F. J. Lopez-Martinez

Higher Order Statistics of Sampled Fading Channels With Applications

In this paper, we present a novel analytical framework for the calculation of the level crossing rate (LCR) and the average fade duration (AFD) of fading channels sampled at a certain sampling period TS. These expressions are valid for arbitrary fading distributions with arbitrary correlation and can be easily computed in terms of the cumulative distribution function (cdf) of the fading envelope and its bivariate cdf. This approach yields interesting insights into the effect of finite sampling in the higher order statistics of fading processes. We also demonstrate that the proposed expressions for sampled fading process converge with the existing expressions for continuous fading processes as the sampling period tends to zero. As a direct application, exact closed-form expressions are given for the LCR and AFD of sampled Rayleigh fading processes, which are suitable to characterize the higher order statistics of the equivalent frequency-domain fading process in multipath Rayleigh fading.

Exact Closed-Form BER Analysis of OFDM Systems in the Presence of IQ Imbalances and ICSI

In this paper, we derive an exact closed-form expression for the bit error rate (BER) of orthogonal frequency division multiplexing (OFDM) systems impaired by transmit (TX) and receive (RX) in-phase/quadrature (IQ) imbalances and imperfect channel state information (ICSI), in Rayleigh fading channels. Since the decision metric in this scenario can be expressed as a quadratic form D in Gaussian complex-valued non-circularly symmetric random variables (RVs) with zero mean, we provide a general expression for the calculation of Pr{D <; 0}. In addition, two approximate closed-form expressions for the BER are obtained, which are demonstrated to be extremely accurate for practical values of IQ imbalances. Results show that TX IQ imbalance is in general less detrimental than RX IQ imbalance, and confirm that the correlation between the channel response at the observed subcarrier frequency and the mirror subcarrier has a significant impact in the BER.

Further Improvements in SOVA for High-Throughput Parallel Turbo Decoding

In this letter, we present two mechanisms based on soft-output Viterbi algorithm (SOVA) technique that achieve a performance close to maximum a posteriori (MAP) decoding. First, we propose a new technique called alternating direction SOVA, which allows for improving the performance of SOVA in similar terms as bidirectional SOVA while barely affecting the area complexity. Then, we introduce the idea of parallel turbo decoding based on path metric/state border exchange. Unlike other techniques, overlapping between adjacent subblocks is not required, thus reducing the decoding latency dramatically. We evaluate their performance in the context of 3GPP-LTE, showing that the combination of both mechanisms achieves a BER performance close to parallel MAP decoding while having a lower complexity.

Low Complexity Synchronization and Frequency Equalization for OFDM Systems

This paper shows an efficient implementation of symbol synchronization and frequency equalization algorithms for OFDM (orthogonal frequency division multiplexing) based systems. The aim is to have a low complexity realization that can be implemented on a FPGA (Field Programmable Gate Array), to obtain an area-efficient receiver. The algorithms are described theoretically, and hardware considerations about their implementation are discussed. Furthermore, the proposed methods have been tested on a real-time FPGA platform.

Joint Time, Frequency and Sampling Clock Synchronization for OFDM-Based Systems

A blind method for jointly estimating and correcting time, carrier frequency and sampling clock frequency synchronization in OFDM based systems is proposed. The algorithm is particularlly suitable for low-cost terminal implementations, since it provides a great efficiency in terms of hardware complexity. Its performance has been tested on a real system, taking 3GPPLTE as target technology and FPGAs as hardware platform. Results show its good performance while keeping computational complexity unincreased.

On the Connection between Gaussian Q-Functions and a Class of Hypergeometric Functions: Application to LCR of Lognormal Processes

In this letter, we derive a closed-form expression for the two-dimensional joint Gaussian Q-function in terms of a class of hypergeometric functions. Particularly, we show that the 2-D Gaussian Q-function can be expressed in terms of the bivariate confluent hypergeometric function Φ1, which is well studied in classical books of integrals, special functions and Laplace transforms. As a direct application, we derive a new closed-form expression for the level crossing rate (LCR) and the average fade duration (AFD) of sampled lognormal processes with arbitrary correlation profile.

Design and FPGA implementation of an OFDMA baseband modem for 3GPP-LTE physical layer

This paper presents a FPGA implementation of an OFDMA modem for the physical layer of LTE technology, suitable for both uplink and downlink transmission. The designed structure achieves a low area occupation while fulfilling LTE requirements.

Hardware Implementation of a Correlation-based Synchronization Algorithm for Wireless OFDM

In the world of wireless communications, OFDM is one of the most used multicarrier techniques today. The main reasons for that are the multipath immunity that provides and the easy implementation of FFT, but OFDM systems are sensitive to timing synchronization errors. This paper shows a novel synchronization algorithm for the IEEE 802.16-2004 standard. The proposed method performs frame detection and determines the beginning of the data frame, by using a combination of auto and cross correlation techniques. Besides, a FPGA implementation of the developed algorithm is achieved in order to evaluate its performance on a real system.

Moment-Based Parameter Estimation for the Two-Wave with Diffuse Power Fading Model

In this paper, the estimation of the parameters of the Two- Wave with Diffuse Power (TWDP) fading distribution from the observation of the received signal envelope is addressed. Specifically, a moment-based approach for the estimation of the parameters K and &#916; for this fading model is introduced. We first set the boundaries of the estimation problem by calculating the Cramer-Rao lower Bound (CRB). Then, closed-from expressions that relate the moments of the received signal envelope to the parameters K and &#916; are used for the estimation. Monte-Carlo simulations show that the estimation error is close to the CRB for a wide range of values of the parameters K and &#916;.