Ajit K. Chaturvedi

A family of ISI-free polynomial pulses

A family of ISI free polynomial pulses that can have an asymptotic decay rate of t/sup -k/ for any integer value of k has been proposed. The proposed family provides flexibility in designing bandlimited pulses in accordance with the desired application, even after the roll-off factor /spl alpha/ has been chosen. Pulses obtained from this family have been found to be better than the currently known good pulses.

A New Framework for Constructing Mutually Orthogonal Complementary Sets and ZCZ Sequences

In this correspondence, new characterizations for the construction of zero correlation zone (ZCZ) sequences from mutually orthogonal Golay complementary sets (MOGCS) is presented. It is shown that the recursive construction of MOGCS is inherent in these characterizations. Previously known constructions of ZCZ sequences and MOGCS are shown to be special cases of this characterization. The notion of mutually orthogonal ZCZ sequence sets is also introduced

ISI-free pulses with reduced sensitivity to timing errors

We consider the linear combination of two ISI free pulses, the raised cosine (RC) and the recently proposed better than raised cosine (BTRC). We determine their optimum combination using the distribution of timing error. The obtained pulses perform better than RC and BTRC for fixed as well as randomly distributed timing errors.

Complete Mutually Orthogonal Golay Complementary Sets From Reed–Muller Codes

Recently Golay complementary sets were shown to exist in the subsets of second-order cosets of a q-ary generalization of the first-order Reed-Muller (RM) code. We show that mutually orthogonal Golay complementary sets can also be directly constructed from second-order cosets of a q-ary generalization of the first-order RM code. This identification can be used to construct zero correlation zone (ZCZ) sequences directly and it also enables the construction of ZCZ sequences with special subsets.

A low complexity symbol timing estimator for MIMO systems using two samples per symbol

A new algorithm for data-aided symbol timing estimation in multiple antenna systems is proposed. By utilizing the information about the transmitted pulse, the proposed method achieves better performance and lower computational complexity than the recently proposed discrete Fourier transform (DFT) based interpolation method. Further, the method needs only two samples per symbol which is half of the oversampling factor required by the DFT based interpolation method.

Acoustic echo cancellation using multiple sub-filters

We present the modeling of the acoustic echo path based on the process segmentation approach. A new algorithm is proposed using the concept of decomposing the long adaptive filter into low order multiple sub-filters. Simulation results show that the decomposed LMS adaptive algorithm significantly improves the convergence rate while keeping the steady state error almost the same as that of the original long adaptive filter.

Closed Form BER Expressions for BPSK OFDM Systems with Frequency Offset

This letter addresses the performance degradation caused by the presence of carrier frequency offset (CFO) in orthogonal frequency division multiplexing (OFDM) systems. Accurate closed form bit error rate (BER) expressions for BPSK-OFDM systems impaired by frequency offset are derived. The analysis is carried out for flat and frequency selective Rayleigh fading channels. Simulation results have been used to cross-check the accuracy of the theoretical analysis.

A new family of concurrent algorithms for adaptive Volterra and linear filters

A novel idea for introducing concurrency in least squares (LS) adaptive algorithms by sacrificing optimality has been proposed. The resultant class of algorithms provides schemes to fill the wide gap in the convergence rates of LS and stochastic gradient (SG) algorithms. It will be particularly useful in the real time implementations of large-order linear and Volterra filters for which both the LS and SG algorithms are unsuited.

Performance analysis of predetection EGC in exponentially correlated Nakagami-m fading channel

Using a Gil-Palaez lemma-based approach, we derive a general expression for the bit-error rate of a predetection equal gain combining receiver for coherent binary phase-shift keying modulation in exponentially correlated, Nakagami-m fading channel for an arbitrary number of branches. The obtained expressions are different for even and odd numbers of branches. Numerical results have been corroborated with simulations.

Application of computational geometry to multiuser detection in CDMA

The maximum-likelihood multiuser detection problem in code-division multiple-access is known to be an optimization problem with an objective function that is required to be optimized over a combinatorial decision region. Conventional suboptimal detectors relax the combinatorial decision region by a convex region, without altering the objective function to be optimized. We take an approach wherein the objective function is reduced to a form appropriate for the application of a polynomial complexity algorithm in computational geometry, while keeping the decision region combinatorial. The resulting detector allows a tradeoff between performance and computational complexity. The bit-error rate performance of the detector has been found to be better than the decorrelator and the linear minimum mean-square error detectors, for the same level of complexity.