Keying

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

Blind Modulation Classification for Asynchronous OFDM Systems Over Unknown Signal Parameters and Channel Statistics

Abstract: Blind modulation classification (MC) is an integral part of designing an adaptive or intelligent transceiver for future wireless communications. However, till date, only a few works have been reported in the literature for blind MC of orthogonal frequency division multiplexing (OFDM) system over frequency-selective fading environment. In this paper, a blind MC algorithm has been proposed and implemented over National Instruments (NI) testbed setup for linearly modulated signals of OFDM system by using discrete Fourier transform (DFT) and normalized fourth-order cumulant. The proposed MC algorithm works in the presence of synchronization errors, i.e., frequency, timing, and phase offsets and without the prior information about the signal parameters and channel statistics. To nullify the effect of timing offset in the feature extraction process, a statistical average has been taken over OFDM symbols after introducing uniformly distributed random timing offsets in each of the OFDM symbols. In this work, we have classified a more extensive pool of modulation formats for OFDM signal, i.e., binary phase-shift keying (BPSK), quadrature PSK (QPSK), offset QPSK (OQPSK), minimum shift keying (MSK), and 16 quadrature amplitude modulation (16-QAM). Classification is performed in two stages. At the first stage, a normalized fourth-order cumulant is used on the DFT of the received OFDM signal to classify OQPSK, MSK, and 16-QAM modulation formats. At the second stage, first we compute the DFT of the square of the received OFDM signal and then a normalized fourth-order cumulant is used to classify BPSK and QPSK modulation formats. The success rate of the proposed MC algorithm is evaluated through analytical and Monte Carlo simulations and compared with existing methods. Finally, the work is validated by providing an experimental setup on NI hardware over an indoor propagation environment.

A WDM-OFDM-PON architecture with centralized lightwave and PolSK-modulated multicast overlay

Abstract: We propose and demonstrate a novel wavelength-division-multiplexing orthogonal-frequency-division-multiplexing passive-optical-network (WDM-OFDM-PON) architecture with centralized lightwave sources and polarization shift keying (PolSK) multicast overlay. The 10-Gb/s 16QAM-OFDM point to point (P2P) signal, 2.5-Gb/s multicast PolSK signal and 2.5-Gb/s on-off keying (OOK) upstream signal are experimentally demonstrated. After transmission over 25km standard single mode fiber (SMF), 1.5dB crosstalk between the downstream signals is eliminated by employing a low pass electrical filter at the PolSK receiver. The power penalty of the upstream OOK signal at BER of 10−9 is less than 0.1dB.

Shifted carrier-hopping prime codes for multicode keying in wavelength-time O-CDMA

Abstract: In this paper, we study the use of shifted carrier-hopping prime codes (CHPC) for multicode keying in wavelength-time optical code-division multiple-access (O-CDMA) systems. By using the code's good properties of zero autocorrelation sidelobes and cross-correlation functions of at most one, each user is assigned M=2/sup m/ shifted copies of its own code matrix to represent m data bits per symbol with minimal interference. The advantages of our scheme are that: 1) a lower baud rate O-CDMA system can now support a higher bit rate; 2) no network synchronization is required; 3) no M-fold increase in code cardinality is needed, as compared with standard M-code keying; 4) the numbers of optical encoders and decoders can be reduced from M to one per user, a major hardware cost savings; and 5) user code confidentiality is enhanced, as compared with the transmission of one code matrix for each data-bit one in conventional "on-off keying" O-CDMA schemes. Finally, our performance analysis shows that there is a tradeoff between the error probability and the choice of M.

Low complexity indoor wireless data links using chirp spread spectrum

Abstract: This dissertation proposes the use of Chirp Spread Spectrum (CSS) modulation for the transfer of high-speed (>10 megabits per second) data in the indoor wireless environment. CSS utilizes the properties of chirp signals to combat the effects of multipath fading. The major advantage CSS has over other spectrum spreading techniques is its analog-only implementation. Two main methods for deploying CSS are described: Binary Orthogonal Keying (BOK), in which chirp signals with different characteristics represent different data symbols, and Direct Modulation (DM), where data is modulated using a conventional non-coherent modulation scheme, and then has its bandwidth spread by the chirp signal. Performance equations for the Gaussian channel are derived for both systems. Several other key system design parameters are identified and explored, including chirp windowing, occupied bandwidth, and quasi-RAKE filter configuration. Computer simulations and prototype measurements show close agreement with the developed theory. Raw bit error rates less than 10−5 at 20 megabits per second are achieved, with a bandwidth of 200 MHz in non line of sight wireless channels over 10 m with less than 2 milli-Watts of transmit power. Techniques for designing SAW chirp filters with both linear and nonlinear time-frequency responses are described, and measurements of a prototype SAW device are presented. Novel methods for enhancing the throughput of a binary CSS system are presented which increase the number of bits per symbol of the modulation CSS signal. Computer simulations show that data rates of 50 megabits per second are achievable for a single channel system using this method.