Spatial Channel Models (SCM) used in wireless system simulations are determined by Large-Scale Parameters (LSP). LSPs include delay spread, shadow fading, angle of arrival and departure spread, and Rice K for line-of-sight channels. LSPs are modeled as a spatially correlated random field over the geometry of the network scenario being simulated. The general method is to generate an LSP map on a discrete lattice (or grid) and induce spatial correlation via spatial filtering as determined by the LSP's correlation distance. This step represents a large part of the simulator's computation load, which leads to the use of a coarsely spaced lattice and interpolation from nearest lattice points to arbitrary UE locations on the x-y plane. We investigate the computation vs. fidelity trade associated with LSP generation. We will show that when a coarse grid is employed, there can be significant nonstationary distortion of the LSP correlation due to the interpolation step. We investigate three different interpolators having varying correlation fidelity and computation load.

Dedicated Short-Range Communications (DSRC) has been designed to support vehicular communications. In the U.S., DSRC operates in the 5.9 GHz licensed spectrum band. Its physical (PHY) and medium access control (MAC) layers, defined in the IEEE 802.11p standard, are based on the IEEE 802.11 family of Wi-Fi standards. Vehicular communication environments differ significantly from the sparse and low-velocity nomadic use cases of a typical Wi-Fi deployment. Thus, there are many challenges to adapt Wi-Fi technologies to support the unique requirements of vehicular communications such as achieving high and reliable performance in highly mobile, often densely populated, and frequently non-line-of-sight environments. The automotive and the communications industries, academia, and governments around the world have been devoting tremendous efforts to address these challenges, and significant achievements have been made. Remaining challenges can be addressed by the future versions of DSRC. In this paper, we investigate the current technologies used by DSRC to support vehicle safety communications, analyze existing and possible DSRC performance enhancements that can be realized in the near term, and provide a few initial thoughts on the DSRC evolution path.

This paper formulates a general framework that includes and extends the existing definitions for network survivability. Based on this framework, network survivability is characterized by a survivability function rather than a single-value survivability measure, and various quantities of interest can be derived from the function. Examples are the expected survivability, the worst-case survivability, the r-percentile survivability, and the probability of zero survivability. The survivability function is especially useful for the study of large-scale disasters. For illustration, the authors derive the survivability function in closed form for a simple ring network under link failures. They also discuss the general procedure for finding survivability functions for complex networks, and show that the survivability function reveals useful information about a network. This framework provides a unified and practical approach to analyzing and designing highly survivable communications networks.>

The performance of a class of asymmetric packet switch modules with channel grouping is analyzed. The switch module considered has n inputs and m outputs. A packet destined for a particular output address (out of g) needs to access only one of the r available physical output ports: m=gr. These switch modules are the key building blocks in many large multistage switch architectures. The focus is on the performance of input-buffered and output-buffered switch modules under geometrically bursty traffic. A combination of exact derivation, numerical analysis, and simulation yields the saturation throughput of input-buffered switch modules and the mean delay of the input-buffered and output-buffered switch modules. Tables and formulas useful for traffic engineering are presented. The results show that increasing the number of output ports per output address (r) can significantly improve switch performance, especially when traffic is bursty. Although output-buffered switch modules have significantly better performance than input-buffered switch modules when there are equal numbers of input and output ports, this performance difference becomes significantly smaller when the switch dimensions are asymmetric.>

The switch modules are studied because they are the key building blocks in large multistage switch architectures. The switch module considered has n inputs and m outputs. A packet destined for a particular output address (out of g) needs to access only one of the r available physical output ports: m=gr. Input-buffered, output-buffered, and unbuffered switch modules are studied. The results show that increasing the number of output ports per output address (r) can significantly improve the performance of buffered as well as unbuffered switch modules. For acceptable performance, the difference in throughput between buffered and unbuffered switch modules is considerable. For buffered switch modules, an interesting observation is that although output-buffered switch modules have significantly better delay performance than input-buffered switch modules when n=gr, the performance difference is diminished as one deviates from these switch dimensions.>

Analyses of four broadband fiber-optic subscriber loop architectures, including active (high-speed time division multiplexing (TDM)-based) and passive (dense wavelength division multiplexing (WDM)-based, WDM-based with an analog subcarrier-multiplexing overlay, and splitter-based) double-star topologies, are presented. The analyses focus on specific demonstrated architectures and use component cost projections based on learning curves to estimate future network costs on a per-subscriber basis. Also investigated is the sensitivity of projected cost-per-subscriber to remote multiplexing node size and to double-star prove-in distance. The results indicate that the four architectures have very different double-star prove-in distances and that loop costs are minimized for much smaller remote node sizes than active loops, thus permitting cost-effective deployment of passive loops for smaller groups of subscribers. In addition, cost breakdowns for the four architectures indicate that splitter-based passive loops share electronics more effectively among subscribers than loop architectures requiring dedicated (per-subscriber) electronic interfaces, resulting in projected cost advantages for the splitter-based networks.>