Performance evaluation of OFDM schemes over multipath fading channels

This paper discusses the transmission of the orthogonal frequency division multiplexing (OFDM) signal through the multipath fading indoor channel and its capability to combat the intersymbol interference (ISI) as well as its effective implementation with the discrete Fourier transform is described. The channel model used was based on Saleh-Valenzuela model with lognormal fading distribution of gain amplitudes. Simulation modules were developed and the effect of the multipath on the OFDM system performance with BPSK, QPSK, 16PSK, 64PSK, 16QAM, 64QAM, and 128QAM modulations was evaluated in terms of the bit error rate (BER) as a function of the energy per bit-to-noise ratio (EBNR). The influence of the number of carriers as well as the guard interval duration on the performance was also investigated. Simulations showed that the EBNR required to achieve a certain BER is significantly increased by 8-10 dB for dense multipath fading channels over that required in AWGN channels. These performance measures are useful for the design and assessment of high speed indoor wireless communication systems

Spatial and temporal fading correlation of uniform linear antenna array in three-dimensional signal scattering

In practice, diffraction and scattering from oblique surfaces create waves that travel in three-dimensional (3-D) space and arrive at the receiver with both azimuth and elevation angles. In this paper, 3-D signal scattering is considered. Generalized analytical expressions for the spatial and temporal signal fading correlations are derived, and numerically evaluated, for a uniform linear array (ULA) in terms of the antenna elements spacing and statistical distributions of the angles of arrival (AOAs). The results show that the effect of the elevation angle distribution on the spatial correlation values in case of vertically separated antenna elements is much more significant than that on horizontally separated antenna elements

Time-domain RLS-based channel estimation for MIMO OFDM systems

In this paper, an adaptive channel estimation scheme for MIMO OFDM systems based on time-domain training and recursive least squared (RLS) algorithm is proposed. Time orthogonal as well as simultaneously transmitted training sequences are considered. The channel is assumed to be slowly varying time-dispersive, i.e., constant during one OFDM symbol but changing from symbol to symbol. Channel estimation is performed in time-domain followed by zero-forcing equalization in the frequency-domain. The computational complexity is significantly reduced by applying the matrix inversion lemma. Simulation results show that the proposed estimator with time orthogonal training sequences has better estimation performance over a range of Doppler spreads compared to the case when the training sequences are simultaneously transmitted from the different transmit antennas

RLS channel estimation and tracking for MIMO-extended IEEE 802.11a WLANs

Wireless communication systems based on multiple-input multiple-output (MIMO) technology and orthogonal frequency division multiplexing (OFDM) have the potential to achieve enormous increase in the capacity and link reliability. In order to realize such systems, channel estimation is crucial. In this paper, an adaptive channel estimation and tracking scheme based on recursive least squares (RLS) algorithm is proposed for MIMO OFDM-based wireless local area networks (WLANs). Preamble-aided channel estimation is performed in time-domain (TD). The estimator is then extended to perform decision-directed (DD) channel tracking during data transmission. The channel is assumed to be constant during one OFDM symbol and evolving in time according to the first-order Markov process. Different training rates at different Doppler frequencies were investigated. Simulation results show that the proposed estimation scheme has excellent performance measured in terms of the mean squares error (MSE) and the bit error rate (BER), provided that the forgetting factor of the RLS algorithm is optimally selected

MIMO OFDM channel estimation based on RLS algorithm: the time- versus frequency-domain implementations

In this paper, exponentially-weighted recursive least squared (EW-RLS) channel estimation for multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems is investigated. Channel estimation in time-domain (TD) as well as frequency-domain (FD) is investigated through exploiting preambles and pilot symbols inserted in TD and FD, respectively. The channel is assumed to be slowly time-varying frequency-selective, constant during one OFDM symbol but changing from symbol to symbol. Simulation results show that the TD EW-RLS estimator has better estimation performance in terms of the mean-squares error (MSE) and bit-error rate (BER), compared to FD EW-RLS estimation approach. The computational complexity is significantly reduced by recursively updating the channel estimates and by applying the matrix inversion lemma

Time-domain adaptive channel estimation for OFDM-based WLAN with multiple-antennas

In this paper, an adaptive time-domain (TD) channel estimation scheme, based on recursive least squares (RLS) algorithm, is proposed for multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) based wireless local area networks (WLANs). The estimator is then extended to perform decision-directed (DD) channel tracking during data transmission. The channel is assumed to be constant during one OFDM symbol but evolves in time according to the first-order Markov process. Different training rates at different Doppler frequencies were investigated. Simulation results show that the proposed estimation scheme has excellent performance measured in terms of the mean squares error (MSE) and the bit error rate (BER), provided that the forgetting factor of the RLS algorithm is optimally selected

International Nosocomial Infection Control Consortiu (INICC) report, data summary of 43 countries for 2007-2012. Device-associated module

We report the results of an International Nosocomial Infection Control Consortium (INICC) surveillance study from January 2007-December 2012 in 503 intensive care units (ICUs) in Latin America, Asia, Africa, and Europe. During the 6-year study using the Centers for Disease Control and Prevention's (CDC) U.S. National Healthcare Safety Network (NHSN) definitions for device-associated health care–associated infection (DA-HAI), we collected prospective data from 605,310 patients hospitalized in the INICC's ICUs for an aggregate of 3,338,396 days. Although device utilization in the INICC's ICUs was similar to that reported from ICUs in the U.S. in the CDC's NHSN, rates of device-associated nosocomial infection were higher in the ICUs of the INICC hospitals: the pooled rate of central line–associated bloodstream infection in the INICC's ICUs, 4.9 per 1,000 central line days, is nearly 5-fold higher than the 0.9 per 1,000 central line days reported from comparable U.S. ICUs. The overall rate of ventilator-associated pneumonia was also higher (16.8 vs 1.1 per 1,000 ventilator days) as was the rate of catheter-associated urinary tract infection (5.5 vs 1.3 per 1,000 catheter days). Frequencies of resistance of Pseudomonas isolates to amikacin (42.8% vs 10%) and imipenem (42.4% vs 26.1%) and Klebsiella pneumoniae isolates to ceftazidime (71.2% vs 28.8%) and imipenem (19.6% vs 12.8%) were also higher in the INICC's ICUs compared with the ICUs of the CDC's NHSN