This paper describes a new resolution method concerning the orthogonality equations of oversampled complex modulated filter banks, and it is illustrated in the context of oversampled OFDM/QAM modulations. A first simplification is related to the introduction of an equivalent system of orthogonality equation of reduced size. Its solution is expressed using different sets of angular parameters. F...

We report a hybrid secure communication of continuous-variable quantum key distribution (CV-QKD) and quadrature amplitude modulation/quantum noise stream cipher (QAM/QNSC). In QAM/QNSC a coherent multi-level optical signal is hidden in quantum noise. We demonstrated 70 Gbit/s on-line QAM/QNSC transmission over 100 km using an FPGA-based transmission and receiver, where secure keys are delivered...

In order to reduce the quantization noise of low-resolution DAC, we study a shaping technique that can reshape white an irregular spectrum, in which data subcarrier band is almost transformed into null band. Both simulation and experiment, verify effectiveness investigated scheme 25 GHz 16-QAM/32-QAM/64-QAM DMT transmission systems. The experimental results show enhance receiver sensitivity 4-b...

This research aims to investigate how effectively digital modulation performs transfer data via hybrid fiber optic and free space (FO-FSO) channels for last-mile communication systems. Digital techniques investigated are phase-shift keying (PSK) 8-PSK, 16-PSK, quadrature amplitude (QAM) 4-QAM, 16-QAM, 64-QAM. FSO is line-of-sight technology being a solution system the challenge of cables instal...

This paper presents a comparative study of 16-QAM, 32QAM, 64-QAM, and 128-QAM 140 Mbit / s digital radio in the presence of multipath fading. Conventional T-spaced and fractional tapspaced equalizers have been considered to compensate for the ISI-induced symbols. The performance measure used is the bit error ratio (BER); thus, upper and lower bounds on BER have been developed. Based on this cal...

| In this paper, multilevel coded modulation with multistage decoding and unequal error protection is discussed. Three types of unconventional partitionings for 8-PSK and 16(64)-QAM constellations with UEP capabilities are analyzed. Based on the tight upper/approximated bounds on bit error probability, it is shown that more degrees of freedom in the construction of multilevel coding and multist...

We demonstrate experimentally the transmission of single carrier 56 Gbaud 16-QAM, 8-QAM and QPSK optically modulated signals over 320, 960 and 2,880 km, respectively, using a fully packaged InP IQ modulator and a Stokes vector direct detection (SV-DD) receiver realized using discrete optics. Results show that by optimizing the carrier-to-signal-power ratio, the total throughput-times-distance p...

OFDM is a technique used in modern broadband wireless communications systems. OFDM has been adopted for wireless standards such as IEEE 802.11a. In this paper, different Power Spectral Density (PSD) curves of OFDM signal based on WLAN with various pulse shapes are presented. OFDM waveform is analyzed in frequency domain response for different modulation techniques such as BPSK, QPSK, 16-QAM, 64...

In this paper, the Peak to mean Envelope Power (PMEPR) of the OFDM codes generated from an 16-QAM constellation is discussed. Maintaining the same level of error correction properties, these codes achieve higher information rate. A new set of 16-QAM Golay sequences having PMEPR bounded up to 3dB is defined. Many recursive structures are found to generate Super Golay sequences. The recursive alg...

In this paper, a method for differential encoding of odd-bit quadrature amplitude modulation (QAM) is presented. Differential encoding would allow QAM to be transmitted over media where coherent detection is not possible owing to phase ambiguity; it would allow such a transmission without the expense of the overhead incurred in data aided transmission. An example 32-QAM constellation is propose...