Unai Fernández-Plazaola

Generalized BER Analysis of QAM and Its Application to MRC Under Imperfect CSI and Interference in Ricean Fading Channels

A general framework for the bit error rate (BER) analysis of quadrature amplitude modulation (QAM) systems is presented. This analysis is valid for any QAM system with independent bit mapping for in-phase and quadrature components and includes previous analyses in the literature as particular cases. We use this methodology to analyze BER in maximal ratio combining (MRC) systems with channel estimation errors in Ricean fading channels with Ricean-faded interference. An exact closed-form expression for the BER is obtained in this scenario, as well as an accurate simplified expression when perfect channel estimation is assumed, for the common case of Rayleigh-faded interference.

BER Analysis for Zero-Forcing SC-FDMA Over Nakagami-m Fading Channels

In this paper, we present an analytical study of the bit error rate (BER) for single-carrier frequency-division multiple access (SC-FDMA) transmission over frequency-selective fading channels when zero-forcing frequency-domain equalization is applied. SC-FDMA, which can be described as a precoded version of orthogonal frequency-division multiple access (OFDMA), is regarded as a promising candidate for next mobile communication systems due its favorable envelope characteristics and low peak-to-average-power ratio (PAPR), compared with that of OFDMA. We focus on Nakagami-m fading channels and provide a method to calculate BER values with a single numerical computation. We provide a closed-form expression for the BER with binary phase-shift keying (BPSK) and square M-ary quadrature amplitude modulation (M-QAM) under the assumption of independence among channel frequency responses for allocated subcarriers.

Exact BER analysis for M-QAM modulation with transmit beamforming under channel prediction errors

Significant throughput improvements can be obtained in multiple-input multiple-output (MIMO) fading channels by merging beamforming at the transmitter and maximal ratio combining (MRC) at the receiver. In general, accurate channel state information (CSI) is required to achieve these performance gains. In this paper, we analyze the impact of channel prediction error on the bit error rate (BER) of combined beamforming and MRC in slow Rayleigh fading channels. Exact closed-form BER expressions are obtained in terms of elementary functions. Numerical results show that imperfect CSI causes little BER degradation using channel prediction of moderate complexity.

Analysis of Adaptive MIMO Transmit Beamforming Under Channel Prediction Errors Based on Incomplete Lipschitz–Hankel Integrals

This paper provides new results for a family of incomplete Lipschitz-Hankel integrals (ILHIs) which also lead to the evaluation of certain integrals involving the generalized Marcum Q function. These mathematical results are then applied to analyze the bit error rate (BER) of adaptive modulation over multiple-input-multiple-output (MIMO) fading channels under imperfect channel state information (CSI). A novel exact closed-form expression for the average BER of adaptive modulation under MIMO transmit beamforming with maximal ratio combining, assuming prediction errors at the receiver for the adaptation CSI required by the transmitter, is obtained. The benefit of this result with respect to previous analysis is threefold. First, the expression is an exact closed form. Second, it is applicable to any antenna configuration, and third, it allows a design improvement of the cutoff SNR thresholds, which leads to better system performance in terms of average spectral efficiency at no extra cost.

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.

Spectral Efficiency of Interleaved SC-FDMA With Adaptive Modulation and Coding Over Nakagami-

Because it achieves similar performance to that of orthogonal frequency-division multiple access (OFDMA) with much more favorable envelope characteristics and lower peak-to-average power ratio (PAPR), single-carrier frequency-division multiple access (SC-FDMA) was chosen as the uplink transmission technology for Long Term Evolution (LTE) and LTE-Advanced systems. This choice has provoked a growing interest in this transmission technology; therefore, there is extensive literature on its performance in terms of bit error rate (BER) and PAPR. However, research on its spectral efficiency has been scarce until now. This paper aims to help fill this gap with an analytical study of the spectral efficiency in SC-FDMA when adaptive modulation and coding (AMC) and linear frequency-domain equalization are applied. This paper therefore computes the spectral efficiency for zero-forcing (ZF) and minimum-mean-square-error frequency-domain equalization (MMSE-FDE) for different Nakagami-m fading channels.

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The performance of multiple-input multiple-output (MIMO) systems using spatial multiplexing is analyzed under channel prediction errors. We derive exact closed-form expressions for the conditional and average bit error rate (BER) for both fixed and adaptive modulation. We apply our analysis to design a rate adaptation policy that optimally adapts antenna use between beamforming and spatial multiplexing. Our results indicate that the prediction error degrades BER in MIMO systems with spatial multiplexing much more than in MIMO systems with beamforming due to the self-interference that arises from channel coupling. In particular, if interference between eigenchannels is high, spatial multiplexing should not utilize the weakest eigenchannels. In our policy, beamforming is used when prediction error is high to avoid interference, whereas multiplexing is used when it is low to achieve the maximum multiplexing gain. We show that this policy improves performance over prior adaptive policies that have been proposed in the literature.

Fading Channels

The sum of ratios of two complex Gaussian random variables appears frequently in the mathematical analysis of telecommunication systems when zero-forcing equalization is applied. This paper is focused on the study of one of those systems: a simple Orthogonal Frequency Division Multiplexing (OFDM) relay network. The reason behind the election of this particular scenario is the recent interest on employing relay networks in wireless and mobile broadband systems to increase the coverage and throughput in a cost-effective way. Thus, the probability distribution of enhanced noise, made up by the sum of ratios of complex Gaussian random variables, is used to obtain a closed-form expression for the BER in the scenario under study.

Adaptive Modulation for MIMO Systems with Channel Prediction Errors

The design and validation of forthcoming mobile communication technologies (Beyond 3G and 4G) require appropriate tools for building reference models. In this article, a new tool called WM-SIM (Wireless Mobile SIMulator) is presented and compared with others recognized tools as Simulink, Visual System Simulator (VSS) and Ptolemy II. Benchmark results have proved WM-SIM to be more efficient than aforementioned tools in terms of processing time. Finally, results obtained with a model of the coming cellular Long Term Evolution (LTE) technology are presented in order to prove our platform as a good option to evaluate this kind of systems.

Sum of Ratios of Complex Gaussian RVs and Its Application to a Simple OFDM Relay Network

Important throughput improvements in multiple- input multiple-output (MIMO) fading channels can be obtained by merging beamforming at the transmitter and maximal ratio combining (MRC) at the receiver. However, to attain these performance gains it is important to obtain accurate channel state information (CSI). For this purpose a channel estimation technique is used at the receiver: channel prediction to feed back to the transmitter for beamforming, and channel interpolation for MRC at the receiver. In this paper, the impact of imperfect channel prediction on bit error probability (BEP) is analyzed in Rayleigh fading, taking into account the channel response variations over the frame interval. An exact closed-form expression for BEP is obtained, and we evaluate this expression assuming both time-variant and time-invariant channel models. These results indicate that the BEP performance degrades on the order of 1.5 dB due to channel variations.