 32 channel were successfully transmitted

Demultiplexing of 80-Gb/s pulse-position modulated data with an ultrafast nonlinear interferometer

Pulse-position modulation may be used to reduce patterning effects arising from gain saturation in all-optical switches employing semiconductor optical amplifiers. We present a novel technique for return-to-zero pulse-position modulation of data suitable for use in optical time-division-multiplexed (OTDM) networks. We demonstrate two methods for all-optical demultiplexing of a pulse-position modulated data stream using an ultrafast nonlinear interferometer. Error-free operation is obtained for demultiplexing from OTDM data rates as high as 80 Gb/s with control pulse energies of 25 fJ.