Sharif Digital Repository

In this paper we study the performance of spectrally-encoded spread-time (SE/ST) technique when applied to ultrawideband (UWB) signals in the context of wireless code-division multiple-access (CDMA) communication. In this technique UWB pulses are spectrally encoded with pseudorandom codes that are assigned uniquely to each user. We shall show that the SE/ST ultrawideband system provides an appropriate multi-user capacity in realistic UWB channels, along with the ability of narrowband interference (NBI) suppression. To this end, after obtaining a suitable statistical model for spectrally encoded spread-time signals, we investigate the performance of the system in the presence of... 

Time reversal is a technique in which a signal is pre-filtered such that it focuses both in time and space. Spatial focusing reduces interference to other co-existing systems and temporal focusing concentrates the received power in a very short interval. Energy detector is a practical receiver for ultra-wideband (UWB) time reversed signals due to its low-complexity and low-cost implementation. However, selection of an optimum integration interval to minimize the bit error rate is a major problem. Weighted energy detection is an effective technique to overcome this problem and enhance the performance of energy detectors. However, this improvement is achieved at the expense of non-trivial... 

In this brief, a generalized expression for the popular ultra wideband waveforms is derived. It is shown that all three waveforms used in ultra wideband (Gaussian, modified Hermite, and prolate spheroidal waveforms) fulfill the Sturm–Liouville differential equation. By using this unified structure, characteristics of the waveforms such as orthogonality, finite duration in time and frequency spectrum are explained. © 2008 IEEE  

A single-user receiver structure for space-time coded CDMA downlink is studied in a multiuser frequency selective channel. The proposed scheme is a two dimensional Decision Feedback Equalizer (2D-DFE), whose filters are optimized based on the MMSE criterion to cancel noise, ISI, and MUI with a reasonable complexity. By modeling the spreading codes of the interfering users as random sequences, system performance has been evaluated using the Gaussian approximation. Two models for the desired user's spreading sequence have been considered and compared. Our numerical results show that in both cases the 2D-DFE exhibits significant performance improvement and capacity enhancement over the standard... 

In this paper, two single-antenna receiver structures for multiuser space-time coded wideband CDMA downlink are studied in frequency selective fading channels. The first structure is the standard space-time coded RAKE receiver, while in the second structure, we have proposed a two dimensional Decision Feedback Equalizer (2D-DFE), whose filters are optimized to jointly cancel noise, ISI, and MUI based on the MMSE criterion. For this receiver, by modeling the spreading sequences of the interfering users as random sequences, system bit error probability has been calculated using the Gaussian approximation. Our numerical results show that the 2D-DFE exhibits significant performance improvement... 

A traveling wave distributed mixer is studied. It is shown that increasing the drain-source capacitances in a distributed FET mixer simultaneously improves its conversion gain and noise figure. Besides, it is shown that proper loading of input and output elements can improve the device performance. The simulation results are well matched with the measurements and also with the results of the existing certified simulators. © 2002 IEEE  

Design of an Ultra-Wideband 3-dB quadrature (90°) Hybrid using ADS and HFSS softwares plus Measurement report are presented. Simultaneous Use of these two softwares lead to fast and accurate design procedure. The coupler is realized in broadside stripline and with the connection of coupled regions in tandem structure. The measured data agrees well with the expected values from simulations, and shows a good ultra wide bandwidth response over the frequency range of 1-10 GHz. Measurements showed an amplitude unbalance of ±1.5 dB, a phase unbalance of 90°±7° , and an isolation and a return loss characteristics of more than 14 dB over the frequency of 1 to 10 GHz  

An efficient ray tracing technique for channel modeling of an ultrawideband signal in 60 GHz band is introduced. In the usual method, field calculations at many frequencies must be done where has a high computational cost. We have introduced a novel method using Chebyshev polynomials interpolation to reduce the computational cost. Some propagation parameters such as gain and root mean square (RMS) delay spread are obtained and compared to the other method  

We derive, evaluate, and discuss upper bounds on ergodic and outage capacities for a three-node relay network. The considered relay network has ultra-wideband (UWB) radio channels between the source, destination, and relay nodes. The derived bounds indicate that ergodic and outage capacities of the considered UWB-linked network increase up to 300% when a relay between the source and the destination is used. Furthermore, the bounds indicate that there is an optimum position for the relay node between the source and the destination, where ergodic capacity is maximized. Our numerical results shows that for the non-line-of-sight (NLOS) scenario, with the same signal to noise ratio on all links,... 

In this paper we examine the transmission of two types of ultra-wideband (UWB) signals, multiband orthogonal frequency division multiplexing (MB-OFDM) and impulse radio ultra-wideband (IR-UWB), over single mode fiber at 1550 nm. In order to investigate the impact of optical components such as laser diode, external modulator and single mode fiber on UWB signals, we develop mathematical models for these components. These models are experimentally verified and corresponding numerical parameter values are obtained by experiment. Using these models we discuss the transmission of two types of UWB signals over single mode fiber. A new figure of merit namely distortion factor is defined. Using... 

Utilisation of reliable communication technologies for data communication is a key challenge in smart grids. Due to specific characteristics of offshore wind farms (OWFs), wireless data communications is of interest for supervisory control and data acquisition (SCADA) communication between wind towers. The ultra-wideband (UWB) communication technology is one of the state-of-the-art communication technologies suitable for inexpensive, low-data rate, outdoor, long-range, communication applications. However, in order to employ it in OWFs, its link modelling and performance must first be well analysed comprehensively. In this paper, the UWB communication channel is modelled in OWFs and with... 

A 1.8-v 13-bit 25MS/S pipelined analog-to-digital (A/D) converter was designed and simulated using 0.18um CMOS technology. The proposed new high speed low power class AB opamp makes it possible to achieve requirements of 13-bit resolution and settling in 12ns within 0.01% accuracy. An optimum architecture for noise and power consideration is also selected to reduce power. Total Power dissipation is about 82 mw from a single 1.8 v supply, where INL and DNL are 0.7 LSB and 0.6 LSB respectively. SNDR of 75.5 dB is achieved  

In smart grid research and particularly Offshore Wind Farms (OWFs), employing wireless data communications as a reliable technology for Supervisory Control and Data Acquisition (SCADA) communication between wind towers is of great interest. This paper introduces the Ultra-Wideband (UWB) communication system based on Pulse Position Modulation (PPM) for this intention. In this work, the UWB link is modeled in WOFs and performance of the UWB link subject to several metrics such as range-data rate, range-bit error rate (BER), and path loss are systematically and arithmetically assessed. The results prove UWB system as a promising inexpensive, but high performance approach for wireless SCADA...