Hasan Amca

Channel estimation using short training sequences

The estimation of the impulse responses of time-variant mobile radio channels is a challenging issue in mobile communication systems. For CDMA systems, it is generally assumed that the receiver knows the corresponding spreading sequences. A maximum likelihood channel estimation method, which uses the known spreading sequences together with short training sequences, is considered for synchronous CDMA systems.

The adaptive path selective decorrelating detector

In this paper, the multipath decorrelating (MD) detector which is used in code division multiple access (CDMA) systems to eliminate multiple access interference (MAI) is considered. The MD detector requires the inversion of a signature sequence correlation matrix. This process is computationally expensive and it also enhances the channel noise. Recently, an adaptive path selective decorrelating (APSD) detector has been proposed to reduce both the computational complexity and noise enhancement at a marginal increase in residual MAI due to unselected paths. The APSD detector requires the channel knowledge. In practice, the channel coefficients are not known and must be estimated. Although several channel estimation methods exist for CDMA systems, a maximum-likelihood approach using short preamble sequences is adopted in this paper. The estimation process has an impact on the overall system performance by introducing estimation errors in actual channel coefficients. Therefore, this paper proposes a semi-analytic method to analyze the performance of the APSD detector in the presence of those channel estimation errors. Extensive simulations are carried out and reported to show tradeoffs for different system parameter settings.

Iterative near---far resistant channel estimation by using a linear minimum mean squared error detector

Channel estimation techniques for CDMA system need to combat multiple access interference (MAI) to improve the estimation performance. The linear MMSE detector has certain advantages with respect to the near–far problem and can be used to develop a channel estimation algorithm. In this paper, an efficient iterative method for near–far resistant single-user mobile radio channel estimation in slow fading multi-path direct sequence code division multiple access (DS-CDMA) channels is presented. Computer simulation results demonstrate that a significant performance improvement can be achieved with the proposed method especially under extreme near–far conditions.

Performance Analysis of Adaptive Path Selective Decorrelating Detector with Channel Estimation Errors

The system complexity and noise enhancement due to the use of Multipath Decorrelating Detector (MDD) can be reduced by employing adaptive path selection technique. Adaptive Path Selective Decorrelating Detector (APSDD) requires knowledge of the channel coefficients for path selection. Generally, the channel coefficients are assumed to be known at the receiver. However, this is not realistic and the channel coefficients should be estimated. In this paper, we extend the Bit Error Rate (BER) analysis of the path selective receiver to include channel estimation errors.

Using Mobile Telephone as an Operator Independent, Secure Micro-Payment Tool

-With the latest advances in Information and Communication Technologies (ICT), using different technologies for electronic-payment has become a major issue in the retail market. The use of portable communication devices became particularly attractive candidates when versatility, security and simplicity features of payment technologies are considered.

Iterative Least Squares Channel Estimation in Frequency Selective CDMA Systems

Multiple access interference (MAI) is the main factor affecting the performance of channel estimation techniques for code division multiple access (CDMA) systems. Although, several multi-user channel estimation algorithms have been proposed to mitigate MAI, these algorithms require high computational complexities. In this paper, we address the problem of least squares (LS) mobile channel estimation at high channel efficiency that requires a short training sequence along with the spreading sequences. Then, we employ an efficient iterative method based on conjugate gradient (CG) algorithm to reduce the computational complexity of the estimation method. Computer simulations illustrate that the proposed method performs almost identical to the exact LS estimate for reasonable training lengths.

Training Sequence Aided Signature Waveform Estimation

In code division multiple access channels multiuser detection techniques are known to be effective strategies to counter the presence of multiuser interference towards improving spectral efficiency. Generally, multiuser detectors can provide excellent performance only when the signature waveforms of all users are precisely known. Hence, the estimation of signature waveforms is a challenging issue in mobile communication systems. In this paper, we compare the performance of two short training sequence aided signature waveform estimators. One is maximum likelihood type signature waveform estimator that requires the knowledge of spreading sequences and short training sequences. The other estimator is recently proposed based on subspace method and requires the knowledge of training sequences only. Through the simulations, we show the signature waveform estimation performance of both systems and the effect of the estimation error on the performance of a multiuser detector. The complexity comparisons of both systems are also given.

Impact of impulsive noise on millimeter wave cellular systems performance

Millimeter wave (mmWave) communication is a resplendent technology for the Fifth Generation (5G) systems. This outdoor cellular system, 5G, is expected to provide internet connections 40 times faster and with at least four times more coverage worldwide than the current 4G Long Term Evolution (LTE) wireless communications standard. However, mmWave communication system performance could be degraded severely by the non-Gaussian Impulsive Noise (IN) and this will create a cruel task to mitigate such harmful effect and modify the impairments in the system. In this paper, blanking and clipping filters are utilized in order to enhance the capability of the communication system in suppressing IN. The problem of receiver design for large antenna arrays at both the base station and mobile station in the presence of IN is modeled using Gaussian mixture model. The results reveal that the proposed algorithms of blanking and clipping are able to minimize the bit error rate.

An adaptive least squares channel estimation based on conjugate gradient approach for multipath fading CDMA systems

Multiple access interference (MAI) is the main factor affecting the performance of channel estimation techniques for code division multiple access (CDMA) systems. Although, several multi-user channel estimation algorithms have been proposed to mitigate MAI, these algorithms require high computational complexities. In this paper, we address the problem of iterative least squares (LS) mobile channel estimation at high channel efficiency that requires a short training sequence along with the spreading sequences. We employ an efficient iterative method based on conjugate gradient (CG) algorithm to reduce the computational complexity of the estimation method. Computer simulations illustrate that the proposed method performs almost identical to the exact LS estimate for reasonable training lengths.