S. M. Sameer

Smart glove with gesture recognition ability for the hearing and speech impaired

With the advent of wearable technology, it is now possible to implement numerous and extremely creative ideas to serve humanity in unprecedented ways. Thus inspired, we have developed a smart system which would be able to serve as best friend to the hearing and speech impaired person. The primary goal of this paper is to design and implement a low cost wired interactive glove, interfaced with a computer running MATLAB or Octave, with a high degree of accuracy for gesture recognition. The glove maps the orientation of the hand and fingers with the help of bend sensors, Hall Effect sensors and an accelerometer. The data is then transmitted to a computer using automatic repeat request (ARQ) as an error controlling scheme. The system is modeled for the differently abled section of the society to help convert sign language to a more human understandable form such as textual messages.

Fast communication: An efficient technique for the integer frequency offset estimation in OFDM systems

This communication proposes a novel null subcarrier based algorithm for the integer frequency offset (IFO) estimation in orthogonal frequency division multiplexing (OFDM) systems. Bandwidth overhead of the proposed algorithm is less than 5% of the bandwidth of first OFDM symbol in a frame. The IFO is estimated by computing the energy of subcarriers at the DFT output just once and by finding the shift in null subcarrier indices using a simple statistical approach. The proposed method is computationally very efficient as compared to the methods which use exhaustive search procedures. It also achieves advantages over a few recently published methods in terms of the number of real additions (RAs) and bandwidth overhead required for IFO estimation. Computer simulation studies show that the estimator is able to achieve an IFO estimation range equal to the OFDM bandwidth.

Pilot-Aided Joint Estimation of Doubly Selective Channel and Carrier Frequency Offsets in OFDMA Uplink With High-Mobility Users

In this paper, we propose a novel pilot-aided joint channel and carrier frequency offset (CFO) estimation method for orthogonal frequency-division multiple access (OFDMA) uplink systems with users operating in time- and frequency-selective (doubly selective) fading environments. We use Bernstein basis polynomials (BBPs) to capture rapid time variations of the channel, which avoids the identifiability issue in estimating large number of actual channel coefficients. We make use of space-alternating generalized expectation-maximization maximum a posteriori probability (SAGE-MAP) algorithm for the joint estimation of CFOs and channel coefficients. The convergence properties of the proposed method is assessed and proved analytically. The exact Bayesian Cramér-Rao bound (BCRB) for the MAP estimation problem is also derived and is shown to be comparable to the mean squared error (MSE) of the proposed technique.

A hybrid joint ML technique for CFO, timing offset, and channel estimations in an OFDMA uplink

In this paper, we propose a novel hybrid joint maximum-likelihood estimator for carrier frequency offset CFO, timing offset, and channel response of all users in the uplink of an orthogonal frequency division multiple access OFDMA system. The proposed estimation method significantly reduces complexity of this multiparameter, multidimensional optimization problem, using the concept of separation of the different user signals by means of newly defined projection operators. This projection technique is combined with the alternating projection method available in the literature to arrive at a new hybrid algorithm that offers significant performance advantages in terms of computational complexity and estimator performance. The joint estimation of the CFOs, timing offsets, and channel coefficients for all active users together at the base station of the OFDMA uplink is a rarely addressed task. The proposed method also offers the flexibility of application to any subcarrier assignment scheme used in OFDMA systems. Extensive simulation studies corroborate the advantages of the new hybrid method for all three estimation requirements in the multiuser OFDMA uplink. Copyright

On the computation of exact moments and performance metrics for multihop transparent weibull relay channels

In this paper, exact expressions are derived for the moments and performance metrics for a compound channel in multi-hop transmissions with transparent relays over independent and not necessarily identically distributed Weibull fading channels. Firstly, various moments are derived using characteristic function of second kind, based on Mellin transform. Using these moments, two useful statistical performance metrics named coefficient of variation and amount of fade are also derived for the end to end system. Moments and the metrics derived are in tractable compact forms and can be easily extended to other distributions also. These results can be directly applied in the study of outage probability and average bit error probability of such multi-hop transmissions. The proposed mathematical analysis is complimented by various numerical results, demonstrating the impact of the proposed expressions

Iterative Joint Carrier Frequency Offset and Doubly Selective Channel Estimation in High-Mobility MIMO-OFDMA Uplink Using Oblique Projection

In this paper, we propose a novel pilot aided joint estimation technique for carrier frequency offset (CFO) and doubly selective (both time and frequency selective) channel (DSC) in high-mobility multiple-input-multiple-output orthogonal frequency-division multiple-access (MIMO-OFDMA) uplink systems. As the maximum-likelihood (ML) solution to this estimation problem is highly computationally tedious due to the requirement of multidimensional optimization, we propose an iterative scheme based on the oblique projection (OP), which separates the user signal in each iteration, resulting in decomposition of highly complex multidimensional search to many 1-D searches. We also derive a low-complexity approximation to the proposed technique, which makes use of precalculated projection matrices stored at the base station. The exact Cramer-Rao bound (CRB) of the joint estimation of CFOs and DSCs in MIMO-OFDMA uplink is also derived. Simulation studies indicate that the mean square error performance of the proposed techniques nearly achieves the CRB even at low signal-to-noise ratios (SNRs).

Joint ML Estimation of CFO and Channel, and a Low Complexity Turbo Equalization Technique for High Mobility OFDMA Uplinks

In this paper, we propose a pilot aided joint estimation technique for carrier frequency offsets (CFOs) and doubly selective channels (DSCs), and a low complexity turbo equalization (TE) scheme for orthogonal frequency division multiple access (OFDMA) uplink systems with high mobility users. We propose the use of Chebyshev polynomials of the first kind (CPF) for accurately representing the DSCs. As the exact solution to the estimation problem is computationally intensive, we make use of space alternating generalized expectation maximization (SAGE) algorithm, that replaces the complex multidimensional search with many one dimensional searches. We derive the exact Cramer-Rao bound (CRB) of the joint estimation problem and the mean squared error of the proposed estimation technique is shown to be closely comparable to it. The convergence characteristics are also studied and it is proved analytically that the proposed method converges. Additionally, we propose a low complexity turbo equalization method with iterative multiple access interference (MAI) cancellation, which uses the soft feedback symbol estimate for removing the MAI and self inter-carrier interference (ICI) in each iteration. Our proposed estimation and equalization technique can be applied to any type of carrier assignment scheme (CAS) in OFDMA and offers very good performance even at high mobile speeds.

Firefly Algorithm for Joint Estimation of Frequency Offsets and Channel in OFDMA Uplink

This paper addresses the problem of joint maximum-likelihood estimation of carrier frequency offsets, and channel responses in an orthogonal frequency division multiple access (OFDMA) uplink, which is a computationally-intensive, multiparameter, multidimensional problem. We propose to apply a recently-developed meta-heuristic algorithm called the firefly algorithm (FA) for the estimation of required parameters. We also introduce a new initialization procedure for the FA algorithm based on the separability of cost functions, which drastically reduces its computational complexity. A separate pilot OFDMA symbol is transmitted prior to the data symbols to estimate the parameters. The proposed technique is shown to achieve excellent performance at reduced computational complexity, especially at low signal-to-noise ratio. Also, it can be applied to OFDMA systems with any type of carrier assignment schemes. The significant features of the proposed estimation method are substantiated through extensive computer simulation studies and are compared with an important classical estimation technique available for the problem, to highlight its superiority.

A joint ML estimation technique for timing, CFO and channel for OFDMA uplink transmissions

This paper addresses the issue of joint maximum-likelihood (ML) estimation of carrier frequency offset (CFO), timing error and channel response for OFDMA uplink transmissions. A pilot preamble-based approach is proposed that makes use of the concept of signal decomposition. Earlier works have demonstrated that it is possible to decompose the multidimensional optimization involved in this joint estimation into a series of one-dimensional searches. The alternating projection (AP) algorithm is effectively used to determine the ML solution to this problem in many earlier works. In this work, we propose a new method of signal decomposition that can be combined with the conventional AP method to arrive at better parameter estimates. It achieves better performance in lesser number of estimation cycles and hence with lesser computational load. Another advantage is that it offers the flexibility of application to any generalized subcarrier assignment scheme in OFDMA systems. The performance advantages of this new method are substantiated through simulation studies.

An Efficient Maximum Likelihood Carrier Frequency Offset Estimator for OFDM Using Null Subcarriers and Cyclic Prefix

Accurate estimation of carrier frequency offset (CFO) is an important requirement in orthogonal frequency-division multiplexing (OFDM) based wireless communication systems. In this paper, we propose a hybrid procedure to accomplish this task efficiently. One of the key importance of the approach is the judicious combination of two independent estimators so as to reduce the bandwidth overhead and computational complexity over many conventional methods. It employs the cyclic prefix and a few null subcarriers, respectively, for the fractional and integer frequency offset estimations. We also propose a novel null subcarrier allocation scheme based on Fibonacci series. The range of frequency offset that can be estimated by the proposed technique is equal to the full OFDM bandwidth. Furthermore, performance of the proposed CFO estimator is mathematically analyzed by deriving an expression for the bit error probability of the receiver under Rayleigh fading channel and the Cramer-Rao lower bound for the mean square estimation error. For moderate SNRs, our approach is shown to greatly outperform some recently published methods in terms of BER performance, bandwidth overhead and receiver complexity.