Shafayat Abrar

Blind equalization of square-QAM signals: a multimodulus approach

By generalizing and modifying some existing cost-functions, we present two new, generic and efficient multimodulus families of blind equalization algorithms for use in higher-order quadrature amplitude modulation based digital communication systems. Proposed algorithms are shown to be capable of blindly equalizing and recovering carrier-phase at convergence speed much faster than existing counterparts on certain QAM sizes. We show that particular examples of the proposed cost-functions include a number of existing algorithms. We also provide detailed dynamic convergence analysis which is found in good conformation with those obtained from Monte-Carlo experiments.

An Adaptive Constant Modulus Blind Equalization Algorithm and Its Stochastic Stability Analysis

A constant modulus algorithm is presented for blind equalization of complex-valued communication channels. The proposed algorithm is obtained by solving a novel deterministic optimization criterion which comprises the minimization of a priori as well as a posteriori dispersion error, leading to an update equation having a particular zero-memory continuous Bussgang-type nonlinearity. We also derive a stochastic bound for the range of step-sizes for a generic Bussgang-type constant modulus algorithm. The theoretical result is validated through computer simulations.

Vertical Handover Necessity Estimation Based on a New Dwell Time Prediction Model for Minimizing Unnecessary Handovers to a WLAN Cell

In this work, we devise a vertical handover necessity estimation (HNE) method to minimize unnecessary handovers for a mobile node (MN) entering a WLAN cell. The method relies on a new model for prediction of dwell time and computation of certain threshold values. By comparing the predicted dwell time with those thresholds, a MN is able to make decision whether it should perform handover to a WLAN cell, while keeping the probability of handover failure and probability of unnecessary handover within bounds. Simulation results obtained from Monte-Carlo experiments prove validity of the proposed model. We also compare this model with existing models for minimizing unnecessary handovers. We further enhance the analytical model by incorporating the throughput gain in HNE and show that this can further optimize handover decision in heterogenous networks.

Blind Equalization of Cross-QAM Signals

This letter presents two new blind equalization algorithms that are specifically designed for cross-QAM signals. Proposed algorithms minimize the dispersion of the equalizer output with respect to single or multiple cross-shaped zero error contour(s). Simulations and analysis demonstrate the good performance of the proposed algorithms

Soft constraint satisfaction multimodulus blind equalization algorithms

In this letter, a new multimodulus algorithm for blind equalization of complex communication channels is derived by solving a constrained optimization problem with relaxation. The intersymbol interference (ISI) optimization and phase-recovery capabilities of the proposed algorithm are analyzed. It is shown from computer simulations that superior performance for the derived algorithm over Lins algorithm is obtained.

Adaptive Minimum Entropy Equalization Algorithm

We employ minimum entropy deconvolution principle for blind equalization of complex digital signals. In essence, we maximize the output energy, constrain the equalizer output not to exceed certain level and obtain an adaptive solution capable of opening a closed-eye with the recovery of true energy of signal. We provide evidence of good performance in comparison to existing adaptive methods, like CMA and its variants, through simulations.

Adaptive Solution for Blind Equalization and Carrier-Phase Recovery of Square-QAM

In this letter, we adaptively optimize the equalizer output energy to obtain a joint blind equalization and carrier-phase recovery solution. The resulting (multimodulus) update algorithm possesses a particular zero-memory Bussgang-type nonlinearity. We provide evidence of good performance, in comparison to existing adaptive methods, like RCA, MMA and CMA, through computer simulations for higher-order quadrature amplitude modulation signalling on symbol- and fractionally-spaced channels.

New multimodulus blind equalization algorithm with relaxation

A new multimodulus algorithm is presented for blind equalization of complex-valued communication channels. The proposed algorithm is obtained by solving a novel deterministic optimization criterion that constituted the dispersion minimization of a priori as well as a posteriori quantities, leading to an update equation having a particular zero-memory continuous nonlinearity. Analyses of automatic phase-recovery and interference cancellation capabilities of the proposed algorithm are provided

Steady-state performance of multimodulus blind equalizers

Multimodulus algorithms (MMA) based adaptive blind equalizers mitigate inter-symbol interference in a digital communication system by minimizing dispersion in the quadrature components of the equalized sequence in a decoupled manner, i.e., the in-phase and quadrature components of the equalized sequence are used to minimize dispersion in the respective components of the received signal. These unsupervised equalizers are mostly incorporated in bandwidth-efficient digital receivers (wired, wireless or optical) which rely on quadrature amplitude modulation based signaling. These equalizers are equipped with nonlinear error-functions in their update expressions which makes it a challenging task to evaluate analytically their steady-state performance. However, exploiting variance relation theorem, researchers have recently been able to report approximate expressions for steady-state excess mean square error (EMSE) of such equalizers for noiseless but interfering environment.In this work, in contrast to existing results, we present exact steady-state tracking analysis of two multimodulus equalizers in a non-stationary environment. Specifically, we evaluate expressions for steady-state EMSE of two equalizers, namely the MMA2-2 and the βMMA. The accuracy of the derived analytical results is validated using different set experiments and found in close agreement. HighlightsWe provide performance analysis of two multimodulus blind equalizers.The analysis evaluates EMSE performance in both stationary and non-stationary environments.The analysis can provide the optimal equalizer length for the given channel and step-size.We validate our analytical findings for both fixed and time-varying channels.

Compact constellation algorithm for blind equalization of QAM signals

A new algorithm is presented for the blind equalization of complex signals. This algorithm combines the benefits of the well-known reduced-constellation algorithm (RCA) and decision-directed algorithm (DDA). The contribution lies in the technique of incorporating the sliced symbols (outcome of the decision device) in the weight adaptation process. Unlike the RCA, where the reduced constellation contains only four symbol points, the proposed algorithms uses all symbols of the signal constellation by compacting them in some statistical manner. The steady-state characteristics of the proposed algorithm are demonstrated by way of simulations and are compared to those of RCA. It is observed that the new algorithm has a better steady-state performance than RCA.