We consider the problem of estimating the frame error rate (FER) of a given memoryless binary symmetric channel by observing the success or failure of transmitted packets. Whereas FER estimation is relatively straightforward if all observations correspond to packets with equal length, the problem becomes considerably more complex when this is not the case. We develop FER estimators when

transmissions of different lengths are observed, together with the Cramer-Rao Lower Bound (CRLB). Although the main focus is on Maximum Likelihood (ML) estimation, we also obtain low complexity schemes performing close to optimal in some scenarios. In a second stage, we consider the case in which FER estimation is performed at a node different from the receiver, and incorporate the impairment of unreliable observations by considering noisy ACK/NAK feedback links. The impact of unreliable feedback is analyzed by means of the corresponding CRLB. In this setting, the ML estimator is obtained by applying the Expectation-Maximization algorithm to jointly estimate the error probabilities of the data and feedback links. Simulation results illustrate the benefits of the proposed estimators.

%B IEEE Transactions on Wireless Communications
%V 16
%P 3661 - 3673
%8 06/2017
%G eng
%N 6
%R 10.1109/TWC.2017.2686845
%0 Conference Paper
%B IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP)
%D 2017
%T Time-domain channel estimation for wideband millimeter wave systems with hybrid architecture
%A Kiran Venugopal
%A Ahmed Alkhateeb
%A Robert W. Heath Jr.
%A Nuria González-Prelcic
%K compass
%K mmWave
%K myrada
%X Millimeter wave (mm Wave) systems will likely employ large antennas at both the transmitter and receiver for directional beamforming. Hybrid analog/digital MIMO architectures have been proposed previously for leveraging both array gain and multiplexing gain, while reducing the power consumption in analog-to-digital converters. Channel knowledge is needed to design the hybrid precoders/combiners, which is difficult to obtain due to the large antenna arrays and the frequency selective nature of the channel. In this paper, we propose a sparse recovery based time-domain channel estimation technique for hybrid architecture based frequency selective mmWave systems. The proposed compressed sensing channel estimation algorithm is shown to provide good estimation error performance, while requiring small training overhead. The simulation results show that using multiple RF chains at the receiver and the transmitter further reduces the training overhead.

%B IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP) %P 6193-6197 %8 03/2017 %G eng %0 Conference Paper %B Asilomar Conf. on Signals, Systems and Computers %D 2016 %T Frequency selective multiuser hybrid precoding for mmWave systems with imperfect channel knowledge %A Jose P. Gonzalez-Coma %A Nuria González-Prelcic %A Luis Castedo %A Robert W. Heath Jr. %K compass %K mmWave %B Asilomar Conf. on Signals, Systems and Computers %8 11/2016 %G eng %R 10.1109/ACSSC.2016.7869044 %0 Journal Article %J IEEE Trans. Wireless Communications %D 2016 %T Low complexity hybrid precoding strategies for millimeter wave communication systems %A Cristian Rusu %A Roi Méndez-Rial %A Nuria González-Prelcic %A Robert W. Heath Jr. %K compass %K mmWave %XMillimeter communication systems use large antenna arrays to provide good average received power and to take advantage of multi-stream MIMO communication. Unfortunately, due to power consumption in the analog front-end, it is impractical to perform beamforming and fully digital precoding at baseband. Hybrid precoding/combining architectures have been proposed to overcome this limitation. The hybrid structure splits the MIMO processing between the digital and analog domains, while keeping the performance close to that of the fully digital solution. In this paper, we introduce and analyze several algorithms that efficiently design hybrid precoders and combiners starting from the known optimum digital precoder/combiner, which can be computed when perfect channel state information is available. We propose several low complexity solutions which provide different trade-offs between performance and complexity. We show that the proposed iterative solutions perform better in terms of spectral efficiency and/or are faster than previous methods in the literature. All of them provide designs which perform close to the known optimal digital solution. Finally, we study the effects of quantizing the analog component of the hybrid design and show that even with coarse quantization, the average rate performance is good.

%B IEEE Trans. Wireless Communications %V 15 %P 8380 - 8393 %8 12/2016 %G eng %N 12 %R 10.1109/TWC.2016.2614495 %0 Journal Article %J IEEE J. Selected Topics in Signal Processing. Special issue on Signal Processing for Millimeter Wave Wireless Communications %D 2016 %T An overview of signal processing techniques for millimeter wave MIMO systems %A Robert W. Heath Jr. %A Nuria González-Prelcic %A Sundeep Rangan %A Wonil Roh %A Akbar M. Sayeed %K compass %K mmWave %XCommunication at millimeter wave (mmWave) frequencies is defining a new era of wireless communication. The mmWave band offers higher bandwidth communication channels versus those presently used in commercial wireless systems. The applications of mmWave are immense: wireless local and personal area networks in the unlicensed band, 5G cellular systems, not to mention vehicular area networks, ad hoc networks, and wearables. Signal processing is critical for enabling the next generation of mmWave communication. Due to the use of large antenna arrays at the transmitter and receiver, combined with radio frequency and mixed signal power constraints, new multiple-input multiple-output (MIMO) communication signal processing techniques are needed. Because of the wide bandwidths, low complexity transceiver algorithms become important. There are opportunities to exploit techniques like compressed sensing for channel estimation and beamforming. This article provides an overview of signal processing challenges in mmWave wireless systems, with an emphasis on those faced by using MIMO communication at higher carrier frequencies.

%B IEEE J. Selected Topics in Signal Processing. Special issue on Signal Processing for Millimeter Wave Wireless Communications %V 10 %P 436 - 453 %8 04/2016 %G eng %N 3 %R 10.1109/JSTSP.2016.2523924 %0 Journal Article %J Linear Algebra and its Applications %D 2016 %T Properties of real and complex ETFs and their application to the design of low coherence frames %A Cristian Rusu %A Nuria González-Prelcic %A Robert W. Heath Jr. %B Linear Algebra and its Applications %V 508 %P 81-90 %8 November, 2016 %G eng %U http://www.sciencedirect.com/science/article/pii/S0024379516302555 %0 Journal Article %J IEEE Trans. Communications %D 2016 %T Robust analog precoding designs for millimeter wave MIMO transceivers with frequency and time division duplexing %A Pengfei Xia %A Robert W. Heath Jr. %A Nuria González-Prelcic %K compass %K mmWave %XMillimeter wave (mmWave) communication provides high data rates thanks to large arrays at the transmitter and receiver, coupled with large bandwidth channels. Exploiting the arrays is challenging due to the need to configure precoding at the transmitter based on the large frequency selective channel. In this paper, we exploit the power iteration principle and propose a robust analog precoding training algorithm that can be applied in both frequency division duplex transmission systems and time division duplex transmission systems with or without RF calibration. We further analyze the convergence of the proposed algorithm and show how it converges to the singular value decomposition optimality exponentially. We propose null space projection on top of the power iteration to form multiple orthogonal beams at the transmitter and receiver. Strongest tap selection with proper energy pruning is used to collect as much precoding gain as possible from a frequency selective fading channel. The exponential effective SINR mapping performance is evaluated and demonstrates that the overall approach works smoothly. Numerical simulation results demonstrate algorithm robustness and the algorithm works not only for the simplified mmWave directional channels, but also for more general rich scattering channels.

%B IEEE Trans. Communications %V 64 %P 4622 - 4634 %8 11/2016 %G eng %N 11 %R 10.1109/TCOMM.2016.2604312 %0 Conference Paper %B IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP) %D 2015 %T An attack on antenna subset modulation for millimeter-wave communication %A Cristian Rusu %A Nuria González-Prelcic %A Robert W. Heath Jr. %K adversarial signal processing %K compass %K mmWave %XAntenna subset modulation (ASM) is a physical layer security technique that is well suited for millimeter wave communication systems. The key idea is to vary the radiation pattern at the symbol rate by selecting one from a subset of patterns with a similar main lobe and different side lobes. This paper shows that ASM is not robust to an eavesdropper that makes multiple simultaneous measurements at multiple angles. The measurements are combined and used to formulate an estimation problem to undo the effects of the side lobe randomization. Simulations show the performance of the estimation algorithms and how the eavesdropper can effectively recover the information if the signal-to-noise ratio exceeds a certain threshold. Using fewer active radio frequency chains makes it harder for the attacker to recover the transmit symbol, at the expense of more grating lobes.

%B IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP) %I IEEE %C Brisbane, Australia %P 2914-2918 %8 04/2015 %G eng %0 Conference Paper %B IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP) %D 2015 %T Augmented covariance estimation with a cyclic approach in DOA %A Roi Méndez-Rial %A Nuria González-Prelcic %A Robert W. Heath Jr. %K DOA estimation %K Non-uniformly spaced arrays %XHigh resolution direction-of-arrival (DOA) estimation is an important problem in many array signal processing applications. This paper proposes an augmented covariance estimator for DOA estimation. The new method exploits the periodicity of the covariance lags when the DOAs are assumed on a discrete grid with a certain resolution. Then, it achieves twice the resolution of typical methods such as the direct augmentable approach or forward backward spatial smoothing. When the sources are not on the discrete grid, an interpolated array manifold technique is proposed to mitigate the grid mismatch error.

%B IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP) %I IEEE %C Brisbane, Australia %P 2784-2788 %8 04/2015 %G eng %0 Conference Paper %B IEEE Int. Workshop on Signal Processing Advances in Wireless Communications (SPAWC) %D 2015 %T Dictionary-free Hybrid Precoders and Combiners for mmWave MIMO Systems %A Roi Méndez-Rial %A Cristian Rusu %A Nuria González-Prelcic %A Robert W. Heath Jr. %K compass %K mmWave %B IEEE Int. Workshop on Signal Processing Advances in Wireless Communications (SPAWC) %I IEEE %C Stockholm, Sweden %8 06/2015 %G eng %0 Conference Paper %B IEEE Int. Conference on Communications (ICC) %D 2015 %T Low Complexity Hybrid Sparse Precoding and Combining in Millimeter Wave MIMO Systems %A Cristian Rusu %A Roi Méndez-Rial %A Nuria González-Prelcic %A Robert W. Heath Jr. %K compass %K mmWave %B IEEE Int. Conference on Communications (ICC) %I IEEE %C London, UK %8 06/2015 %G eng %0 Conference Paper %B Asilomar Conf. on Signals, Systems and Computers %D 2014 %T Channel estimation in millimeter wave MIMO systems with one-bit quantization %A Jianhua Mo %A Phil Schniter %A Nuria González-Prelcic %A Robert W. Heath Jr. %K adaptive signal processing %K compass %K mmWave %B Asilomar Conf. on Signals, Systems and Computers %G eng %R 10.1109/ACSSC.2014.7094595 %0 Conference Paper %B ICASSP2014 - Signal Processing for Communications and Networking (ICASSP2014 - SPCOM) %D 2014 %T FER prediction with variable codeword length %A Alberto Rico-Alvariño %A Robert W. Heath Jr. %A Carlos Mosquera %K adaptive signal processing %K compass %K dynacs %K Effective SNR %K FER prediction %K PHY abstraction %XFrame error rate (FER) prediction in wireless communication systems is an important tool with applications to system level simulations and link adaptation, among others. Although in realistic communication scenarios it is expected to have codewords of different lengths, previous work on FER prediction marginally treated the dependency of the FER on the codeword length. In this paper, we present a method to estimate the FER using codewords of different length. We derive a low complexity FER estimator for frames of different length transmitted over a binary symmetric channel of unknown error probability. We extend this technique to coded systems by the use of effective SNR FER predictors. The proposed estimation scheme is shown to outperform other simpler estimation methods.

%B ICASSP2014 - Signal Processing for Communications and Networking (ICASSP2014 - SPCOM) %C Florence, Italy %G eng %R 10.1109/ICASSP.2014.6853935 %0 Journal Article %J IEEE Transactions on Wireless Communications %D 2014 %T Learning-Based Adaptive Transmission for Limited Feedback Multiuser MIMO-OFDM %A Alberto Rico-Alvariño %A Robert W. Heath Jr. %K adaptive signal processing %K dynacs %B IEEE Transactions on Wireless Communications %G eng %R 10.1109/TWC.2014.2314104 %0 Journal Article %J IEEE Communications Magazine %D 2014 %T MIMO precoding and combining solutions for millimeter wave systems %A Ahmed Alkhateeb %A Jianhua Mo %A Nuria González-Prelcic %A Robert W. Heath Jr. %K adaptive signal processing %K compass %K mmWave %XMillimeter-wave communication is one way to alleviate the spectrum gridlock at lower frequencies while simultaneously providing high-bandwidth communication channels. MmWave makes use of MIMO through large antenna arrays at both the base station and the mobile station to provide sufficient received signal power. This article explains how beamforming and precoding are different in MIMO mmWave systems than in their lower-frequency counterparts, due to different hardware constraints and channel characteristics. Two potential architectures are reviewed: hybrid analog/digital precoding/combining and combining with low-resolution analog- to-digital converters. The potential gains and design challenges for these strategies are discussed, and future research directions are highlighted.

%B IEEE Communications Magazine %V 52 %P 122-131 %8 12/2014 %G eng %N 12 %R 10.1109/MCOM.2014.6979963 %0 Conference Paper %B 21st European Signal Processing Conference 2013 (EUSIPCO 2013) %D 2013 %T Learning Based Link Adaptation in Multiuser MIMO-OFDM %A Alberto Rico-Alvariño %A Robert W. Heath Jr. %K dynacs %K link adaptation %K Machine Learning %K Multiuser MIMO-OFDM %XLink adaptation in multiple user multiple-input multiple-output orthogonal frequency division multiplexing communication systems is challenging because of the coupling between user selection, mode selection, precoding, and equalization. In this paper, we present a methodology to perform link adaptation under this multiuser setting, focusing on the capabilities of IEEE 802.11ac. We propose to use a machine learning classifier to solve the problem of selecting a proper modulation and coding scheme, combined with a greedy algorithm that performs user and spatial mode selection. We observe that our solution offers good performance in the case of perfect channel state information or high feedback rate, while those scenarios with less feedback suffer some degradation due to inter-user interference.

%B 21st European Signal Processing Conference 2013 (EUSIPCO 2013) %C Marrakech, Morocco %G eng %0 Conference Paper %B Asilomar Conference on Signals Systems and Computers %D 2013 %T Link Adaptation in MIMO-OFDM with Practical Impairments %A Alberto Rico-Alvariño %A Robert W. Heath Jr. %K dynacs %K link adaptation %K MIMO-OFDM %B Asilomar Conference on Signals Systems and Computers %G eng %R 10.1109/ACSSC.2013.6810579