Sharif Digital Repository

We consider multirate time-hopping ultra-wideband (TH-UWB) communication systems where each user can have several multirate services. We investigate both constant spreading factor scheme, which uses multicode, and variable spreading factor scheme, which uses constant chip time and variable frame number. For multicode structure, we consider two methods. In the first, one kind of signature (PN) code is used to distinguish users and their diverse services alike. Whereas in the second one different users and different services of the same user are distinguished through two kinds of signature codes, namely PN code and Walsh code, respectively. For variable spreading factor scheme, one signature... 

Time domain equalizers are used in the receiver of a discrete multitone (DMT) receiver to compensate the channel effects on the received signal. There are a lot of DMT equalization algorithms presented in the literature, but recently a novel Per Tone equalizer structure was proposed which offers some advantages over the previous traditional ones. The objective of this paper is to provide an overview of the important concepts of this technique and evaluate its initialization complexity. The performance of this technique is also compared with typical time-domain equalization algorithms in different simulation environments. © 2004IEEE  

In this paper, we present an analytical model to analyze the influence of deep level traps on the static and dynamic responses of transistor laser (TL). Our analyze is based on analytically solving the continuity equation and rate equations including the effect of the deep level trap (DLT), which incorporate the virtual states as a conversion mechanism. The results of simulation show that the main characteristics of laser such as threshold current, quantum efficiency, output power, and modulation bandwidth are affected by total density of traps in the active region  

In this paper we present an analytical model to analyze the influence of deep level traps on the static and dynamic responses of transistor laser (TL). Our analysis is based on analytically solving the continuity equation and rate equations including the effect of the deep level trap (DLT), which incorporates the virtual states as a conversion mechanism. The results of simulation show that the main characteristics of laser such as threshold current, quantum efficiency, output power, and modulation bandwidth are affected by total density of traps in the active region  

In this paper, for the first time, we present a small signal circuit model of InGaAs/GaAs self-assembled quantum dot (QD) laser, based on the standard rate equations. By using the presented model, modulation response of QD laser is investigated. The simulation results show that retarded carrier relaxation due to phonon bottleneck degrades the modulation and impulse responses of a QD laser. It is shown that modulation bandwidth is increased with larger inhomogeneous broadening. Also, our model describes the effects of carrier recombinations inside and outside of a QD region, on the modulation response behavior