arXiv subjects

David W. Matolak

Publications and source records attributed to David W. Matolak.

14 recordsLinked to original sources

arXiv2022

Wireless Connectivity and Localization for Advanced Air Mobility Services

By serving as an analog to traffic signal lights, communication signaling for drone to drone communications holds the key to the success of advanced air mobility (AAM) in both urban and rural settings. Deployment of AAM applications such as air taxis and air ambulances, especially at large-scale, requires a reliable channel for a point-to-point and broadcast communication between two or more aircraft. Achieving such high reliability, in a highly mobile environment, requires communication systems designed for agility and efficiency. This paper presents the foundations for establishing and maintaining a reliable communication channel among multiple aircraft in unique AAM settings. Subsequently, it presents concepts and results on wireless coverage and mobility for AAM services using cellular networks as a ground network infrastructure. Finally, we analyze the wireless localization performance at 3D AAM corridors when cellular networks are utilized, considering different corridor heights and base station densities. We highlight future research directions and open problems to improve wireless coverage and localization throughout the manuscript.

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arXiv2020

DFT-spread-OFDM Based Chirp Transmission

In this study, we propose a framework for chirp-based communications by exploiting discrete Fourier transform-spread orthogonal frequency division multiplexing (DFT-s-OFDM). We show that a well-designed frequency-domain spectral shaping (FDSS) filter for DFT-s-OFDM can convert its single-carrier nature to a linear combination of chirps circularly translated in the time domain. Also, by exploiting the properties of the Fourier series and Bessel function of the first kind, we analytically obtain the FDSS filter for an arbitrary chirp. We theoretically show that the chirps with low ripples in the frequency domain result in a lower bit-error ratio (BER) via less noise enhancement. We also address the noise enhancement by exploiting the repetitions in the frequency. The proposed framework offers a new way to efficiently synthesize chirps that can be used in Internet-of-Things (IoT), dual-function radar and communication (DFRC) or wireless sensing applications with existing DFT-s-OFDM transceivers.

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arXiv2020

Noncoherent Multiuser Chirp Spread Spectrum: Performance with Doppler and Asynchronism

In this paper, we investigate multi user chirp spread spectrum with noncoherent detection as a continuation of our work on coherent detection in [1]. We derive the analytical bit error ratio (BER) expression for binary chirp spread spectrum (BCSS) in the presence of multiple access interference (MAI) caused by correlation with other user signals because of either asynchronism or Doppler shifts, or both, and validate with simulations. To achieve this we analyze the signal cross correlations, and compare traditional linear chirps with our recently-proposed nonlinear chirps introduced in [1] and with other nonlinear chirps from the literature. In doing so we illustrate the superior performance of our new nonlinear chirp designs in these practical conditions, for the noncoherent counterpart of [1].

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arXiv2020

Nonlinear Quasi-Synchronous Multi User Chirp Spread Spectrum Signaling

Multi user orthogonal chirp spread spectrum (OCSS) can improve the spectral inefficiency of chirp spread spectrum (CSS) but is only feasible with perfect synchronism and without any channel dispersion. Asynchronism, channel dispersion, or unexpectedly large Doppler shifts can cause multiple access interference (MAI), which degrades performance. Conditions with small timing offsets we term quasi-synchronous (QS). In this paper, we propose two new sets of nonlinear chirps to improve CSS system performance in QS conditions. We analytically and numerically evaluate cross-correlation distributions. We also derive the bit error probability for Binary CSS analytically and validate our theoretical result with both numerical and simulation results; our error probability expression is applicable to any binary time-frequency (TF) chirp waveform. Finally, we show that in QS conditions our two new nonlinear chirp designs outperform the classical linear chirp and all existing nonlinear chirps from the literature. To complete our analysis, we demonstrate that our nonlinear CSS designs outperform existing chirps in two realistic (empirically modeled) dispersive air to ground channels.

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arXiv2020

EMR: A New Metric to Assess the Resilience of Directional mmWave Channels to Blockages

Millimeter-wave (mmWave) communication systems require narrow beams to increase communication range. If the dominant communication direction is blocked by an obstacle, an alternative and reliable spatial communication path should be quickly identified to maintain connectivity. In this paper, we introduce a new metric to quantify the effective multipath richness (EMR) of a directional communication channel by considering the strength and spatial diversity of the resolved paths, while also taking into account beamwidth and blockage characteristics. The metric is defined as a weighted sum of the number of multipath component (MPC) clusters, where clustering is performed based on the cosine-distance between the MPCs that have power above a certain threshold. This process returns a single scalar value for a transmitter (TX)/receiver (RX) location pair in a given environment. It is also possible to represent the EMR of the whole environment with a probability distribution function of the metric by considering a set of TX/RX locations. Using this proposed metric, one can assess the scattering richness of different communication environments to achieve a particular quality of service (QoS). This metric is especially informative and useful at higher frequencies, such as mmWave and terahertz (THz), where the propagation path loss and penetration loss are high, and directional non-light-of-sight (NLOS) communication is critical for the success of the network. We evaluate the proposed metric using our channel measurements at 28 GHz in a large indoor environment at a library setting for LOS and NLOS scenarios.

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arXiv2020

Advanced Physical-Layer Technologies in VHF Data Link Communications

Due to the rapidly increasing number of flights and high usage of VHF channels, the VHF spectrum is becoming much more crowded, and use of analog waveforms will likely not maintain the required performance. Therefore, digital communications have been considered due to larger spectral efficiency. Notably, VHF data link modes 2 and 3 (VDL2 and 3) using D8PSK modulation has been proposed. VDL2 and 3 received attention due to its simplicity and more constant amplitude waveform, yielding lower PAPR. Recently, advanced VHF digital link (A-VDL) was proposed for VHF. This scheme enables use of essentially the same platform as VDL except for the physical layer processing, including modulation. The proposed A-VDL, following DVB-S2 standard, uses APSK modulation with higher modulation order than VDL, hence providing higher spectral efficiency than VDL. Compared to the widely used QAM, APSK is more resistant to amplifier amplitude and phase distortions. Thus, APSK has become of interest for satellite communications, as well as VHF communications in A-VDL. In this paper, we investigate other advanced technologies such as channel encoding technique low-density parity-check (LDPC), more efficient standardized voice encoders, as well as better pulse shaping filters than the classical square-root raised-cosine filter used in VDL and A-VDL. Via simulations and analysis, we compare the proposed scheme's link margin, PAPR, and spectral efficiency compared to VDL and A-VDL, which both use Reed Solomon (RS) encoding. In addition, as another way of generating the same VDL waveforms (or possibly other single-carrier aeronautical band waveforms), we investigate the single-carrier type waveform used in cellular LTE and 5G uplink communication links, the discrete Fourier transform-spread OFDM (DFT-s-OFDM), and discuss how we can take advantage of using the same LTE and 5G hardware resources.

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arXiv2020

Multicarrier Spectral Shaping for Non-White Interference Channels: Application to L-band Aviation Channels

In this paper, we investigate an algorithm to attain additive white Gaussian noise (AWGN) performance in spectrally non-white channels, using multicarrier communications, i.e., orthogonal frequency division multiplexing (OFDM) and filterbank multicarrier (FBMC). The non-white channel can be from non-white noise, or more commonly, interference. Our algorithm uses a simple optimization method to find usable subcarriers and assigns different power levels to the subcarriers to attain the equivalent AWGN channel bit error ratio (BER). Subcarriers that experience very high interference are assigned as null subcarriers. After describing our analysis, we show results for two non-white interference signal examples: the Gaussian pulse shaped distance measuring equipment (DME) pulses, and a classical rectangular-pulse interference signal. The DME example is pertinent for currently proposed aviation communication systems, where new multicarrier techniques, e.g., the L-band digital aviation communication systems (LDACS) have been designed as an inlay approach between the high-power DME channels in the L-band. Our results show how using this adaptive technique can improve performance and spectral efficiency, whereas fixed bandwidth schemes such as LDACS could suffer significant performance degradation. These results show the utility of this idea for future adaptive and cognitive radio applications for aviation or other non-white channels.

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arXiv2020

Attenuation of Several Common Building Materials in Millimeter-Wave Frequency Bands: 28, 73 and 91 GHz

Future cellular systems will make use of millimeter wave (mmWave) frequency bands. Many users in these bands are located indoors, i.e., inside buildings, homes, and offices. Typical building material attenuations in these high frequency ranges are of interest for link budget calculations. In this paper, we report on a collaborative measurement campaign to find the attenuation of several typical building materials in three potential mmWave bands (28, 73, 91 GHz). Using directional antennas, we took multiple measurements at multiple locations using narrow-band and wide-band signals, and averaged out residual small-scale fading effects. Materials include clear glass, drywall (plasterboard), plywood, acoustic ceiling tile, and cinder blocks. Specific attenuations range from approximately 0.5 dB/cm for ceiling tile at 28 GHz to approximately 19 dB/cm for clear glass at 91 GHz.

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arXiv2020

UAV Command and Control, Navigation and Surveillance: A Review of Potential 5G and Satellite Systems

Drones, unmanned aerial vehicles (UAVs), or unmanned aerial systems (UAS) are expected to be an important component of 5G/beyond 5G (B5G) communications. This includes their use within cellular architectures (5G UAVs), in which they can facilitate both wireless broadcast and point-to-point transmissions, usually using small UAS (sUAS). Allowing UAS to operate within airspace along with commercial, cargo, and other piloted aircraft will likely require dedicated and protected aviation spectrum at least in the near term, while regulatory authorities adapt to their use. The command and control (C2), or control and non-payload communications (CNPC) link provides safety critical information for the control of the UAV both in terrestrial-based line of sight (LOS) conditions and in satellite communication links for so-called beyond LOS (BLOS) conditions. In this paper, we provide an overview of these CNPC links as they may be used in 5G and satellite systems by describing basic concepts and challenges. We review new entrant technologies that might be used for UAV C2 as well as for payload communication, such as millimeter wave (mmWave) systems, and also review navigation and surveillance challenges. A brief discussion of UAV-to-UAV communication and hardware issues are also provided.

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arXiv2020

Chirp Spread Spectrum Signaling for Future Air-Ground Communications

In this paper, we investigate the use of chirp spread spectrum signaling over air-ground channels. This includes evaluation of not only the traditional linear chirp, but also of a new chirp signal format we have devised for multiple access applications. This new format is more practical than prior multi-user chirp systems in the literature, because we allow for imperfect synchronism. Specifically we evaluate multi-user chirp signaling over air-ground channels in a quasi-synchronous condition. The air-ground channels we employ are models based upon an extensive NASA measurement campaign. We show that our new signaling scheme outperforms the classic linear chirp in these air-ground settings.

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arXiv2020

Golay Layer: Limiting Peak-to-Average Power Ratio for OFDM-based Autoencoders

In this study, we propose a differentiable layer for OFDM-based autoencoders (OFDM-AEs) to avoid high instantaneous power without regularizing the cost function used during the training. The proposed approach relies on the manipulation of the parameters of a set of functions that yield complementary sequences (CSs) through a deep neural network (DNN). We guarantee the peak-to-average-power ratio (PAPR) of each OFDM-AE symbol to be less than or equal to 3 dB. We also show how to normalize the mean power by using the functions in addition to PAPR. The introduced layer admits auxiliary parameters that allow one to control the amplitude and phase deviations in the frequency domain. Numerical results show that DNNs at the transmitter and receiver can achieve reliable communications under this protection layer at the expense of complexity.

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arXiv2019

PAPR Analysis for Dual-Polarization FBMC

In a recent work we proposed a new radio access technique based on filter bank multi-carrier (FBMC) modulation using two orthogonal polarizations: dual-polarization FBMC (DP-FBMC). We showed that with good cross-polarization discrimination (XPD), DP-FBMC solves the intrinsic imaginary interference shortcoming of FBMC without extra processing. DP-FBMC also has other interesting advantages over cyclic prefix orthogonal frequency-division multiplexing (CP-OFDM) and FBMC such as more robustness in dispersive channels, and it is also more robust to receiver carrier frequency offset (CFO) and timing offset (TO). In this paper we analyze the peak to average power ratio (PAPR) of DP-FBMC and compare PAPR simulation results with that of conventional FBMC, for different prototype filters and overlapping factors. According to the analysis and results, with a proper choice of prototype filter, DP-FBMC has comparable PAPR to FBMC.

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arXiv2018

Dual-Polarization FBMC for Improved Performance in Wireless Communication Systems

Filter bank multi-carrier (FBMC) offers superior spectral properties compared to cyclic-prefix orthogonal frequency-division multiplexing (CP-OFDM), at the cost of an inherent shortcoming in dispersive channels called intrinsic imaginary interference. In this paper we propose a new FBMC based communication system using two orthogonal polarizations for wireless communication systems: dual-polarization FBMC (DP-FBMC). Using this system we can significantly suppress the FBMC intrinsic interference. Therefore in DP-FBMC all the multicarrier techniques used in CP-OFDM systems such as channel equalization, etc., should be applicable without using the complex processing methods required for conventional FBMC. DP-FBMC also has other interesting advantages over CP-OFDM and FBMC: it is more robust in highly dispersive channels, and also to receiver carrier frequency offset (CFO) and timing offset (TO). In our DP-FBMC system we propose three different structures based on different multiplexing techniques. We show that compared to conventional FBMC, one of these DP-FBMC structures has equivalent complexity and equipment requirements. We compare DP-FBMC with other systems through simulations. According to our results DP-FBMC has potential as a promising candidate for future wireless communication networks.

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arXiv2018

Dual-Polarization OFDM-OQAM Wireless Communication System

In this paper we describe the overall idea and results of a recently proposed radio access technique based on filter bank multicarrier (FBMC) communication system using two orthogonal polarizations: dual-polarization FBMC (DP-FBMC). Using this system we can alleviate the intrinsic interference problem in FBMC systems. This enables use of all the multicarrier techniques used in cyclic-prefix orthogonal frequency-division multiplexing (CP-OFDM) systems for channel equalization, multiple-input/multiple-output (MIMO) processing, etc., without using the extra processing required for conventional FBMC. DP-FBMC also provides other interesting advantages over CP-OFDM and FBMC such as more robustness in multipath fading channels, and more robustness to receiver carrier frequency offset (CFO) and timing offset (TO). For DP-FBMC we propose three different structures based on different multiplexing techniques in time, frequency, and polarization. We will show that one of these structures has exactly the same system complexity and equipment as conventional FBMC. In our simulation results DP-FBMC has better bit error ratio (BER) performance in dispersive channels. Based on these results, DP-FBMC has potential as a promising candidate for future wireless communication systems.

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