Keying

About: Keying is a research topic. Over the lifetime, 6598 publications have been published within this topic receiving 82943 citations.

An Iterative Equalization and Decoding Approach for Underwater Acoustic Communication

Abstract: In this paper, we present an iterative approach for recovering information sent over a shallow underwater acoustic (UWA) communication channel. The procedure has three main tasks: estimation of channel model parameters (CMPs), channel equalization, and decoding. These tasks are performed cyclicly until the algorithm converges. Information bits are convolutionally encoded, punctured and permuted, mapped into quaternary phase-shift keying (QPSK) symbols, linearly modulated, and transmitted through a downward-refracting ocean waveguide. Training symbols are prepended to the transmitted sequence for initial estimation of CMPs. Our algorithm processes data from a single receive sensor. Data are received on a vertical array and the performance of the algorithm for each sensor in the array is examined. There is negligible Doppler spread in the received data. However, difference between transmitter and receiver clocks as well as slight motion of the receive array produce a nonnegligible compression of the received signals. Consequently, there is observable Doppler ldquoshift.rdquo Nonuniform resampling of the data produces time series we model as the output of a linear time-invariant system. Resampling and CMP estimation are done iteratively, in conjunction with equalization and decoding. The algorithm successfully processes the data to yield few or no information bit errors.

Comparison of different DQPSK transmitters with NRZ and RZ impulse shaping

Abstract: We compare three different differential quadrature phase-shift keying (DQPSK) transmitters: One with parallel Mach-Zehnder modulators (MZM), one with a MZM and a phase modulator (PM) in series and a new one with a single PM. Although they all generate optical DQPSK signals, it turns out that their performance differs with respect to bit error probabilities, chromatic dispersion and nonlinearity tolerance for nonrectangular impulse shaping. I. I NTRODUCTION Differential quadrature phase-shift keying (DQPSK) is a quaternary phase modulation format (1) which has recently been attracting attention because of its greater spectral e ffi- ciency compared to binary formats such as intensity modu- lation (IM) or differential binary phase-shift keying (DPS K) (2). As a quaternary format, DQPSK transmits 2 bit/symbol as opposed to only 1 bit/symbol for the binary formats. Different DQPSK transmitters have been proposed (1) (3). We compare the performance of three different DQPSK transmitters (TX) at bit rate Rb = 40 Gbit/s with respect to bit error probabilites (BEP), chromatic dispersion (CD) tolerance and nonlinearity tolerance with computer simulations.

Millimeter-Wave Transmission for Small-Cell Backhaul in Dense Urban Environment: a Solution Based on MIMO-OFDM and Space-Time Shift Keying (STSK)

Abstract: Next generation wireless standards will exploit the wide bandwidth available at the millimeter-wave (mm-Wave) frequencies, in particular the $E$ -band (71–76 and 81–86 GHz). This large available bandwidth may be converted into multi-gigabit capacity, when efficient and computationally affordable transceivers are designed to cope with the constrained power budget, the clustered fading, and the high level of phase noise, which actually characterize mm-wave connections. In this paper, we propose a viable multiple-input multiple-output (MIMO) solution for high bit-rate transmission in the $E$ -band with application to small-cell backhaul based on space-time shift keying (STSK) and orthogonal frequency division multiplexing. STSK provides an efficient tradeoff between diversity and multiplexing without inter-channel interference and without the need for large antenna arrays. These features make STSK theoretically preferable over other throughput-oriented space-time coding techniques, namely, spatial multiplexing and spatial modulation, which were recently considered in the literature for mm-wave MIMO applications. In this paper, we consider the most significant channel impairments related to small-cell backhaul in dense urban environment, namely, the correlated fading with and without the presence the line-of-sight, the phase noise, the rain attenuation, and shadowing. In addition, we consider small-size MIMO systems ( $2 \times 2$ and $4 \times 4$ ), and low-cost base station equipments in the perspective of easily deployable small-cell network components. Comparative results, obtained by intensive simulations targeted at assessing link performance and coverage, have clearly shown the superior performance of STSK against counterpart techniques, although obtained at the cost of a somewhat reduced spectral efficiency.

Phase-Tunable Low-Loss, $S$ -, $C$ -, and $L$ -Band DPSK and DQPSK Demodulator

Abstract: Differential phase-shift keying (DPSK) and differential quadrature phase-shift keying (DQPSK) are touted as performers and reliable advanced modulation formats for next-generation optical transmission systems. One key device enabling such systems is the delay interferometer, converting the signal phase information into intensity modulation to be detected by the photodiodes. We developed an all-fiber delay-line interferometer for DPSK and DQPSK demodulation in the S-, C-, and L-band with low insertion loss, low-birefringence, and greater than 30 dB of extinction ratio over 100 nm and 20 dB from 1460 to 1640 nm in a single device. The device also features insensitivity to mechanical vibration, very low port imbalance (0.1 dB), and very low time delay between all outputs (0.1 ps). The device is highly reliable with a demonstrated failure-in-time rate of less than 100.

Joint Radar-Communications Co-Use Waveform Design Using Optimized Phase Perturbation

Abstract: Joint radar-communications dual function has drawn lots of attention since it can make a better use of the scarce wireless frequency resources and expensive hardware platforms. In case of joint radar-communications signal co-use, many communication sequences have poor range sidelobes and thus are not very suitable for the radar function. In this paper, we present a single carrier joint radar-communications method operating in the pulsed radar mode. Digital communication sequences are first partitioned into blocks which are then mapped to digital phase-coded sequences, like binary phase-shift keying (BPSK) and quadrature phase-shift keying (QPSK) sequences. The phases of the digital sequences are perturbed a bit such that certain degrees of freedom are available to optimize for lower range sidelobes. Insignificant phase perturbation will be deemed as phase noise by a communication receiver and then phase codes can be correctly decoded; in radar-processing channels, range compression are performed with known and optimized phase perturbation such that low-range sidelobes are obtained. An implementation scheme is presented. Numerical results with BPSK and QPSK sequences indicate that little phase perturbation can significantly drop the range sidelobe level but will insignificantly rise the bit error rate.