Search results for "QAM"

Reducing the peak and average power for OFDM systems using QAM by constellation shaping

2009

In this paper, we present a shell mapping scheme to reduce the peak and average power of orthogonal frequency division multiplexing (OFDM) signals using quadrature amplitude modulation (QAM) by constellation shaping. Our approach can be considered as an extension of the shell mapping technique introduced originally in the V.34 recommendation of ITU-T. The shell mapping method uses multiple cost functions, each having the OFDM block length N as a parameter. The cost functions are presented in closed form for any N. The main advantage of the proposed scheme is that the peak and average power can be reduced without sacrificing the data rate, and no side information is needed at the receive sid…

MUSIC-based modal channel estimation for wideband OFDM-OQAM

2008

Orthogonal frequency division multiplexing based on offset quadrature amplitude modulation (OFDM-OQAM) over wideband frequency selective multipath channels suffers from inter-symbol interference (ISI) and inter-carrier interference (ICI) that degrade its performance. Channel estimation and equalization are needed to combat these interferences. In this paper a novel channel estimator for passband OFDM-OQAM signaling over wideband multipath channels, which is based on multiple signal classification (MUSIC) with the Spatial Smoothing technique is presented. Numerical simulation results are presented in the low number of subcarriers, i.e. wideband, scenario.

'Between two worlds' : comparisons and explorations in oriental and western music cultures

2008

Lymph node metastasis in lower lip squamous cell carcinoma in relation to tumour size, histologic variables and p27Kip1 protein expression.

2003

We studied a consecutive series of 95 patients undergoing radical surgical resection of lower lip squamous cell carcinoma (LLSCC) to assess the correlation between lymph node status and several prognostic variables, such as sex and age, tumour size, histologic grading, maximal microscopic tumour thickness, perineural infiltration and p27Kip1 protein status, to see which of these might be predictive of the development of lymph node metastases. Statistical analysis demonstrated a significant association between node status and tumour size, histological grading, maximal thickness, perineural invasion and p27Kip1 protein expression; additionally to node metastasis, low p27Kip1 protein expressio…

Combining super-orthogonal space-frequency trellis coding, constellation shaping by shell mapping, and OFDM for high data rate broadband mobile commu…

2014

In this paper, we seamlessly combine three transmission techniques to design an improved performance broadband mobile communication system with two transmit antennas. In so doing, we took inspiration from the V.34 data modem toolbox designed for public switched telephone network. We modified the constellation shaping by shell mapping algorithm to apply it only to the orthogonal frequency division multiplexing (OFDM) frame sent by the first antenna, in such a way that the peak-to-average power ratio (PAPR) is also reduced for the second antenna. We use a 24-point quadrature amplitude modulation (QAM) signal constellation on each subcarrier, while the reference system employs 16 QAM for the s…

Les représentations du paysage et de la nature dans les maqamat/munazarat yéménites d'époque prémoderne

2023

Trattato di letteratura araba yemenita del XIV-XIX secolo sul genere delle Maqamat e delle tenzoni (Munazarat)

Parameter optimization for amplify-and-forward relaying systems with pilot symbol assisted modulation scheme

2009

Article published in the journal:Wireless Sensor Network Also available from publisher: http://dx.doi.org/10.4236/wsn.2009.11003 Cooperative diversity is a promising technology for future wireless networks. In this paper, we consider a cooperative communication system operating in an amplify-and-forward (AF) mode with a pilot symbol assisted modulation (PSAM) scheme. It is assumed that a linear minimum mean square estimator (LMMSE) is used for the channel estimation at the receiver. A simple and easy-to-evaluate asymptotical upper bound (AUB) of the symbol-error-rate (SER) is derived for uncoded AF cooperative communication systems with quadrature amplitude modulation (QAM) constellations. …

Multipactor RF Breakdown in Coaxial Transmission Lines With Digitally Modulated Signals

2016

The aim of this paper is the study of the RF multipactor breakdown in coaxial transmission lines excited by a single carrier with a digitally modulated signal. Employing an in-house developed code, numerical simulations are performed to determine the RF multipactor voltage threshold for several digitally modulated signals under different modulations schemes: quadrature phase-shift keying, 16-quadrature amplitude modulation, 16-amplitude and phase-shift keying, and 32-amplitude and phase-shift keying. Moreover, a coarse method based on the envelope integration to determine the RF multipactor voltage threshold when involving arbitrary digital modulations is also presented. These results are a…

Performance Analysis of Cooperative Communication Systems with Imperfect Channel Estimation

2009

This paper investigates the effects of channel estimation errors on the symbol-error-rate (SER) performance of a cooperative communication system operating in an amplify-and- forward (AF) mode. A pilot symbol assisted modulation scheme with linear minimum mean square estimation (LMMSE) is used for the channel estimation. An accurate and easy-to-evaluate SER expression is presented for uncoded cooperative communication systems with quadrature amplitude modulation (QAM) and phase-shift keying (PSK) constellations. Numerical simulations are conducted to verify the correctness of the proposed analytical formulation. It is shown that the performance loss caused by channel estimation errors incre…

Homoérotisme dans la prose arabe d’époque mamelouke. Analyse du récit fictionnel du chapitre sur l’éphèbe dans le Nasīm al-ṣabā (La brise du vent d’e…

2022

In his work entitled Nasim al-saba (The Breeze of the East Wind), Ibn Habib al-Halabi (d. 1377) dedicates a chapter to the description of a young man (ghulam). The interest of the author in the homoerotic theme confirms the prominent place this topic occupies in premodern Arabic literature. This chapter is characterized by the presence of two parts which differ from a stylistic point of view. The incipit and the closing part present a fictional story which looks like a maqama, while the central part is entirely descriptive. From the analysis of the fictional story, this study aims to show the central role that nature occupies in this part and which seems to constitute the main subject throu…