Vehicle to Infrastructure (V2I) communication, an important part of intelligent transportation systems (ITS), can improve security and traffic efficiency through wireless connections in terrestrial automotive settings. We conducted V2I measurements in an urban environment. The measurements were performed using a 40 MHz bandwidth chirp signal at 5240 MHz center frequency. In our measurements, the transmitter (Tx) was stationary and the receiver (Rx), placed in a car, was driven along a street: both toward and away from the ground station (GS). We quantified the spatial power delay profile correlation coefficient (SPCC) and stationarity distance (SD) for this mixed environment (line-of-sight, non-line-of-sight, and partially obstructed). The average SD is between 3 m and 10 m, and the distribution of SD is approximately exponential. We also observed variation in SPCC and SD according to the asymmetry of the urban environment around the ground station.

A large amount of spectrum, enabling multi-Gigabits-per-second data rates, is offered by millimeter wave (mmWave) communication systems. Yet mmWave communication systems incur significant propagation challenges, including large free space path loss (PL), large penetration loss, and large diffraction loss. Hence, it is vital to quantify these and other channel effects to ensure link reliability, particularly in non-line-of-sight (NLOS) settings. As with many industries, commercial aviation is experiencing growth that could benefit from mmWave communication systems. In this paper, we present 90-GHz band measurement results for two aviation settings: an airport maintenance hangar and an airport baggage claim area. We address line-of-sight (LOS), NLOS, mixed LOS/NLOS, and LOS-to-NLOS transition settings. We provide results on path loss, delay spread, angle-of-arrival (AoA), and spatial stationarity distance. The highly-reflective maintenance hangar setting yields large AoA values (>104°). The minimum stationarity distance for both LOS and NLOS settings in the maintenance hangar is less than or equal to 0.5 m. Our PL exponent is close to the free space PL exponent, as expected in this baggage area open setting. A relatively large root mean square delay spread was observed in both LOS and NLOS baggage claim settings: 20.5 ns for LOS and 24 ns for NLOS.

Millimeter wave (mmWave) communication systems can offer unprecedented amounts of spectrum and multi-Gigabit-per-second (Gbps) data rates. Directional antennas are typically used to ensure adequate link range, and in non-line-of-sight (NLOS) regions, transceivers must often "search" in the angular domain for a signal of significant strength. This paper presents millimeter-wave propagation measurement results for both outdoor and indoor office scenarios at 90 GHz, focusing on LOS-to-NLOS transitions. Our results are based upon measurements using a 500-MHz bandwidth chirp signal. We first estimate propagation path loss, and model this using a single-frequency close-in (CI) free space reference distance model. Pathloss exponents are less than that for free space path: 1.6 for outdoor and 1.8 for indoors. The channel transitions can present some of the most challenging conditions to link reliability: large ranges and rapid rates of change of the strongest multipath component angle of arrival (AoA), root mean-square delay spread, and stationarity distance. We found abrupt path loss changes of over 13 dB for indoor and 17 dB for outdoor scenarios, and abrupt changes of the strongest-component AoA of up to 60 degrees over receiver travel distances of a few cm.

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.

In this paper, we investigate multi user chirp spread spectrum with noncoherent detection as a continuation of our work on coherent detection. 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 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.

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.

In this article, we propose a novel 3-D geometry-based stochastic model (GBSM), i.e., a two-cylinder model, for unmanned aerial vehicle (UAV) multiple-input-multiple-output (MIMO) Ricean fading channels. The received signal is a sum of the Line-of-Sight (LoS) component, single-bounced (SB) rays at the UAV side, SB rays at the ground station side, SB rays on the ground, and double-bounced rays. This makes our model adaptable to a wide variety of UAV communication scenarios. More importantly, the proposed UAV model is the first two-cylinder model that considers ground reflections. Moreover, our model has the ability to investigate the impact of some unique UAV-related parameters (e.g., the UAV's moving direction, UAV's altitude, and antenna orientation) on channel characteristics in a 3-D nonisotropic propagation environment. From the proposed model, we derive and study some significant statistical properties, including the space-time correlation function (CF), Doppler power spectral density (PSD), envelope level crossing rate (LCR), and average fade duration (AFD). Some numerical results and interesting observations are provided, which can be considered useful guidance for the design of UAV-MIMO communication systems. Finally, the utility of our model is verified by the close agreement between the theoretical results and some example measurement data.

In this paper, we present millimeter-wave (mmWave) penetration loss measurements and analysis at E- bands-73 GHz and 81 GHz. Penetration loss was measured for common building materials such as clear glass, metal, tinted glass, wood, and drywall on the campus of Boise State University in the city of Boise. A horn antenna with a gain of 24 dBi was used at the transmitter and receiver at both bands, and both antennas were boresight-aligned with respect to the test material. A total of twelve locations were selected to test five materials. We tested two indoor materials (clear glass and wood) in at least two locations to determine the effect of penetration loss of materials in similar compositions. The average penetration loss and standard deviation were estimated for these indoor materials. We measured an average penetration loss of 2 to 9 dB for wood and glass, respectively. Furthermore, we measured the penetration loss of common indoor and outdoor building materials. We studied that outdoor materials had larger penetration losses, e.g., we obtained a penetration loss of 22.69 dB for outdoor metal, where this value dropped to 16.04 dB for indoor metal at 73 GHz. Similar results were also obtained for the 81 GHz channel, where the largest penetration loss was measured to be 26.5 dB through a tinted glass door in an outdoor setting.

In this paper, two large-scale fading path loss models are presented based on indoor and outdoor channel measurements at 73 GHz. The line-of-sight millimeter-wave propagation measurement campaigns were uniquely conducted within the indoor and outdoor environments at an airport setting, i.e., the Boise Airport. The channel measurements were made with directional transmit and receive antennas with a 24 dBi gain at different receive antenna heights. From the measured data, we obtained the parameters of two path loss models, i.e., the close-in reference distance model (CIM) and the floating-intercept model (FIM). Results show that the path loss exponents estimated from the CIM are very close to that of the free- space path loss model, while the FIM provides a better fit to the measurement data.

Millimeter-wave links, which will be applied in 5G wireless communication, can suffer severe attenuation and multipath fading in indoor channels. Accurate indoor channel modeling for path loss is hence important. In this paper we address this for frequencies of 5, 31 and 90 GHz. An indoor environment is modeled and simulated via the X3D ray-tracing method in Wireless Insite® software, and results are post-processed in MATLAB. Measurements at each frequency were also made in the indoor environments for link distances up to 50 m. Two types of widely-used log-distance path loss models are used for comparing results: the close-in (CI) free-space reference model and the floating intercept (FI) model. Path loss simulation results are compared with measurement for different frequencies, antennas, and channel conditions. Our results show that CI model slopes between ray-tracing and measurements differ by less than 0.3, and model standard deviations differ by less than 2 dB for all frequencies for the line of sight (LOS) case. For a non-light-of-sight (NLOS) channel, differences are less than 0.6 for slope and 5 dB for standard deviations, illustrating the utility of ray-tracing for these frequencies and settings.

Powered by the Internet of Things, the vehicular ad-hoc networks are expected to evolve into the Internet of Intelligent Vehicles in which each vehicle can be much more efficient in various vehicular and transportation applications. In order to realize this vision, a seamless low-latency and ultrareliable vehicle-to-vehicle (V2V) communication network is required. Thus, it is of importance to characterize the V2V channels in various realistic environments, especially when the line-of-sight between transmitter (Tx) and receiver (Rx) is obstructed. In this paper, we characterize obstructed V2V channels in the 5-GHz band through measurement-calibrated ray-tracing (RT) simulations. To begin, the main objects in the real world are divided into two groups: 1) the small-scale structures (e.g., lampposts, traffic signs, etc.) and 2) the large-scale structures (such as buildings and ground). Then, we integrate the radar cross sections of the small-scale structures into our RT simulator through a framework based on high frequency prediction techniques. For the large-scale structures, we calibrate the electromagnetic and scattering parameters of the large-scale structures through V2V channel measurements. After such integration and calibration, extensive RT simulations for V2V channels with Tx and Rx located on vehicles traveling in the opposite or same direction are realized with various antenna deployments in urban and open space environments, with and without sloped terrain. Based on the RT results, we characterize the path loss, shadow fading, and delay spread of the channel for each case, and show agreement with measured results in the literature for all these channel characteristics.

Non-stationary channel models play a crucial role in today's communication systems. Mobile-to-mobile channels are known to exhibit non-stationary behavior caused by the movement of transmitter and receiver. Non-stationarity can be addressed by introducing time-variant stochastic functions such as the time-variant instantaneous Doppler probability density function or time-variant instantaneous characteristic function. An algebraic analysis of the time-variant Doppler probability density function (pdf) in a classical Cartesian coordinate system is only numerically tractable due to trigonometric functions in the resulting expressions. In contrast, it has been shown that by using prolate spheroidal coordinates for 2D vehicle-to-vehicle channels the algebraic analysis becomes analytically tractable. In this paper, the analysis is extended to air-to-air channels. It is shown that the time-variant Doppler pdf can be represented without trigonometric functions. The description of the Doppler frequency in prolate spheroidal coordinates allows describing it as an algebraic curve. This permits the use of algebraic methods to analyze the Doppler frequency and derive the boundaries of the resulting Doppler pdf. Using the developed tools, we have investigated exemplary air-to-air scenarios. However, the methodology can be extended to any air-to-air configuration.

There is an increase in usage of smaller cells or femtocells to improve performance and coverage of next-generation heterogeneous wireless networks (HetNets). However, the interference caused by femtocells to neighboring cells is a limiting performance factor in dense HetNets. This interference is being managed via distributed resource allocation methods. However, as the density of the network increases so does the complexity of such resource allocation methods. Yet, unplanned deployment of femtocells requires an adaptable and self-organizing algorithm to make HetNets viable. As such, we propose to use a machine learning approach based on Q-learning to solve the resource allocation problem in such complex networks. By defining each base station as an agent, a cellular network is modeled as a multi-agent network. Subsequently, cooperative Q-learning can be applied as an efficient approach to manage the resources of a multi-agent network. Furthermore, the proposed approach considers the quality of service (QoS) for each user and fairness in the network. In comparison with prior work, the proposed approach can bring more than a four-fold increase in the number of supported femtocells while using cooperative Q-learning to reduce resource allocation overhead.

Antenna selection (AS) is considered as an ideal approach for improving the performance of vehicle-to-vehicle (V2V) communications, while satisfying the hardware and power limitations that exist in vehicles. However, the promised gain over single antenna schemes is affected by the fast varying wireless channel, since AS is frequently performed using outdated versions of the signal-to-noise ratio. In this paper, we propose an AS scheme that exploits the stationarity of large scale fading. In particular, by adopting shadowing information as an AS criterion, the negative consequences of the outdated channel state information (CSI) can be alleviated, since large-scale fading varies more slowly as compared to small-scale fading. The performance of the proposed technique is analyzed using the criterion of outage probability. It is shown that the new scheme outperforms the corresponding one that is based on outdated CSI, especially in scenarios with mild channel conditions, in terms of fading/shadowing severity. Moreover, empirical results have been used to verify the effectiveness of the considered shadowing model.

Dense deployment of small base stations (SBSs) is one of the main methods to meet the 5G data rate requirements. However, high density of independent SBSs will increase the interference within the network. To circumvent this interference, there is a need to develop self-organizing methods to manage the resources of the network. In this paper, we present a distributed power allocation algorithm based on multi-agent Q-learning in an interference-limited network. The proposed method leverages coordination through simple message passing between SBSs to achieve an optimal joint power allocation. Simulation results show the optimality of the proposed method for a two-user case.

Millimeter wave (mmWave) communications can provide high speed data rate for 5G wireless networks, taking advantage of the large bandwidth available at mmWave frequencies. It is also well known that mmWave links may suffer from outages due to non-line-of-sight (NLOS) propagation problems. In this paper, we study the characteristics of IEEE~802.11ad based mmWave systems at 60~GHz, and investigate the effect of passive reflectors for improving coverage. The experiments are performed using Tensorcom single chip TC60G-USB3-EVB and TC60G70100UP picocell platforms in different indoor and outdoor environments, both supporting beamforming based on IEEE~802.11ad specifications. Our results show that the passive metallic reflectors may signifciantly improve the mmWave signal coverage in regions where the line-of-sight (LOS) connectivity between the transmitter and the receiver is limited.

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.

Aviation traffic is on the rise, in part due to a large increase in the number of unmanned aerial systems (UAS), also known as unmanned aerial vehicles (UAVs). With the rise in vehicle traffic will come increased communication traffic, and for the air-ground communications to/from all these air vehicles, new communication systems are required. In this paper we evaluate via simulations the performance of two new candidate systems over empirical air-ground channel models. These channel models - here for the 5 GHz band - are based on an extensive measurement campaign sponsored by NASA, with ground sites in multiple local environments. The two new multicarrier candidate schemes are 5 MHz bandwidth systems: a cyclic-prefix OFDM scheme similar to the previously proposed L-DACS1 scheme, and a new filterbank multicarrier (FBMC) scheme related to a prior L-band FBMC design of the authors. By taking advantage of the more compact FBMC spectrum, we can improve spectral efficiency via replacement of band-edge guard subcarriers with data-bearing subcarriers. Our design increases throughput by approximately 23%. The (uncoded) bit error ratio performance of the two schemes is evaluated for several modulations over three specific air-ground channels, and performance results are very similar between the two schemes: even in the worst-case channels and with highest modulation order, the FBMC bit error ratio is only marginally larger than that of the CP-OFDM scheme. Hence with nearly identical performance and significantly better throughput, the FBMC design is an attractive candidate for future air-ground communications in these settings.

The correlation between signals received on multiple antennas is a function of the channel(s) between them, and analysis of this is useful for spatial diversity and spatial multiplexing. In this paper we compute the correlations in both the spatial and frequency domains for a classical two-ray channel in a SIMO setting for an air-ground setting. We analyze this for the “pure” (deterministic) two-ray case, and also include results for the case where the two-ray channel incurs Ricean fading. After describing the setting and basic analysis, we show corroborating NASA measurement results for an air-ground over-sea channel. We show that both the spatial and frequency domain correlations are numerically computable, oscillatory functions, dependent upon link geometric parameters (antenna heights and link distance), surface electrical parameters, and frequency. With knowledge of these parameters, one can in principle select antenna separation and/or frequency separation to achieve diversity in settings where this classical channel model applies. This can be beneficial when narrowbeam (tracking) antennas that suppress the surface reflection are impractical to deploy.

Demands for very reliable and robust communications systems are becoming commonplace, and this is true for air-to-ground (AG) systems, which are seeing increased usage, particularly for unmanned aircraft. Available spectrum exists for AG communications systems in the L-band (960-1164 MHz). Two robust L-Band Digital Aeronautical Communication Systems (L-DACS) were recently defined, LDACS1 and LDACS2. The L-DACS1 scheme employs a fairly broadband (0.5 MHz) transmission using Cyclic-Prefix Orthogonal Frequency-Division Multiplexing (CP-OFDM) together with adaptive coding and modulation. In this paper we propose a new AG communication system based on OFDM-OQAM filter bank modulation, using features similar to those of the L-DACS1 physical layer, and show how better subcarrier filtering can improve spectrum efficiency in AG channels. Channel estimation (CE) in OFDM-OQAM systems must employ a pilot method completely different from classical pilot-based CP-OFDM systems, since in OFDM-OQAM the pilots should remove pilot subcarrier interference from neighboring subcarriers. We employ a low complexity pilot-based CE on the OFDM-OQAM signal, and show BER results for L-DACS1 and for comparable OFDM-OQAM based systems in an example AG channel. The AG channel we employ is one based upon a recent extensive measurement campaign. We also estimate channel throughput and mean square error (MSE) for these two systems, and show that for similar BER performance, both channel estimation and throughput of the new system are better than that for L-DACS1.

Unmanned aerial vehicles (UAVs) are expected to be used extensively in the near future in applications such as aerial surveillance, transportation, and disaster assistance. The conditions under which UAVs operate are different from those of conventional piloted aircrafts. This necessitates development of new air-to-ground (AG) propagation channel models for UAVs. To our best knowledge, there are limited studies in the literature on sounding and modeling of ultrawideband (UWB) AG propagation channels. In this work, comprehensive UWB measurements are conducted for various UAV communication scenarios using Time Domain P410 UWB kits. Both time and frequency domain analysis of the measured data are carried out. Based on the measured data, stochastic path loss and multipath channel models are developed to characterize AG UWB propagation channels.

The use of aeronautical vehicles and consequently their communication traffic are growing rapidly, and soon there will be demands for channels with larger bandwidths. The L-band digital aeronautical communication system (L-DACS1) was proposed by EUROCONTROL as an OFDM based multicarrier communication system candidate, with channels "inlayed" between distance measuring equipment (DME) channels. We previously proposed a similar communication system based on the Filter Bank Multicarrier (FBMC) technique, which has some significant advantages over L-DACS1. In this paper several diversity and multiple antenna techniques for L-DACS1 and FBMC AG communication systems are investigated. The correlation coefficient between realistic receiver aircraft antenna channels is computed, and using these realistic channels-based upon NASA channel measurements-link performance is simulated to generate BER results. Simulation results show the advantages of using multiple antennas at the receiver, and the antenna separations required (as a function of link distance) to attain nearly uncorrelated channels for two suburban areas. MIMO performance gains are quantified and show significant improvement over single-antenna systems, especially for higher order modulations.

The recent hot research topic of a massive multiple-output (MIMO) has been primarily studied based on the assumption that channel vectors are asymptotically pairwise orthogonal. This condition is not exactly satisfied in practice. Correlation will occur among antenna elements at the base- station antenna array in a dense scattering environment, or in a LOS propagation condition. In this paper, by using the Mellin transform of the eigenvalue distribution, we derive the semi- correlated sum-rate capacity of multi-antenna channels with an arbitrary number of antennas in closed form. Afterwards, we employ two commonly- used correlation models to compare the theoretical closed-form results and the simulated results and the final results show that they match well.

Massive multiple-input multiple-output (MIMO) is a potential candidate key technology for the fifth generation of wireless communication systems. In previous research, different power loss and shadowing effects on different individual antenna elements have been neglected. When characterizing the channel of a massive MIMO system and investigating the system performance, the large scale attenuation (LSA) over the antenna array has not been previously considered. In this paper, based on our proposed accurate geometrical propagation model, the spectral efficiency (in terms of bits/s/Hz sum-rate) result of maximal ratio combining (MRC) detection is investigated. From the simulation results, we find that the sum-rate performance for the MRC detection of our proposed more realistic channel model exceeds the results using the conventional model (where the LSA effect is not included). This proposed model LSA model is beneficial and informative for the research, design, and evaluation of the next generation of wireless communication systems employing massive MIMO configurations.

Millimeter-wave (mm-wave) systems suffer from an assortment of propagation and hardware challenges such as extremely high pathloss/shadowing and amplifier non-linearity/phase noise, respectively. In this paper, we demonstrate via simulations that non-coherent frequency shift keying (FSK) can utilize the vast bandwidth at mm-wave frequencies to combat significant pathloss and shadowing in this band, while being robust to amplifier non-linearity and phase noise. To support our findings, we establish a comprehensive simulation setup and set of parameters that consider the impact of pathloss, shadowing, amplifier non-linearity, and phase noise, at mm-wave frequencies. Our results indicate that non-coherent FSK outperforms other modulation schemes such as phase shift keying and quadrature amplitude modulation. This outcome combined with the low detection complexity of non-coherent FSK make it an attractive modulation for achieving multi Gbps wireless links at mm-wave frequencies. The proposed comprehensive simulation setup can also be applied to investigate and validate the performance of various mm-wave systems in practical settings.

Unlike solid obstacles, the excess loss of semiclosed obstacles (SCOs) can be considerably overestimated by directly applying existing diffraction models, i.e., multiedge diffraction models. By regarding the propagation situation as a superposition of the cases of the “Open Field” and the “Closed Obstacle,” this paper presents a simple way to model the excess loss of SCOs that widely exists in intelligent transportation systems. By estimating two weight coefficients according to the specific situation, this model structure can be applied to different SCOs. To illustrate our modeling concepts, two typical cut-and-cover tunnels in high-speed railway are studied in detail. Combining this case with our previous implementations for train stations and crossing bridges, a complete set of coefficients for the excess loss of the main SCOs in railway settings is presented. This case study shows that the proposed approach provides an effective and fairly simple way to include various SCOs in the network planning, simulation, and design of communication systems. As our approach has determined the coefficients empirically, the proposed model structure can provide the foundation for future work that aims to streamline the excess loss prediction via estimation of coefficients either analytically or via a reduced set of measurements.

The plane wave assumption has been used extensively in wireless channel modeling for simplicity. However, when the plane wave model is applied to the massive multiple input and multiple output (MIMO) channel characterization, it is no longer suitable. In this paper, by using the geometrical channel parameterizations, the phase shift difference caused by the spherical wave for a large linear antenna array is investigated, and the Far Region Boundary of a Linear Massive Antenna has been proposed as a criterion to determine whether the user terminal is within the near field of this large antenna structure. Finally, by using ray-tracing method, the proposed boundary within which the propagation caused phase difference exceeds 22.5 is verified. The spherical wave model is necessary for the more accurate channel characterization.

Massive multiple input and multiple output (MIMO) systems can increase the spectrum and energy efficiency of existing cells, and because of this, massive MIMO has been considered as a potential technique for next generation wireless communication networks. Since a thorough knowledge of the propagation channel is a prerequisite of reliable communication systems, massive MIMO channels are of great current interest. In this paper, based on realistic measurements in a stadium scenario in two frequency bands, the stationarity of three basic channel parameters is investigated by using the reverse arrangements test. The results show that channel behaviors in our higher frequency band are stationary over the linear antenna array, whereas this appears untrue at the low frequency band. This non-stationarity phenomenon in the line of sight propagation environment is mainly caused by the stronger reflection and smaller path loss at the low frequency band, which allows more and stronger multipath components, and this leads to substantial channel changes over the large size antenna array.

This paper explores the general framework and prospects for on-chip and off-chip wireless interconnects implemented for high-performance computing (HPC) systems in the context of micro power wireless design. HPC interconnects demand very high (≥ 10 Gb/s) transmission rates using ultraefficient (~ 1 pJ/bit) transceivers over extremely short (≤ 100 cm) ranges. In an attempt to design such wireless interconnects, first a model for the wireless communication channel properties is developed. The use of CMOS-based energyefficient on-off keying (OOK) transceiver architectures operating in the 60-90 GHz bands is considered as a practical solution. In order to address strict performance requirements of wireless HPC interconnects, and taking advantage of the recent developments in device scaling, compact low-power and innovative circuits based on novel double-gate MOSFETs (DG-MOSFETs) are proposed in the implementation of the architecture. The performance of a compact low-noise amplifier (LNA) design using common source (CS) inductive degeneration with 32 nm DGMOSFETs is investigated by quantitative analysis and simulation. The proposed inductor-less two-stage cascode cascade LNA is optimized for 90 GHz operation and has the advantage of gain switching over its CMOS counterpart without the use of additional switching transistors, which makes it remarkably power efficient and faster. As further examples of efficient and compact DG-MOSFET circuits for OOK transceiver design, a three-stage CS 5 dB tunable power amplifier operating up to 90 GHz, and a novel 90 GHz voltage controlled oscillator are also presented. This is followed by the proposal of an array of four monopole antennas studied using full-wave EM solver.

With the rise of chip multiprocessors, an energy-efficient communication fabric is required to satisfy the data rate requirements of future multi-core systems. The Network-on-Chip (NoC) paradigm is fast becoming the standard communication infrastructure to provide scalable inter-core communication. However, research has shown that metallic interconnects cause high latency and consume excess energy in NoC architectures. Emerging technologies such as on-chip wireless interconnects can alleviate the power and bandwidth problems of traditional metallic NoCs. In this paper, we propose A-WiNoC, a scalable, adaptable wireless Network-on-Chip architecture that uses energy efficient wireless transceivers and improves network throughput by dynamically re-assigning channels in response to bandwidth demands from different cores. To implement such adaptability in our network at run-time, we propose an adaptable algorithm that works in the background along with a token sharing scheme to fully utilize the wireless bandwidth efficiently. Since no wireless NoC design has been completely realized with current technology, we describe technology trends in designing energy-efficient wireless transceivers with emerging technologies. We compare our proposed A-WiNoC to both wireless and wired topologies at 64 cores, with results showing a 1.4-2.6× speedup on real applications and a 54 percent improvement in throughput for synthetic traffic. Using Synopsys Design Compiler, our results indicate that A-WiNoC saves 25-35 percent energy over other state-of-the-art networks. We show that A-WiNoC can scale to 256 cores with an energy improvement of 21 percent and a saturation throughput increase of approximately 37 percent.

The overpass is a special over-road structure for vehicle transportation, constituting one type of roadway intersection. Real-time communications between on- and under-overpass vehicles can contribute to optimal route selection and overpass accident warning messaging. In this paper, we provide measurement and analytical results for V2V propagation path loss in the 5 GHz band for two example overpasses. These example overpasses are termed the (i) one-lane metal-bottom overpass, and (ii) two-lane metal-bottom overpass. Due to the unique structure of the overpass, we divide the radio wave propagation spaces around the overpass into four different areas: a two-ray area, a short- term partial shadowing area, a (full) shadowing area, and a long-term partial shadowing area. Analysis and measured results for propagation path loss in these areas are provided. In the two-ray area, a line-of-sight (LoS) path and a ground reflected path are present, whereas in the other areas, the overpass body (floor, walls and columns) block the propagation of energy, increasing path loss. We briefly describe our geometry-based models for the overpass V2V channel, which make use of our analytical models and the measurement data.

We provide measurement results from an air-to-ground channel measurement campaign undertaken in a hilly terrain suburban environment. This campaign is part of a larger project-sponsored by NASA-aimed at developing measurement based models for the air-to-ground channel, for use in evaluation of unmanned aircraft system (UAS) communication link development. Our measurements provide dual-band SIMO power delay profiles, from which we compute propagation path loss, root-mean square delay spread, and correlations among the two bands. The two signal frequencies are 968 MHz and 5060 MHz. For this hilly environment, average propagation path loss follows the curved-earth two-ray model, with reduced variation about this model attributable to multiple weaker reflections and scattering from the hilly terrain and buildings. Root-mean square delay spreads vary, with the majority of values 10-20 ns, but occasional larger values of nearly 1000 ns. As expected, the line of sight signal components in the two bands are essentially uncorrelated, but correlations for the signal components on the two antennas in the same band vary depending upon flight path geometry.

High-speed railway (HSR) brings convenience to peoples' lives and is generally considered as one of the most sustainable developments for ground transportation. One of the important parts of HSR construction is the signaling system, which is also called the “operation control system,” where wireless communications play a key role in the transmission of train control data. We discuss in detail the main differences in scientific research for wireless communications between the HSR operation scenarios and the conventional public land mobile scenarios. The latest research progress in wireless channel modeling in viaducts, cuttings, and tunnels scenarios are discussed. The characteristics of nonstationary channel and the line-of-sight (LOS) sparse and LOS multiple-input-multiple-output channels, which are the typical channels in HSR scenarios, are analyzed. Some novel concepts such as composite transportation and key challenging techniques such as train-to-train communication, vacuum maglev train techniques, the security for HSR, and the fifth-generation wireless communications related techniques for future HSR development for safer, more comfortable, and more secure HSR operation are also discussed.

We report on peer-to-peer large-scale wireless channel characteristics for an urban environment in six public-safety bands, for five simultaneous receiving sites. Results are based upon measurements taken in Denver in July 2009 with stationary receivers and a pedestrian transmitter. The six frequencies at which we measured are (in MHz) 430, 750, 905, 1834, 2400, and 4860. We quantify both site and frequency diversity, and show that 5-site selection yields minimum average gains of 15 dB in mean received power levels; 5-site selection diversity also reduces received power variation by 17-29 dB, depending on frequency. Frequency diversity yields similar gains. By approximating received powers as lognormal, we describe an analytical method to approximate the cdf of the per-site, or per-frequency (or both) maximum received power. These data and diversity models should be useful for public-safety and ad hoc communication system designers, and for cooperative diversity schemes, wherein multiple users act as a virtual array.

We provide some measured channel characterization results for two elevator shaft channels in the 5-GHz band, for two distinct elevator shaft types in two buildings. The elevator shaft channel is of interest for several applications, including public safety. Even though other authors have reported elevator shaft channel characteristics for lower-frequency bands (255-MHz, 900-MHz, 1.9-GHz), to our knowledge ours is the first work for the 5-GHz band. Prior work has also not thoroughly addressed channel characteristics when the elevator car is in motion, whereas here we provide some initial measurement results for this dynamic condition. We measured power delay profiles and from these estimated propagation path loss and root-mean square delay spread (RMS-DS). Path loss exponents were approximately 2 in one building and 6 in the other. Mean RMS-DS values range from 14–60 ns when the elevator car is motionless, with RMS-DS generally increasing with link distance. Maximum RMS-DS values increase to 58 ns and 70 ns in the two buildings when the elevator car is moving and the receiver is inside the car.

With the increasing number of cores in chip multiprocessors, the design of an efficient communication fabric is essential to satisfy the bandwidth and energy requirements of multi-core systems. Scalable Network-on-Chip (NoC) designs are quickly becoming the standard communication framework to replace bus-based networks. However, the conventional metallic interconnects for inter-core communication consume excess energy and lower throughput which are major bottlenecks in NoC architectures. On-chip wireless interconnects can alleviate the power and bandwidth problems of traditional metallic NoCs. In this paper, we propose an adaptable wireless Network-on-Chip architecture (A-WiNoC) that uses adaptable and energy efficient wireless transceivers to improve network power and throughput by adapting channels according to traffic patterns. Our adaptable algorithm uses link utilization statistics to re-allocate wireless channels and a token sharing scheme to fully utilize the wireless bandwidth efficiently. We compare our proposed A-WiNoC to both wireless/electrical topologies with results showing a throughput improvement of 65%, a speedup between 1.4-2.6X on real benchmarks, and an energy savings of 25-35%.

We provide results for propagation path loss and root-mean-square delay spread within a parking garage, in the 5 GHz band, aimed at V2V applications. Results for both same-floor, and floor-to-floor propagation are shown for a typical urban parking garage structure. For line-of-sight (LOS) conditions, same-floor propagation path loss is well approximated by a 2-ray model. Same-floor non-LOS path loss shows path loss exponent n-3. Path loss for the floor-to-floor case can be well-modeled by accounting for floor attenuation factors and an additional loss that represents distance of the mobile toward the garage interior, away from the garage's open sides, i.e., a model that accounts for both vertical and horizontal distance. Mean delay spreads reach nearly 150 ns for the same-floor case, and reduce to ~50 ns for the longest (3-floor) distance floor-to-floor case. Since there have been few results for such environments previously published, our results should prove useful for V2V systems deployed in parking garages.

In this paper we provide channel characterization results for the elevator shaft channel in the 5-GHz band, based upon measurements conducted in four buildings. This channel is of interest for several applications, including WiFi and public safety. Although several authors have provided elevator shaft channel characteristics for lower-frequency bands (255-MHz, 900-MHz, 1.9-GHz), to our knowledge this is the first work that addresses the 5-GHz band. Moreover, prior work has not thoroughly addressed channel characteristics when the elevator car is in motion, whereas here we provide measurement and modeling results for this dynamic condition. Our measurements were of power delay profiles, from which we estimated propagation path loss and root-mean square delay spread (RMS-DS). Path loss exponents were approximately 2.5 in one building and 5.5 in the other three buildings, with standard deviations about the log-distance linear fits equal to approximately 3 dB and 5.5 dB, respectively. Mean RMS-DS values range from approximately 14-60 ns when the elevator car is motionless. Maximum RMS-DS values were 144 ns and 152 ns in the two different types of buildings when the elevator car is moving. The significant differences in these channel characteristics among the four buildings are likely attributable to the distinct physical features of the buildings.

The area of wireless ad hoc networks has attracted much attention and gained great popularity in the last few years. Yet researchers are still investigating several metrics to evaluate ad hoc network performance. Furthermore, to our knowledge, no work has been published to address the comparison of different network metrics. In this paper, we analyze and compare several distinct network metrics including transport capacity, transmission capacity and network diameter, which quantify ad hoc network performance from different perspectives. We also evaluate the network metrics via simulation for two “extreme” routing strategies: “nearest neighbor” (NN) and “shortest path” (SP). Main conclusions are that the transport capacity and the transmission capacity are generally inversely related in ad hoc networks; SP routing can achieve larger transport capacity and smaller network diameter than NN routing, whereas NN routing results in larger transmission capacity than SP routing. Ultimately, the best network metric among these three depends upon application; more research is needed in this important area.

We report on models developed for peer-to-peer (ground-based) wireless channels for an urban environment in the 700 MHz and 4.9 GHz bands, both allocated for public safety and “emergency responder” applications. Results are based upon measurements taken in downtown Denver, CO for link distances up to approximately 100 m. Heretofore, measurement-based models for an urban environment in these bands and for low antenna heights have not been developed. Our measurements employed a vector network analyzer, from which log-distance models for path loss and dispersive channel models have been extracted. Our dispersive channel models employ a statistical algorithm for the number of multipath components, previously used only in indoor settings. The channel models should be useful for public safety communication system designers.

This paper presents wideband wireless channel characterization results for intra-automobile communication in the 5 GHz band. Results pertain to data collected from a mini-van and bus, both parked. Motivating this work is the scarcity of results for intra-automobile wireless channel characteristics. This paper describes some related work, the measurement conditions and procedures, and resulting channel characteristics for the two environments. Measurements were taken using a 50 MHz bandwidth spread spectrum correlator channel sounder, and power delay profiles (PDPs) were collected. We provide root-mean square delay spread (RMS-DS) statistics, and statistical channel models for these two intra-automobile channels. Mean RMS-DS values are approximately 17 ns in the mini-van, and 17 and 22 ns for measurements with two different transmitter locations in the bus. RMS-DS standard deviations range from 2-6 ns. As expected, the RMS-DS values increase with vehicle size and transmitter-receiver distance. Both human movement and the unique physical structures of the intra-automobile environment also strongly affect the channel's characteristics.

Vehicle-to-vehicle (V2V) communications have seen growing attention in the last few years. In this work, we address the use of the 3GPP Long Term Evolution (LTE) standard technology applied to V2V. We employ empirical models for the V2V channel, and show results from comprehensive computer simulations, based upon both the uplink (UL) and downlink (DL) standards for LTE. We provide results for 10 MHz and 20 MHz channels, in terms of BER, BLER, spectral efficiency and throughput, using multiple MIMO modes. Results show the attractive feasibility of the LTE technology in V2V communication systems.

Analytical expressions for the probability density function of block-wise signal-to-noise-plus-interference ratio for both synchronous and asynchronous direct-sequence spread spectrum code-division multiple access systems are developed, for equal average energy signals on the Gaussian and Rayleigh flat fading channels. Using the standard Gaussian approximation for multi-user interference, accurate density approximations are obtained, which agree very well with computer simulation results.

A simple and efficient method for generating correlated multivariate Weibull random variables with arbitrary fading parameters and arbitrary average powers is proposed. The multivariate Weibull random variables generated via this method can be used to simulate the performance of wireless communication systems with any diversity order or channel impulse response length, under arbitrary correlated Weibull fading conditions.

In this paper, we describe the results of a channel measurement and modeling campaign for the vehicle-to-vehicle (V2V) channel in the 5-GHz band. We describe measurements and results for delay spread, amplitude statistics, and correlations for multiple V2V environments. We also discuss considerations used in developing statistical channel models for these environments and provide some sample results. Several statistical channel models are presented, and using simulation results, we elucidate tradeoffs between model implementation complexity and fidelity. The channel models presented should be useful for system designers in future V2V communication systems.

In this paper, we examine performance of a multi-stage parallel interference cancellation (PIC) receiver using a generalized soft limiter. The generalized soft limiter (GSL) improves the accuracy of the reconstructed interference signals by making hard decisions on "reliable" signals and partial soft decisions on "unreliable" signals. The system performance degradation caused by imperfect amplitude estimation and near-far effects is also analyzed in the paper. It is also shown that GSL-PIC can achieve comparable performance to that of hyperbolic tangent decision PIC (HT-PIC), which has been shown to be the optimum decision for the single user case with Gaussian interference and noise. The advantage of the GSL is that it is much easier to implement than the HT. Both GSL-PIC and HT-PIC are shown to be able to achieve performance much better than other improved PIC techniques such as null-zone decision PIC (NZ-PIQ, soft-limiter PIC, and partial PIC (PPIC) in most scenarios.

Vehicle to vehicle (V2V) communications have drawn much attention in recent years. In this paper, we discuss tradeoffs between implementation complexity and accuracy of several stochastic channel models for the V2V environment, and then address spread spectrum system performance attained using these channel models. Two different propagation environments are considered: urban and open areas (highways). The necessity of employing non-stationary channel models to accurately represent the channel is substantiated by comparing stationary and non-stationary empirical model outputs with measured data. A framework to compare single carrier direct sequence code division multiple access (SC-DS-CDMA) and multicarrier DS-CDMA (MC-DS-CDMA) performance in V2V channels is presented, and bit error ratio (BER) performance of the schemes is provided for the two channels. Our comparison of single- and multi-user performance shows that MC-DS-CDMA performs better than SC-DS-CDMA in both V2V environments.

Statistical parallel interference cancellation (STPIC) is a reduced complexity IC technique in which IC is performed only on a small percentage of "unreliable" bits. In this paper, we extend our previous STPIC analysis for single rate direct sequence-code division multiple access (DS-CDMA) systems over flat fading channels to multi-rate systems with variable spreading gain (VSG) over dispersive fading channels. We show that with STPIC, both low rate (LR) and high rate (HR) users can achieve performance similar to or better than full PIC, but with reduced computational complexity. We also show that for LR users STPIC BER analysis based on the Gaussian approximation (GA) matches simulated results well at low signal-to-noise ratios (SNRs) and is slightly optimistic at high SNRs; whereas for HR users with small processing gains, the GA analysis can be either optimistic or pessimistic depending on SNRs, the IC threshold u, and loading factors.

Vehicle to vehicle (V2V) communications have drawn much attention in the past few years. The IEEE 802.16e standard systems can be considered potential candidates for these applications due to their attractive features, like high data rate, mobility support, etc. In this paper, we evaluate the performance of an 802.16e system with the OFDMA air interface in two non-stationary vehicle to vehicle (V2V) channels: an open area high traffic density (OHT) channel and an urban (UOC) channel. We first introduce the non-stationary V2V channel models developed from empirical data. Then we provide a brief overview of 802.16e and introduce three channel estimation schemes that apply to different scenarios. Finally, we evaluate the performance of the 802.16e system over the proposed non-stationary V2V channel models. We show that the proposed channel estimation methods provide a good tradeoff between channel estimation accuracy and computational complexity. We also illustrate that system performance in non-stationary channels is more volatile than in stationary channels.

We present a reduced-complexity parallel interference cancellation (PIC) technique, in which PIC is performed only on "unreliable" bits (blocks). We term our technique statistical PIC (STPIC), since the decision to employ PIC for any user signal is based upon received signal statistics. Here we propose two different methods: one is bitwise (instantaneous) STPIC (ISTPIC), in which IC is performed only on the bits whose absolute log likelihood ratio (LLR) is below a pre-selected threshold; the other method is block STPIC (BSTPIC), in which IC is performed only on the blocks whose average signal-to-noise-plus-interference ratio (SNIR) is below a pre-selected threshold. Both LLR and SNIR statistics reduce to quantities simple to obtain. We show that STPIC can achieve performance equivalent to conventional full PIC (FPIC) and other partial PIC techniques in flat Rayleigh fading channels, but with reduced computational complexity. We also show our proposed ISTPIC can achieve performance better than FPIC in good channel conditions (e.g., AWGN), still with reduced computational complexity. The ISTPIC performance gain over conventional FPIC is larger in conditions of larger loading factor where efficient IC techniques are more likely to be needed

In this paper we describe results of a channel measurement campaign for modeling the V2V channel. After review of applications, potential frequency bands, and related work, we describe the measurements and results for delay spreads and multipath component fading amplitudes and correlations, made in multiple V2V environments. We also note how the V2V channel can differ appreciably from other common terrestrial (e.g., cellular) channels. We describe considerations used in developing the statistical channel models for these environments, and provide some example measurement and modeling results that should be useful for system designers in future V2V applications

In this paper, we describe a generalized scheme to analyze the bit error probability of Hamming codes when the code symbols have different symbol energies. The method of analysis is general, and could be used to analyze other block code schemes. We illustrate the effectiveness of our method with application to a spectrally-shaped multicarrier direct-sequence spread spectrum system.

Abstract—This paper describes a test-bed for technology that unifies agent based computing and adaptive resource management for dynamic real-time systems. We describe a unified framework that combines a hybrid agent based architecture with explicit resource adapting mechanisms. I.

Considers trellis decoding of convolutional codes with selectable effort, as measured by decoder complexity. Decoding is described for single parent codes with a variety of complexities, with performance "near" that of the optimal fixed receiver complexity coding system. Effective free distance is examined. Criteria are proposed for ranking parent codes, and some codes found to be best according to the criteria are tabulated, Several codes with effective free distance better than the best code of comparable complexity were found. Asymptotic (high SNR) performance analysis and error propagation are discussed. Simulation results are also provided.

Detection for the statistically known channel (SKC) is aimed at obtaining good performance in situations where our statistical knowledge of a time-varying channel is good, and where other equalization/detection schemes are either too complex to implement, or their performance is limited due to the rapidity of channel fading, or where we are simply unable to perform channel estimation. By using a statistical characterization of the channel, we develop a new detector that performs maximum-likelihood sequence estimation (MLSE) (given the channel model) on blocks of N symbols. Both symbol-spaced and fractionally spaced samples are used, to obtain two different detectors, that are generalizations of those devised for optimal block schemes on nondispersive channels. The detector that uses fractionally spaced samples is shown to outperform the detector that uses symbol-spaced samples. The performance of both appears to approach that of the corresponding known channel (KC) detector as the block length increases. We also numerically evaluate the SKC detector performance under conditions where the channel parameters (statistics) are incorrectly estimated, and show that the fractionally spaced detector is fairly robust to modeling errors. Finally, we devise a sliding block algorithm, for use when transmitting more than N symbols.