Cesar A. Medina

Performance comparison of minimum variance single carrier and multicarrier cdma receivers

This work provides comparisons between CDMA-based multiple access systems in a single and multicarrier fashion. Both zero padding and cyclic prefix types of guard intervals are considered. Comparisons include different performance measures such as signal-to-interference plus noise ratio (SINR), bit error rate (BER), and robustness against channel order overestimation. We also address the effects of finite number of samples when estimating the detector filter. In order to allow a fair comparison, blind detection based on the minimum variance is assumed for all considered systems. It is shown through computer simulations that multicarrier CDMA performs better than single carrier CDMA and is more robust against channel order overestimation.

Channel Estimation for RLS-Based Linearly Constrained Minimum Variance Receivers

In this paper we use an alternative implementation of the RLS based linearly constrained minimum variance (LCMV) receiver for multicarrier (MC) CDMA systems. As a result of this implementation a new blind channel estimation algorithm is proposed. It is shown through computer simulations that the resulting receiver filter achieves nearly the same performance than previously proposed methods, while reduces the computational complexity.

Nonassisted adaptive algorithm for data fusion in distributed detection systems [Correspondence]

In this work we propose a nonassisted adaptive fusion algorithm to perform data detection in distributed systems with a decode-then-fuse (DtF) type of receiver. Different from previously proposed fusion rules, where channel and nodes statistics are needed, the proposed algorithm adapts its weights and decision threshold based only on the received signals, so that time-varying scenarios or inhomogeneous systems are well suited. Computer simulations show that the proposed adaptive fusion strategy exhibits a performance very close to that of the optimal fusion rule.

Playing with Blocks: A New Combination of Block Transmission and the CDMA Multiple Access Technique

This paper proposes a combination of the Single Carrier (SC) block transmission and the Code Division Multiple Access (CDMA) technique. Performance comparisons with the traditional SC DS- CDMA block transmission system are presented. A key feature of the proposed transmission technique is that, unlike SC DS-CDMA transmissions, the original code orthogonality between users is preserved despite propagation through multipath frequency selective channels, thus ideally allowing the decoupling of the signals at the receiver side. Besides this advantage, and mostly due to it, the performance results indicate a clear superiority of the proposed system over the traditional SC DS-CDMA. The simulation results consider frequency domain MMSE (Minimum Mean Squared Error) equalization and assume perfect knowledge of the transmission channels.

A linear adaptive algorithm for data fusion in distributed detection systems

In this work we propose an adaptive fusion procedure to perform data detection in distributed detection systems with a decode-then-fuse type of receiver. Differently from previously proposed fusion rules, where nodes statistics (e.g. miss detection, false alarm and a priori probabilities) and channel transition probabilities are generally needed, the proposed non-assisted adaptive fusion algorithm adapts its coefficients and decision threshold based only on the received signals, so that time-varying or inhomogeneous distributed detection systems are well suited. Computer simulations show that the proposed adaptive fusion strategy delivers a performance very close to the optimal fusion rule.

Blind detection techniques for IEEE 802.15.4a communication system

This paper considers the ultra wideband multi-user communication system of the IEEE 802.15.4a-2007 standard. We propose a receiver scheme based on sampling at chip rate followed by a filter matched to the so-called effective user code. Two blind estimators for the effective code are proposed. The first one is a full rank estimator which is efficient and simple to implement and does not involve complex matrix operations as usually required in other blind estimators. The second estimator uses a reduced rank processing stage, which is based in two steps: interpolation and decimation. These steps are jointly designed to optimize the output signal to noise ratio (SNR) of the observed reduced rank signal. The proposed reduced rank processing is incorporated to the blind estimator to produce a reduced rank blind estimator. Numerical results show the validity of the proposed receiver and estimators in multiuser transmission environments.

Channel estimation and frequency domain equalization for IEEE 802.15.4a communication system

This paper considers the ultra wideband multi-user communication system of the IEEE 802.15.4a-2007 standard. We explore the block transmission, single carrier and zero padding like structure of the transmit symbol frame to implement a frequency domain receiver. Using the fact that user spreading codes are pseudo randomly chosen and varies on a symbol-by-symbol basis, a simple and efficient channel estimation algorithm that does not require complex matrix operations is also proposed. Numerical results show superior performance of the implemented receiver when compared to previously proposed schemes.

Frequency domain equalization space-time block-coded CDMA transmission system

In this work we propose a space-time block-coded (STBF) CDMA transmission system suitable for use with frequency domain equalization (FDE) algorithms. We illustrate the FDE by implementing the maximal ratio combining, the zero forcing and the minimum mean squared error single user detection algorithms. A diversity gain analysis is developed and some interesting results are pointed out. It is shown through computer simulations that the proposed transmission system exhibits good performance in terms of bit error rate when compared to previously proposed STBC CDMA transmission systems.

A constrained IQRD-RLS blind detection algorithm for CDMA transmission systems in multipath channels

In this paper we propose an inverse QR decomposition based recursive least squares algorithm (IQRD-RLS) for the linearly constrained minimum variance (LCMV) receiver for CDMA transmission systems. The proposed algorithm is numerically stable and it is suitable for implementation in systolic arrays or DSP vector architectures. It is shown through computer simulations that the proposed algorithm outperforms, in terms of bit error rate, previously proposed IQRD-RLS based blind detection algorithms.

A Blind Channel Estimation Algorithm for Space-Time Coded MC-CDMA Receivers

In this paper we proposed a linearly constrained minimum variance receiver for a space-time coded multicarrier (MC) CDMA system in frequency selective fading channels. It is shown that in the proposed receiver the channel can be blindly estimated as the eigenvector that corresponds to the maximum eigenvalue of an autocorrelation matrix, and then, efficient algorithms for subspace tracking can be used. Computer simulations shows that the proposed channel estimation algorithm achieves performance comparable to traditional algorithms with less computational cost.