Abhijeet Bishnu

Iterative Time-Domain-Based Sparse Channel Estimation for IEEE 802.22

This letter proposes an iterative algorithm for sparse channel estimation for IEEE 802.22-based communication system in time-domain. The proposed algorithm initially estimates the active channel taps with the help of cross-correlation of received signal and transmitted preamble. Then an iterative algorithm comprised of adaptive thresholding and least mean square is used in time domain for sparse channel estimation. A modified Wiener filter for sparse channel is used to validate the mean square error performance of the proposed algorithm. Simulation results for various standardized sparse channel models show robustness of the proposed algorithm over others.

Sparse Channel Estimation for Interference Limited OFDM Systems and Its Convergence Analysis

Wireless communication channels are highly prone to interference in addition to the presence of additive white Gaussian noise (AWGN). Stochastic gradient (SG)-based non-parametric maximum likelihood (NPML) estimator, gives better channel estimates in the presence of Gaussian mixture (AWGN plus interference) noise processes, for subsequent use by the channel equalizer. However, for sparse channels, the SG-NPML-based channel estimator requires large iterations to converge. In this paper, we propose a natural gradient (NG)-based channel estimator for sparse channel estimation in the presence of high interference. We propose a generalized

Natural gradient non-parametric maximum likelihood algorithm for sparse channel estimation in non-Gaussian noise

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On performance analysis of IEEE 802.22 (PHY) for COST-207 channel models

th order warping transformation on channel coefficients space and then calculate the Riemannian metric tensor, thereby resulting in faster convergence in interference limited channels. The proposed algorithm is applied for IEEE 802.22 (based on orthogonal frequency division multiplexing) channel estimation in the presence of interference. Extensive simulations and experimental results show that the proposed NG-based algorithm converges faster than SG-NPML for the same mean squared error (MSE) floor with similar computational complexity per iteration as an SG-NPML algorithm. We also present convergence analysis of proposed NG-NPML algorithm in the presence of Gaussian mixture noise and derive an analytical expression for the steady-state MSE.

An IEEE 802.22 transceiver framework and its performance analysis on software defined radio for TV white space

The stochastic gradient (SG) based non-parametric maximum likelihood (NPML) adaptive algorithm gives better channel estimation as compared to least squares in the presence of additive non-Gaussian noise. However, SG-NPML based channel estimator requires large number of iterations to converge for sparse channels. Natural gradient (NG) based adaptive algorithms are known to converge faster as compared to SG algorithms when the channel coefficients are warped into a known Riemannian structure with respect to Euclidean space, and performs well in sparse channel. In this paper, we propose a quadratic warping transformation on channel coefficients space and then calculate the Riemannian metric tensor that describes the local curvature of coefficient space. The proposed approach is applied for sparse channel estimation for orthogonal frequency division multiplexing (OFDM) based receiver in the presence of interference (modelled as non-Gaussian process) and simulation results show that the proposed NG based NPML algorithm converges faster than conventional SG-NPML for the same mean square error (MSE) floor.

Cognitive Radio Networks: IEEE 802.22 Standards

With rapid increase in demand for bandwidth, several researchers around the world have found that, majority of licensed bands are either unused or underused. These under-utilised bands allocated for TV transmission are known as TV white space (TVWS). The IEEE 802.22 wireless regional area network (WRAN) is the latest standard for effective utilization of TV bands. This standard is based on orthogonal frequency division multiplexing (OFDM) with different cyclic prefix and modulation techniques. In this paper, we analyse the performance of IEEE 802.22 on different environments such as rural area (RA), typical urban (TU) and hilly terrain (HT) of COST-207 channel models. The performance analysis has been done for different modulation techniques, without channel coding, with channel coding of rate 1/2, punctured channel coding and comparison is drawn for Viterbi decoder and simplified logdomain sum-product algorithm based low density parity check (LDPC) decoder. We have also done separate analysis of digital TV (DTV) interference on customer premise equipments of IEEE 802.22 standard for TU model. The analysis will be useful for both academic and industry researchers and practitioners.

LogDet Covariance Based Spectrum Sensing Under Colored Noise

With rapid increase in new applications and services, there is huge demand for internet bandwidth. Several researchers around the world have found that, majority of licensed bands (mostly terrestrial TV band) are either unused or underused. These underutilized bands allocated for TV transmission are known as TV white space (TVWS). For effective utilization of TVWS, the IEEE 802.22 is proposed. The IEEE 802.22 wireless regional area network (WRAN) is the latest standard for effective utilization of TV bands. This standard is based on orthogonal frequency division multiplexing with various modulation techniques to provide different data rates. In this paper, an implementation framework for physical layer of IEEE 802.22 WRAN standard for normal mode is demonstrated and analyzed. This transceiver is implemented using the National Instruments Laboratory Virtual Instrument Engineering Workbench programming software on the National Instruments universal software radio peripheral 2952R. We have also analyzed different blocks of IEEE 802.22 based on their execution time, and identify the critical blocks of IEEE 802.22 that should be optimized for real-time applications for commercial product development and field deployments. We have also highlighted the difference between theoretical and practical performance of the considered error control codes for IEEE 802.22 specified block size. Additionally, various covariance based spectrum sensing methods are also analyzed for real-world environment.