R. C. Jain

An adaptive notch filter for narrow band interference removal

A modification on an existing algorithm to dynamically adapt to interfering signal frequency and its magnitude is given. The algorithm first detects the presence of the interfering signal in real time and if present, it adjusts parameters to maximize the signal to noise ratio at the output. The AWGN and interfering signal power is taken in a wide dynamic range - up to 20 dB and 80 dB respectively. The proposed IIR filter detects and almost perfectly removes the interference.

A Simple Closed form Approximation of Average Channel Capacity for Weakly Turbulent Optical Wireless Links

Performance of optical wireless link is degraded by the presence of atmospheric turbulence induced fading. In this paper, a simple tight closed form expression for average channel capacity of optical wireless communication (OWC) system in weak atmospheric turbulence is given. The channel capacity of OWC systems employing spatial diversity reception with maximum ratio combining and equal gain combining over independent and identical turbulence induced fading channels is also computed using proposed expression. Results computed by employing our expressions are in excellent agreement with results based on numerical Monte Carlo simulations over permissible turbulence strength for a wide range of signal to noise ratio.

Effect of aperture averaging and spatial diversity on capacity of optical wireless communication systems over lognormal channels

In this paper it is evaluated average channel capacity of an optical wireless communication system with aperture averaging and diversity reception over lognormal channels using a simple approximate closed form expression. The qualitative improvement in channel capacity is compared and investigated for various turbulence mitigation techniques: namely aperture averaging, diversity techniques such as maximal ratio combining and equal gain combining. Based on our study it is found that aperture averaging gives reasonably improved performance as compared to both types of diversity reception beyond certain turbulence strength. However, irrespective of turbulence strength, substantial improvement in capacity may be achieved with an array of direct detection receivers. Results obtained using the proposed expressions are in excellent agreement with those based on Monte Carlo simulations.

Fast windowed update algorithm for ODCT computation

In this paper algorithms capable for independent updating the type-II Odd Discrete Cosine Transform (ODCT-II) and type-II Odd Discrete Sine Transform (ODST-II) coefficients of a real-time windowed data sequence are proposed. The update algorithm is developed for split-triangular windowed input data. This windowing function reduces ringing effect encountered in rectangular windowing function. The computational complexity of developed algorithm is O(N). Proposed algorithm will further reduce the memory requirements significantly as we do not need to compute ODST coefficients while updating ODCT coefficients. These set of algorithms will be useful in applications where we need only the ODCT coefficients or only ODST coefficients. The analytically developed algorithms have been tested by Matlab implementation.

A Novel MMSE Based Predictive Method for Narrow Band Interference Removal

A new system model based on state space representation of the received signal for Narrow-band interference suppression in Direct Sequence-Spread Spectrum (DS-SS) system is given. This model recursively estimates the interfering signal in the presence of desired information and white Gaussian noise. To further improve the performance, we employ MMSE criteria to estimate the transmitted symbols. The MMSE estimate requires low computational complexity than Code-aided techniques. Our simulation results demonstrate that this technique provides better SINR improvement over to Nonlinear predictor, Linear predictor, Kalman-Bucy predictor for-65 dB to-5 dB input SINR and up to 10 dB AWGN power. For high interfering signal and noise power, our results clearly show that our SINR improvement performance exceeds the SINR improvement upper-bound calculated for the prediction based techniques. Besides reducing the effect of interfering signal, our technique also reduces AWGN noise. Our model also provides better BER performance than Nonlinear predictor.

Performance Comparison of Sine and Cosine Phased BOC Signals Used for Radionavigation

Abstract In this paper, we give the relative performance of sine and cosine phased Binary Offset Carrier (BOC) signals used for global navigation satellite systems (GNSS). An expression for the power spectral density of cosine phased BOC is derived and its performance is compared with that of sine phased BOC. Comparing the PSD and the bandwidth of the various BOC signals, it is demonstrated that the performance of cosine phased BOC in terms of frequency offset and code tracking accuracy is better than that of sine phased BOC. It is also found that cosine BOC gives better spectral separation as compared to sine BOC in some cases.

A New Closed Form Approximation for BER for Optical Wireless Systems in Weak Atmospheric Turbulence

Abstract Weak atmospheric turbulence condition in an optical wireless communication (OWC) is captured by log-normal distribution. The analytical evaluation of average bit error rate (BER) of an OWC system under weak turbulence is intractable as it involves the statistical averaging of Gaussian Q-function over log-normal distribution. In this paper, a simple closed form approximation for BER of OWC system under weak turbulence is given. Computation of BER for various modulation schemes is carried out using proposed expression. The results obtained using proposed expression compare favorably with those obtained using Gauss-Hermite quadrature approximation and Monte Carlo Simulations.

Capacity of Optical Wireless System over Log-Normal Channels with Spatial Diversity in Presence of Atmospheric Losses

Abstract In this paper, average channel capacity of optical wireless communication system is evaluated under the combined effect of geometrical loss, attenuation due to weather conditions and weak atmospheric turbulence using a simple closed form expression. Fading induced due to atmospheric turbulence is modeled by log-normal distribution. Considering the fact that the sum of log-normal random variables can be well approximated by another log-normal random variable, the proposed expression has been utilized to compute the channel capacity for spatial diversity reception employing maximum ratio combining and equal gain combining over uncorrelated turbulence-induced fading conditions. It is shown that spatial diversity is an effective technique to mitigate the impairments caused by various atmospheric conditions such as haze, rain and fog. The quantitative improvement in channel capacity achieved by using diversity techniques is investigated and compared. Accuracy of the results is validated with exact results computed using Monte Carlo simulation.

An Approximation for BER of Optical Wireless System under Weak Atmospheric Turbulence using Point Estimate

Abstract Obtaining analytically closed-form expression for bit error rate (BER) of an optical wireless communication (OWC) system under weak atmospheric turbulence is extremely difficult and intractable. In this paper, a simple closed-form approximate expression for average BER of OWC system under weak turbulence condition is obtained using point estimate method. The proposed expression is used to compute the BER for on-off keying (OOK) and sub carrier intensity modulated (SIM) binary phase shift keying (BPSK) modulation schemes. Results obtained using proposed expression are compared with those obtained using Gauss-Hermite quadrature approximation and Monte-Carlo simulations.