David W. Matolak

iWISE: Inter-router Wireless Scalable Express Channels for Network-on-Chips (NoCs) Architecture

Network-on-Chips (NoCs) paradigm is fast becoming a defacto standard for designing communication infrastructure for multicores with the dual goals of reducing power consumption while improving performance. However, research has shown that power consumption and wiring complexity will be two of the major constraints that will hinder the growth of future NoCs architecture. This has resulted in the investigation of emerging technologies and devices to alleviate the power and performance bottleneck in NoCs. In this paper, we propose iWISE, an inter-router wireless scalable express channels for NoCs architecture that minimizes the power consumption via hybrid wireless communication channels, reduces the area overhead with smaller routers and shared buffers, and improves performance by minimizing the hop count. We compared our network to leading electrical and wireless topologies such as mesh, concentrated mesh, flattened butterfly and other wireless hybrid topologies. Our simulation results on real applications such as Splash-2, PARSEC, and SPEC2006 for 64 core architectures indicate that we save 2X power and 2X area while improving performance significantly. We show that iWISE can be further scaled to 256 cores while achieving a 2.5X performance increase and saving of 2X power when compared to other wireless networks on synthetic workloads.

Air-ground channels & models: Comprehensive review and considerations for unmanned aircraft systems

Use of unmanned aircraft systems (UASs) for multiple applications is expected to grow dramatically in the coming decades; this fact has motivated this papers focus on fundamental physical layer characteristics relevant to UAS communications. In the past, for aeronautical communications with high transmitted power levels, narrow signal bandwidths, elevated ground site antennas in open areas, and low duty cycle transmissions, simple models for channel attenuation sufficed. In the future, when UAS ground stations may not all be in cleared areas with elevated antennas, higher data rates (wider bandwidths) are required, and small UASs with stringent power limitations still require high reliability, more comprehensive air-ground (AG) channel characteristics will be required in order to ensure robust signal designs for high-reliability AG links. We have found that no accurate, validated wideband models exist for the AG channel, particularly not in the Land C-bands that are being proposed for UASs. Airframe shadowing models also do not yet exist. We thus provide a comprehensive review of past work on the AG channel, and follow this with a brief description of plans for an AG channel measurement and modeling campaign. Resulting AG channel models will subsequently be used in the evaluation of candidate air interfaces for UAS control and non-payload communications (CNPC). The air interface must operate in the presence of both delay and Doppler spreads, and shadowing. It should also be spectrally efficient, low-latency, and reasonably robust to interference. We discuss these AG air interface considerations, and also show some initial modeling results based on both analysis and measurements.

5 GHZ wireless channel characterization for vehicle to vehicle communications

We provide channel modeling results based upon measurements of the vehicle-to-vehicle (VTV) mobile channel, taken in the 5 GHz frequency band. Our measurements pertain to three types of areas: large cities, open highway areas, and small cities. A spread-spectrum stepped correlator technique was used, with omnidirectional antennas either atop or inside the vehicles. We provide measured and analytical results in the form of power delay profiles and frequency correlation function estimates. Delay spread statistics for these environments, as well as approximate amplitude fading distributions are also provided. The largest values of root-mean-square delay spreads, on the order of 1 microsecond, were obtained in urban areas with dense vehicle traffic, corresponding to coherence bandwidths of as low as 1-2 MHz. Fading amplitude statistics are best fit with a Nakagami-m distribution. Fading channel statistics for an example 10 MHz channel bandwidth are also provided.

Worse-than-Rayleigh fading: Experimental results and theoretical models

This article is motivated by the recent recognition that channel fading for new wireless applications is not always well described by traditional models used for mobile communication systems. In particular, fading data collected for vehicleto- vehicle and wireless sensor network applications has motivated new models for conditions in which channel fading statistics can be worse than Rayleigh. We review the use of statistical channel models, describe our example applications, and provide both measured and modeling results for these severe fading conditions.

The 5-GHz Airport Surface Area Channel—Part II: Measurement and Modeling Results for Small Airports

This paper describes results from a channel measurement campaign performed at several small airports in the U.S. in the 5-GHz band. This paper is a companion to another paper, which describes channel models for large airports. We classify the small airport surface channel into three propagation regions based upon different delay dispersion conditions. The channel characteristics of these regions in the delay and frequency domains are discussed with examples. We provide empirical stochastic channel models (of different bandwidths) to accurately represent the channel on the airport surface area for all propagation regions. The models are provided in the form of tapped delay lines, and complete statistical tap descriptions are given. Several key observations, including the presence of severe amplitude fading, some correlated scattering, and statistically nonstationary behavior, are also discussed.

Wireless networks-on-chips: architecture, wireless channel, and devices

Wireless networks-on-chips (WINoCs) hold substantial promise for enhancing multicore integrated circuit performance, by augmenting conventional wired interconnects. As the number of cores per IC grows, intercore communication requirements will also grow, and WINoCs can be used to both save power and reduce latency. In this article, we briefly describe some of the key challenges with WINoC implementation, and also describe our example design, iWISE, which is a scalable wireless interconnect design. We show that the integration of wireless interconnects with wired interconnects in NoCs can reduce overall network power by 34 percent while achieving a speedup of 2.54 on real applications.

Wireless Channels that Exhibit "Worse than Rayleigh" Fading: Analytical and Measurement Results

We describe several disparate practical settings in which cases of severe, or worse than Rayleigh, fading have been encountered. To explain this behavior, we present two physical models. The first model employs a statistically non-stationary random process that switches between two distributions, akin to the multi-state models proposed for land mobile satellite channels. The other model we propose is a multiplicative model of two small scale fading processes. We also describe the analytical pdf for such a multiplicative model using two Weibull random variables as the underlying small scale fading distributions. Measured data is used to corroborate these models, and our computer simulations confirm the ability to replicate the statistics of these severe fading processes. These proposed models can be used by researchers investigating communication system designs in severe fading environments

Channel Modeling for V2V Communications

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

3-D outside cell interference factor for an air-ground CDMA "cellular" system

We compute the outside-cell interference factor of a code-division multiple-access (CDMA) system for a three-dimensional (3-D) air-to-ground (AG) cellular-like network consisting of a set of uniformly distributed ground base stations and airborne mobile users. The CDMA capacity is roughly inversely proportional to the outside-cell interference factor. It is shown that for the nearly free-space propagation environment of these systems, the outside-cell interference factor can be larger than that for terrestrial propagation models (as expected) and depends approximately logarithmically upon both the cell height and cell radius.

Performance Evaluation of 802.16e in Vehicle to Vehicle Channels

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.